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  <title>R2RML: RDB to RDF Mapping Language</title>
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    <p><a href="http://www.w3.org/"><img src="http://www.w3.org/Icons/w3c_home" alt="W3C"
    height="48" width="72" /></a></p>

    <h1><a name="title" id="title"></a>R2RML: RDB to RDF Mapping Language</h1>

    <h2><a name="w3c-doctype" id="w3c-doctype"></a><em>W3C Working Draft 20 September 2011</em></h2>

    <dl>
 	   <dt>This version:</dt> 

	   <dd><a href="http://www.w3.org/TR/2011/WD-r2rml-20110920/">http://www.w3.org/TR/2011/WD-r2rml-20110920/</a></dd> 

      <dt>Latest Editor's Draft:</dt>

      <dd><a href=
      "http://www.w3.org/2001/sw/rdb2rdf/r2rml/">http://www.w3.org/2001/sw/rdb2rdf/r2rml/</a></dd>

      <dt>Latest published version:</dt>

      <dd><a href="http://www.w3.org/TR/r2rml/">http://www.w3.org/TR/r2rml/</a></dd>

      <dt>Previous version:</dt>

      <dd><a href=
      "http://www.w3.org/TR/2011/WD-r2rml-20110324/">http://www.w3.org/TR/2011/WD-r2rml-20110324/</a></dd>

      <dt>Editors:</dt>

      <dd>Souripriya Das, Oracle</dd>

      <dd>Seema Sundara, Oracle</dd>

      <dd>Richard Cyganiak, DERI, National University of Ireland, Galway</dd>
    </dl>

    <p class="copyright"><a href=
    "http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> &copy;
    2011 <a href="http://www.w3.org/"><acronym title=
    "World Wide Web Consortium">W3C</acronym></a><sup>&reg;</sup> (<a href=
    "http://www.csail.mit.edu/"><acronym title=
    "Massachusetts Institute of Technology">MIT</acronym></a>, <a href=
    "http://www.ercim.eu/"><acronym title=
    "European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>,
    <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a href=
    "http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
    <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
    and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a>
    rules apply.</p>
  </div>
  <hr />

  <h2><a name="abstract" id="abstract"></a>Abstract</h2>

  <p>This document describes R2RML, a language for expressing customized mappings from
  relational databases to RDF datasets. Such mappings provide the ability to view
  existing relational data in the RDF data model, expressed in a structure and target
  vocabulary of the mapping author's choice. R2RML mappings are themselves RDF graphs and
  written down in Turtle syntax. R2RML enables different types of mapping
  implementations. Processors could, for example, offer a virtual SPARQL endpoint over
  the mapped relational data, or generate RDF dumps, or offer a Linked Data
  interface.</p>

  <div>
    <h2><a name="status" id="status"></a>Status of this Document</h2>

    <p><em>This section describes the status of this document at the time of its
    publication. Other documents may supersede this document. A list of current W3C
    publications and the latest revision of this technical report can be found in the
    <a href="http://www.w3.org/TR/">W3C technical reports index</a> at
    http://www.w3.org/TR/.</em></p>

	<p>This document is a <a href="http://www.w3.org/2005/10/Process-20051014/tr.html#last-call">Last Call Working Draft</a> of the "R2RML: RDB to RDF Mapping Language". Publication as a Last Call Working Draft indicates that the <a href="http://www.w3.org/2001/sw/rdb2rdf/">RDB2RDF Working Group</a> believes it has addressed all substantive issues and that the document is stable. The Working Group expects to advance this specification to <a href="http://www.w3.org/2004/02/Process-20040205/tr.html#RecsW3C">Recommendation Status</a>.</p><p>Comments on this document should be sent to <a href="mailto:public-rdb2rdf-comments@w3.org">public-rdb2rdf-comments@w3.org</a>, a mailing list with 
	      a <a href="http://lists.w3.org/Archives/Public/public-rdb2rdf-comments/">public archive</a>. Comments on this working draft are due on or before <strong>1 November 2011</strong>. </p>

    <p>Publication as a Working Draft does not imply endorsement by the W3C Membership.
    This is a draft document and may be updated, replaced or obsoleted by other documents
    at any time. It is inappropriate to cite this document as other than work in
    progress.</p>

    <p>This document was produced by the
    <a href="http://www.w3.org/2001/sw/rdb2rdf/">W3C RDB2RDF Working Group</a>.
    R2RML has changed significantly since the previous Working Draft. Much of the
    document has been rewritten, many terms were renamed and other design details
    have changed. New language features include
    a detailed
    account of the <a href="#datatype-conversions">conversion of SQL datatypes
    to RDF</a>. The <a href="#generated-rdf">triples in the output dataset</a>
    are now more accurately specified. One major open question remains, and the
    working group seeks feedback on it: should
    R2RML processors be <a href="#syntax">required to support the Turtle
    syntax</a>? Apart from this, the working group anticipates no major further
    changes.</p>

    <p>This document was produced by a group operating under the <a href=
    "http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
    Policy</a>. W3C maintains a <a rel="disclosure" href=
    "http://www.w3.org/2004/01/pp-impl/43889/status">public list of any patent
    disclosures</a> made in connection with the deliverables of the group; that page also
    includes instructions for disclosing a patent. An individual who has actual knowledge
    of a patent which the individual believes contains <a href=
    "http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
    Claim(s)</a> must disclose the information in accordance with <a href=
    "http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of
    the W3C Patent Policy</a>.</p>
  </div>

  <div class="toc">
    <h2><a name="contents" id="contents"></a>Table of Contents</h2>

<ul class="toc">
  <li><a href="#introduction">1 Introduction</a>
  <ul>
    <li><a href="#conventions">1.1 Document Conventions</a></li>
  </ul></li>
  <li><a href="#overview">2 R2RML Overview and Example (Informative)</a>
  <ul>
    <li><a href="#example-input-database">2.1 Example Input Database</a></li>
    <li><a href="#desired-rdf">2.2 Desired RDF Output</a></li>
    <li><a href="#example-simple">2.3 Example: Mapping a Simple Table</a></li>
    <li><a href="#example-r2rml-view">2.4 Example: Computing a Property with an R2RML View</a></li>
    <li><a href="#example-fk">2.5 Example: Linking Two Tables</a></li>
    <li><a href="#example-m2m">2.6 Example: Many-to-Many Tables</a></li>
  </ul></li>
  <li><a href="#conformance">3 Conformance</a></li>
  <li><a href="#definitions">4 R2RML Processors and Mapping Documents</a>
  <ul>
    <li><a href="#vocabulary">4.1 Mapping Graphs and the R2RML Vocabulary</a></li>
    <li><a href="#syntax">4.2 RDF-based Turtle Syntax; Media Type</a></li>
    <li><a href="#data-errors">4.3 Data Errors</a></li>
  </ul></li>
  <li><a href="#logical-tables">5 Defining Logical Tables</a>
  <ul>
    <li><a href="#physical-tables">5.1 Base Tables and SQL Views (<code>rr:tableName</code>)</a></li>
    <li><a href="#r2rml-views">5.2 R2RML Views (<code>rr:sqlQuery</code>)</a></li>
  </ul></li>
  <li><a href="#triples-map">6 Mapping Logical Tables to RDF with Triples Maps</a>
  <ul>
    <li><a href="#subject-map">6.1 Creating Resources with Subject Maps</a></li>
    <li><a href="#typing">6.2 Typing Resources (<code>rr:class</code>)</a></li>
    <li><a href="#predicate-object-map">6.3 Creating Properties and Values with Predicate-Object Maps</a></li>
  </ul></li>
  <li><a href="#term-map">7 Creating RDF Terms with Term Maps</a>
  <ul>
    <li><a href="#constant">7.1 Constant RDF Terms (<code>rr:constant</code>)</a></li>
    <li><a href="#from-column">7.2 From a Column (<code>rr:column</code>)</a></li>
    <li><a href="#from-template">7.3 From a Template (<code>rr:template</code>)</a></li>
    <li><a href="#termtype">7.4 IRIs, Literal, Blank Nodes (<code>rr:termType</code>)</a></li>
    <li><a href="#language-tags">7.5 Language Tags (<code>rr:language</code>)</a></li>
    <li><a href="#typed-literals">7.6 Typed Literals (<code>rr:datatype</code>)</a></li>
    <li><a href="#inverse">7.7 Inverse Expressions (<code>rr:inverseExpression</code>)</a></li>
  </ul></li>
  <li><a href="#foreign-key">8 Foreign Key Relationships among Logical Tables (<code>rr:parentTriplesMap</code>, <code>rr:joinCondition</code>, <code>rr:child</code> and <code>rr:parent</code>)</a></li>
  <li><a href="#named-graphs">9 Assigning Triples to Named Graphs</a>
  <ul>
    <li><a href="#blank-nodes">9.1 Scope of Blank Nodes</a></li>
  </ul></li>
  <li><a href="#datatype-conversions">10 Datatype Conversions</a>
  <ul>
    <li><a href="#datatype-table">10.1 Table of Corresponding Datatypes</a></li>
    <li><a href="#to-string">10.2 Conversion to String</a></li>
    <li><a href="#to-boolean">10.3 Conversion to <code>xsd:boolean</code></a></li>
    <li><a href="#datetime">10.4 Conversion to Datetime</a></li>
    <li><a href="#binary">10.5 Conversion to <code>xsd:base64Binary</code></a></li>
  </ul></li>
  <li><a href="#generated-rdf">11 The Output Dataset</a>
  <ul>
    <li><a href="#generated-triples">11.1 The Generated RDF Triples of a Triples Map</a></li>
    <li><a href="#generated-rdf-terms">11.2 The Generated RDF Terms of a Term Map</a></li>
  </ul></li>
  <li><a href="#terminology">A. RDF Terminology (Informative)</a></li>
  <li><a href="#index">B. Index of R2RML Vocabulary Terms (Informative)</a>
  <ul>
    <li><a href="#class-index">B.1 Classes</a></li>
    <li><a href="#property-index">B.2 Properties</a></li>
    <li><a href="#other-index">B.3 Other Terms</a></li>
  </ul></li>
  <li><a href="#references">C. References</a>
  <ul>
    <li><a href="#normative-refs">C.1 Normative References</a></li>
    <li><a href="#non-normative-refs">C.2 Other References</a></li>
  </ul></li>
  <li><a href="#acknowledgements">D. Acknowledgements (Informative)</a></li>
</ul>

</div>

  <hr />

  <div class="body">
    <h2><a name="introduction" id="introduction"></a>1 Introduction</h2>

    <p>This specification describes R2RML, a language for expressing customized mappings
    from relational databases to RDF datasets. Such mappings provide the ability to view
    existing relational data in the RDF data model, expressed in a structure and target
    vocabulary of the mapping author's choice.</p>

    <p>This specification has a companion that defines <cite><a class="inform"
    href="http://www.w3.org/TR/2011/WD-rdb-direct-mapping-20110920/">a direct mapping
    from relational databases to RDF</a></cite> [<cite><a href="#DM">DM</a></cite>].
    In the direct mapping of a database, the
    structure of the resulting RDF graph directly reflects the structure of the database,
    the target RDF vocabulary directly reflects the names of database schema elements,
    and neither structure nor target vocabulary can be changed. With R2RML on the other
    hand, a mapping author can define highly customized views over the relational
    data.</p>

    <p>Every R2RML mapping is tailored to a specific database schema and target
    vocabulary. The input to an R2RML mapping is a relational database that conforms to
    that schema. The output is an <cite><a class="norm" href=
    "http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/#rdfDataset">RDF
    dataset</a></cite> [<cite><a href="#SPARQL">SPARQL</a></cite>], as defined in SPARQL,
    that uses predicates and types from the target vocabulary. The mapping is conceptual;
    R2RML processors are free to materialize the output data, or to offer virtual access
    through an interface that queries the underlying database, or to offer any other
    means of providing access to the output RDF dataset.</p>

    <p>R2RML mappings are themselves expressed as RDF graphs and written down in
    <cite><a class="norm" href=
    "http://www.w3.org/TeamSubmission/2008/SUBM-turtle-20080114/">Turtle
    syntax</a></cite> [<cite><a href="#TURTLE">TURTLE</a></cite>].</p>

    <p>The intended audience of this specification is implementors of software
    that
    generates or processes R2RML mapping documents, as well as mapping authors looking
    for a reference to the R2RML language constructs. The document uses concepts from
    <cite><em><a class="norm" href=
    "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">RDF Concepts and Abstract
    Syntax</a></em></cite> [<cite><a href="#RDF">RDF</a></cite>] and from the <cite>SQL
    language specifications</cite> [<cite><a href="#SQL1">SQL1</a></cite>][<cite><a href=
    "#SQL2">SQL2</a></cite>]. A reader's familiarity with the contents of these
    documents, as well as with the Turtle syntax, is assumed.</p>

    <p>The R2RML language is designed to meet the use cases and requirements identified
    in <cite><em><a class="inform" href=
    "http://www.w3.org/TR/2010/WD-rdb2rdf-ucr-20100608/">Use Cases and Requirements for
    Mapping Relational Databases to RDF</a></em></cite> [<cite><a href=
    "#UCNR">UCNR</a></cite>].</p>


    <h3 id="conventions">1.1 Document Conventions</h3>

    <p>In this document, examples assume the following namespace prefix bindings unless
    otherwise stated:</p>

    <table rules="all" summary="list of prefixes used in the document">
      <tr>
        <th>Prefix</th>

        <th>IRI</th>
      </tr>

      <tr>
        <td><code>rr:</code></td>

        <td><code>http://www.w3.org/ns/r2rml#</code></td>
      </tr>

      <tr>
        <td><code>rdf:</code></td>

        <td><code>http://www.w3.org/1999/02/22-rdf-syntax-ns#</code></td>
      </tr>

      <tr>
        <td><code>rdfs:</code></td>

        <td><code>http://www.w3.org/2000/01/rdf-schema#</code></td>
      </tr>

      <tr>
        <td><code>xsd:</code></td>

        <td><code>http://www.w3.org/2001/XMLSchema#</code></td>
      </tr>

      <tr>
        <td><code>ex:</code></td>

        <td><code>http://example.com/ns#</code></td>
      </tr>
    </table>

    <p>Throughout the document, boxes containing Turtle markup and SQL data will appear.
    These boxes are color-coded. Gray boxes contain RDFS definitions of R2RML vocabulary
    terms:</p>
    <pre class="vocab">
# This box contains RDFS definitions of R2RML vocabulary terms
</pre>

    <p>Yellow boxes contain example fragments of R2RML mappings in Turtle syntax:</p>
    <pre class="ex-mapping">
# This box contains example R2RML mappings
</pre>

    <p>Blue tables contain example input into an R2RML mapping:</p>
    <table class="ex-data">
      <caption>EXAMPLE</caption>
      <tr><th>ID <small>INTEGER PRIMARY KEY</small></th><th>DESC <small>VARCHAR(100)</small></th></tr>
      <tr><td>1</td><td>This is an example input table.</td></tr>
      <tr><td>2</td><td>The table name is EXAMPLE.</td></tr>
      <tr><td>3</td><td>It has six rows.</td></tr>
      <tr><td>4</td><td>It has two columns, ID and DESC.</td></tr>
      <tr><td>5</td><td>ID is the table's primary key and of type INTEGER.</td></tr>
      <tr><td>6</td><td>DESC is of type VARCHAR(100)</td></tr>
    </table>

    <p>Green boxes contain example output:</p>

    <pre class="ex-output">
# This box contains example output RDF triples or fragments
</pre>


    <h2 id="overview">2 R2RML Overview and Example (Informative)</h2>

    <p>This section gives a brief overview of the R2RML mapping language,
    followed by a simple example relational database with an
    R2RML mapping document and its output RDF. Further R2RML examples can
    be found in the
    <cite><em><a class="inform" href="http://www.w3.org/2001/sw/rdb2rdf/test-cases/">R2RML and Direct Mapping Test Cases</a></em></cite>
    [<cite><a href="#TC">TC</a></cite>].</p>

    <p>An <a href="#dfn-r2rml-mapping">R2RML mapping</a> refers to
    <a href="#dfn-logical-table">logical tables</a> to retrieve
    data from the <a href="#dfn-input-database">input database</a>.
    A logical table can be one of the following:</p>

    <ol>
      <li>A base table,</li>
      <li>a view, or</li>
      <li>a valid SQL query (called an
      “<a href="#dfn-r2rml-view">R2RML view</a>” because it
      emulates a SQL view without modifying the database).</li>
    </ol>

    <p>Each logical table is mapped to RDF using a
    <a href="#dfn-triples-map">triples map</a>. The triples map is
    a rule that maps each <a href="#dfn-logical-table-row">row in the
    logical table</a> to a number of <a href="#dfn-rdf-triple">RDF triples</a>.
    The rule has two main parts:</p>

    <ol>
    <li>A <a href="#dfn-subject-map">subject map</a> that generates the subject
    of all RDF triples that will be generated from a logical table row.</li>
    <li>Multiple <a href="#dfn-predicate-object-map">predicate-object maps</a>
    that in turn consist of <a href="#dfn-predicate-map">predicate maps</a> and
    <a href="#dfn-object-map">object maps</a>
    (or <a href="#dfn-referencing-object-map">referencing object maps</a>).
    </li>
    </ol>

    <p>Triples are produced by combining the subject map with a predicate
    map and object map, and applying these three to each
    <a href="#dfn-logical-table-row">logical table row</a>. For example, the
    complete rule for generating a set of triples might be:</p>

    <ul>
    <li><strong>Subjects:</strong> A template <code>http://data.example.com/employee/{empno}</code> is used to generate subject <a href="#dfn-iri">IRIs</a> from the <code>empno</code> column.</li>
    <li><strong>Predicates:</strong> The constant vocabulary <a href="#dfn-iri">IRI</a> <code>ex:name</code> is used.</li>
    <li><strong>Objects:</strong> The value of the <code>ename</code> column is used to produce an <a href="#dfn-literal">RDF literal</a>.</li>
    </ul>

    <p>By default, all <a href="#dfn-rdf-triple">RDF triples</a> are in the
    <a href="#dfn-default-graph">default graph</a> of the
    <a href="#dfn-output-dataset">output dataset</a>.
    A triples map can contain
    <a href="#dfn-graph-map">graph maps</a>
    that place some or all of the triples into
    <a href="#dfn-named-graph">named graphs</a> instead.</p>

    <div class="figure">
     <img src="images/uml-overview.png" alt="UML overview diagram of R2RML"/>
      <br /><br />
      Figure 1: An overview of R2RML
    </div>


    <h3 id="example-input-database">2.1 Example Input Database</h3>

    <p>The following example database consists of two tables,
    <code>EMP</code> and <code>DEPT</code>, with one row each:</p>

      <table class="ex-data" summary="EMP table: sample data" id="ex_EMP">
        <caption>EMP</caption>
        <tr>
          <th>EMPNO <small>INTEGER PRIMARY KEY</small></th>
          <th>ENAME <small>VARCHAR(100)</small></th>
          <th>JOB <small>VARCHAR(20)</small></th>
          <th>DEPTNO <small>INTEGER REFERENCES DEPT (DEPTNO)</small></th>
        </tr>
        <tr>
          <td><code>7369</code></td>
          <td><code>SMITH</code></td>
          <td><code>CLERK</code></td>
          <td><code>10</code></td>
        </tr>
      </table>

      <table class="ex-data" summary="DEPT table: sample data" id="ex_DEPT">
        <caption>DEPT</caption>
        <tr>
          <th>DEPTNO <small>INTEGER PRIMARY KEY</small></th>
          <th>DNAME <small>VARCHAR(30)</small></th>
          <th>LOC <small>VARCHAR(100)</small></th>
        </tr>
        <tr>
          <td><code>10</code></td>
          <td><code>APPSERVER</code></td>
          <td><code>NEW YORK</code></td>
        </tr>
      </table>


    <h3 id="desired-rdf">2.2 Desired RDF Output</h3>

    <p>The desired RDF triples to be produced from this database are
    as follows:</p>

    <pre class="ex-output">
&lt;http://data.example.com/employee/7369&gt; rdf:type ex:Employee.
&lt;http://data.example.com/employee/7369&gt; ex:name "SMITH".
&lt;http://data.example.com/employee/7369&gt; ex:department &lt;http://data.example.com/department/10&gt;.

&lt;http://data.example.com/department/10&gt; rdf:type ex:Department.
&lt;http://data.example.com/department/10&gt; ex:name "APPSERVER".
&lt;http://data.example.com/department/10&gt; ex:location "NEW YORK".
&lt;http://data.example.com/department/10&gt; ex:staff 1.</pre>

    <p>Note in particular:</p>

    <ul>
    <li>Construction of custom IRI identifiers for departments and employees;</li>
    <li>use of a custom target vocabulary (<code>ex:Employee</code>, <code>ex:location</code> etc.);</li>
    <li>the <code>ex:staff</code> property has the total number of staff of a department; this value is not stored directly in the database but has to be computed.</li>
    <li>the <code>ex:department</code> property relates an employee to their department, using the identifiers of both entities;</li>
    </ul>


    <h3 id="example-simple">2.3 Example: Mapping a Simple Table</h3>

    <p>The following partial R2RML mapping document will produce
    the desired triples from the <a href="#ex_EMP"><code>EMP</code> table</a>
    (except the
    <code>ex:department</code> triple, which will be added later):</p>

    <pre class="ex-mapping">
@prefix rr: &lt;http://www.w3.org/ns/r2rml#&gt;.

&lt;#TriplesMap1&gt;
    rr:logicalTable [ rr:tableName "EMP" ];
    rr:subjectMap [
        rr:template "http://data.example.com/employee/{EMPNO}";
        rr:class ex:Employee;
    ];
    rr:predicateObjectMap [
        rr:predicate ex:name;
        rr:objectMap [ rr:column "ENAME" ];
    ].</pre>

    <pre class="ex-output">
&lt;http://data.example.com/employee/7369&gt; rdf:type ex:Employee.
&lt;http://data.example.com/employee/7369&gt; ex:name "SMITH".</pre>


    <h3 id="example-r2rml-view">2.4 Example: Computing a Property with an R2RML View</h3>

    <p>Next, the <a href="#ex_DEPT"><code>DEPT</code> table</a> needs 
    to be mapped. Instead of using the table directly as the basis
    for that mapping, an “<a href="#dfn-r2rml-view">R2RML view</a>”
    will be defined based on a SQL query.
    This allows computation of the staff number.
    (Alternatively, one could define this view directly in the database.)</p>

    <pre class="ex-sql">
&lt;#DeptTableView&gt; rr:sqlQuery """
SELECT DEPTNO,
       DNAME,
       LOC,
       (SELECT COUNT(*) FROM EMP WHERE EMP.DEPTNO=DEPT.DEPTNO) AS STAFF
FROM DEPT;
""".
</pre>

    <p>The definition of a triples map that generates the desired
    <code>DEPT</code> triples based on this R2RML view follows.</p>

    <pre class="ex-mapping">
&lt;#TriplesMap2&gt;
    rr:logicalTable &lt;#DeptTableView&gt;;
    rr:subjectMap [
        rr:template "http://data.example.com/department/{DEPTNO}";
        rr:class ex:Department;
    ];
    rr:predicateObjectMap [
        rr:predicate ex:name;
        rr:objectMap [ rr:column "DNAME" ];
    ];
    rr:predicateObjectMap [
        rr:predicate ex:location;
        rr:objectMap [ rr:column "LOC" ];
    ];
    rr:predicateObjectMap [
        rr:predicate ex:staff;
        rr:objectMap [ rr:column "STAFF" ];
    ].</pre>

    <pre class="ex-output">
&lt;http://data.example.com/department/10&gt; rdf:type ex:Department.
&lt;http://data.example.com/department/10&gt; ex:name "APPSERVER".
&lt;http://data.example.com/department/10&gt; ex:location "NEW YORK".
&lt;http://data.example.com/department/10&gt; ex:staff 1.</pre>


    <h3 id="example-fk">2.5 Example: Linking Two Tables</h3>

    <p>To complete the mapping document, the <code>ex:department</code>
    triples need to be generated. Their subjects come from
    the first triples map (<code>&lt;#TriplesMap1&gt;</code>),
    the objects come from the second triples map
    (<code>&lt;#TriplesMap2&gt;</code>).</p>

    <p>This can be achieved by adding another <code>rr:predicateObjectMap</code>
    to <code>&lt;#TriplesMap1&gt;</code>. This one uses the other triples map,
    <code>&lt;#TriplesMap2&gt;</code>, as a <a href="#foreign-key">parent
    triples map</a>:</p>

<pre class="ex-mapping">&lt;#TriplesMap1&gt;
    rr:predicateObjectMap [
        rr:predicate ex:department;
        rr:objectMap [
            rr:parentTriplesMap &lt;#TriplesMap2&gt;;
            rr:joinCondition [
                rr:child "DEPTNO";
                rr:parent "DEPTNO";
            ];
        ];
    ].</pre>

    <p>This performs a join between the <code>EMP</code> table and the
    R2RML view, on the
    <code>DEPTNO</code> columns. The objects will be generated from
    the subject map of the parent triples map, yielding the desired
    triple:</p>

    <pre class="ex-output">
&lt;http://data.example.com/employee/7369&gt; ex:department &lt;http://data.example.com/department/10&gt;.</pre>

    <p>This completes the R2RML mapping document. An R2RML processor will
    generate the triples listed above from this mapping document.</p>


    <h3 id="example-m2m">2.6 Example: Many-to-Many Tables</h3>

    <p>A final example will assume that a many-to-many relationship exists between 
    the extended versions of <a href="#ex_EMP_m2m"><code>EMP</code> table</a> and the <a
    href="#ex_DEPT_m2m"><code>DEPT</code> table</a> shown below. This
    many-to-many relationship is captured by the content of
    the <a href="#ex_EMP2DEPT"><code>EMP2DEPT</code> table</a>. The database consisting of
    the <code>EMP</code>, <code>DEPT</code>, and <code>EMP2DEPT</code> tables are shown below:</p>

      <table class="ex-data" summary="EMP table: sample data" id="ex_EMP_m2m">
        <caption>EMP</caption>
        <tr>
          <th>EMPNO <small>INTEGER PRIMARY KEY</small></th>
          <th>ENAME <small>VARCHAR(100)</small></th>
          <th>JOB <small>VARCHAR(20)</small></th>
          <th>DEPTNO <small>INTEGER REFERENCES DEPT (DEPTNO)</small></th>
        </tr>
        <tr>
          <td><code>7369</code></td>
          <td><code>SMITH</code></td>
          <td><code>CLERK</code></td>
          <td><code>10</code></td>
        </tr>
        <tr>
          <td><code>7369</code></td>
          <td><code>SMITH</code></td>
          <td><code>NIGHTGUARD</code></td>
          <td><code>20</code></td>
        </tr>
        <tr>
          <td><code>7400</code></td>
          <td><code>JONES</code></td>
          <td><code>ENGINEER</code></td>
          <td><code>10</code></td>
        </tr>

      </table>

      <table class="ex-data" summary="DEPT table: sample data" id="ex_DEPT_m2m">
        <caption>DEPT</caption>
        <tr>
          <th>DEPTNO <small>INTEGER PRIMARY KEY</small></th>
          <th>DNAME <small>VARCHAR(30)</small></th>
          <th>LOC <small>VARCHAR(100)</small></th>
        </tr>
        <tr>
          <td><code>10</code></td>
          <td><code>APPSERVER</code></td>
          <td><code>NEW YORK</code></td>
        </tr>
        <tr>
          <td><code>20</code></td>
          <td><code>RESEARCH</code></td>
          <td><code>BOSTON</code></td>
        </tr>
      </table>

      <table class="ex-data" summary="EMP2DEPT table: sample data" id="ex_EMP2DEPT">
        <caption>EMP2DEPT <small>PRIMARY KEY (EMPNO, DEPTNO)</small></caption>
        <tr>
          <th>EMPNO <small>INTEGER REFERENCES EMP (EMPNO)</small></th>
          <th>DEPTNO <small>INTEGER REFERENCES DEPT (DEPTNO)</small></th>
        </tr>
        <tr>
          <td><code>7369</code></td>
          <td><code>10</code></td>
        </tr>
        <tr>
          <td><code>7369</code></td>
          <td><code>20</code></td>
        </tr>
        <tr>
          <td><code>7400</code></td>
          <td><code>10</code></td>
        </tr>
      </table>

    <pre class="ex-output">
&lt;http://data.example.com/employee=7369/department=10&gt; 
    ex:employee   &lt;http://data.example.com/employee/7369&gt; ;
    ex:department &lt;http://data.example.com/department/10&gt; .

&lt;http://data.example.com/employee=7369/department=20&gt; 
    ex:employee &lt;http://data.example.com/employee/7369&gt; ;
    ex:department &lt;http://data.example.com/department/20&gt; .

&lt;http://data.example.com/employee=7400/department=10&gt; 
    ex:employee &lt;http://data.example.com/employee/7400&gt; ;
    ex:department &lt;http://data.example.com/department/10&gt; .
    </pre>

    <p>The following R2RML mapping will produce the desired triples listed above:</p>

    <pre class="ex-mapping">&lt;#TriplesMap3&gt;
    rr:tableName "EMP2DEPT";
    rr:subjectMap [ rr:template "http://data.example.com/employee={EMPNO}/department={DEPTNO}" ];
    rr:predicateObjectMap [
        rr:predicate ex:employee;
        rr:objectMap [ rr:template "http://data.example.com/employee/{EMPNO}" ; rr:termType rr:IRI ]
    ];
    rr:predicateObjectMap [
        rr:predicate ex:department;
        rr:objectMap [ rr:template "http://data.example.com/department/{DEPTNO}" ; rr:termType rr:IRI ]
    ].
    </pre>


    <p>However, if one does <em>not</em> require that the subjects in
    the desired output uniquely identify the rows in the <a
    href="#ex_EMP2DEPT"><code>EMP2DEPT</code> table</a>, the desired output
    may look as follows: </p>

    <pre class="ex-output">
&lt;http://data.example.com/employee/7369&gt; 
    ex:department &lt;http://data.example.com/department/10&gt; ;
    ex:department &lt;http://data.example.com/department/20&gt; .

&lt;http://data.example.com/employee/7400&gt; 
    ex:department &lt;http://data.example.com/department/10&gt;.
    </pre>

    <p>The following R2RML mapping will produce the desired triples:</p>

    <pre class="ex-mapping">&lt;#TriplesMap3&gt;
    rr:tableName "EMP2DEPT";
    rr:subjectMap [
        rr:template "http://data.example.com/employee/{EMPNO}";
    ];
    rr:predicateObjectMap [
      rr:predicate ex:department;
      rr:objectMap [ rr:template "http://data.example.com/department/{DEPTNO}"; rr:termType rr:IRI ]
    ].</pre>


    <h2 id="conformance">3 Conformance</h2>

    <p>As well as sections marked as non-normative in the section heading,
    all diagrams, examples, and notes in this specification are
    non-normative. Everything else in this specification is normative.</p>

    <p>The key words <em class="rfc2119">must</em>,
    <em class="rfc2119">must not</em>, <em class="rfc2119">required</em>,
    <em class="rfc2119">should</em>, <em class="rfc2119">should not</em>,
    <em class="rfc2119">recommended</em>, <em class="rfc2119">may</em>,
    and <em class="rfc2119">optional</em> in this specification are to be
    interpreted as described in
    <cite><a href="http://tools.ietf.org/html/rfc2119">RFC 2119</a></cite>
    [<cite><a href="#RFC2119">RFC2119</a></cite>].</p>

    <p>This specification describes conformance criteria for:</p>

    <ul>
    <li><a href="#dfn-r2rml-mapping-document">R2RML mapping documents</a></li>
    <li><a href="#dfn-r2rml-mapping-graph">R2RML mapping graphs</a></li>
    <li><a href="#dfn-r2rml-processor">R2RML processors</a></li>
    <li><a href="#dfn-r2rml-data-validator">R2RML data validators</a></li>
    </ul>

    <p>A collection of test cases for R2RML processors and
    R2RML data validators is available in the
    <cite><em><a class="inform" href="http://www.w3.org/2001/sw/rdb2rdf/test-cases/">R2RML and Direct Mapping Test Cases</a></em></cite> [<cite><a href="#TC">TC</a></cite>].</p>

    <p>This specification defines R2RML for databases that conform to
    <em>Core SQL 2008</em>, as defined in
    <cite><em>ISO/IEC 9075-1:2008</em></cite>
    [<cite><a href="#SQL1">SQL1</a></cite>] and
    <cite><em>ISO/IEC 9075-2:2008</em></cite>
    [<cite><a href="#SQL2">SQL2</a></cite>].
    Processors and mappings may have
    to deviate from the R2RML specification in order to support databases
    that do not conform to this version of SQL.</p>

    <p>Where SQL queries are embedded into R2RML mappings,
    <a href="#dfn-sql-version-identifier">SQL version identifiers</a>
    can be used to indicate the specific version of SQL that is being used.</p>


    <h2 id="definitions">4 R2RML Processors and Mapping Documents</h2>

    <p>An <dfn id="dfn-r2rml-mapping">R2RML mapping</dfn> defines a mapping
    from a relational database to RDF. It is a structure that consists of
    one or more <a href="#dfn-triples-map">triples maps</a>.</p>

    <p>The input to an R2RML mapping is called the
    <dfn id="dfn-input-database">input database</dfn>.</p>

    <p>An <dfn id="dfn-r2rml-processor">R2RML processor</dfn> is a system
    that, given an <a href="#dfn-r2rml-mapping">R2RML mapping</a> and an
    <a href="#dfn-input-database">input database</a>, provides access to 
    the <a href="#dfn-output-dataset">output dataset</a>.</p>

    <p>There are no constraints on the method of access to the output
    dataset provided by a conforming R2RML processor. An R2RML processor
    <em class="rfc2119">MAY</em>
    materialize the output dataset into a file, or offer virtual access
    through an interface that queries the input database, or offer any
    other means of providing access to the output dataset.</p>

    <p>An <a href="#dfn-r2rml-processor">R2RML processor</a> also has access
    to an execution environment consisting of:</p>

    <ul>
    <li>A <dfn id="dfn-sql-connection">SQL connection</dfn>
    to the <a href="#dfn-input-database">input database</a>,</li>
    <li>a <dfn id="dfn-base-iri">base IRI</dfn> used in resolving
    relative IRIs produced by the R2RML mapping.</li>
    </ul>

    <p>The <a href="#dfn-sql-connection">SQL connection</a> 
    is used by the R2RML processor to evaluate SQL queries against the input
    database. It <em class="rfc2119">MUST</em> be established
    with sufficient privileges for read access to all base tables and views that are
    referenced in the R2RML mapping. It <em class="rfc2119">MUST</em> be
    configured with a <dfn id="dfn-default-catalog">default catalog</dfn>
    and <dfn id="dfn-default-schema">default schema</dfn> that will be
    used when tables and views are accessed without an explicit
    catalog or schema reference.</p>

    <p>How the SQL connection is established, or how users
    are authenticated against the database, is outside of the scope of this document.</p>

    <p>The <a href="#dfn-base-iri">base IRI</a> <em class="rfc2119">MUST</em>
    be a valid <a href="#dfn-iri">IRI</a>. It <em class="rfc2119">SHOULD</em>
    end in a slash (“<code>/</code>”) character.</p>

    <p class="note">Resolution of relative IRIs in R2RML uses simple
    string concatenation instead of the more complex algorithm defined in
    RFC 3986. This ensures that the original database value can be
    reconstructed from the generated IRI.</p>

    <p>An <dfn id="dfn-r2rml-data-validator">R2RML data validator</dfn>
    is a system that takes as its input an
    <a href="#dfn-r2rml-mapping">R2RML mapping</a>, a
    <a href="#dfn-base-iri">base IRI</a>, and a
    <a href="#dfn-sql-connection">SQL connection</a> to an
    <a href="#dfn-input-database">input database</a>, and checks for
    the presence of <a href="#dfn-data-error">data errors</a>.
    When checking the input database, a data validator
    <em class="rfc2119">MUST</em> report any data errors that are raised
    in the process of generating the output dataset.</p>

    <p>An <a href="#dfn-r2rml-processor">R2RML processor</a>
    <em class="rfc2119">MAY</em> include an
    <a href="#dfn-r2rml-data-validator">R2RML data validator</a>, but this
    is not required.</p>


    <h3 id="vocabulary">4.1 Mapping Graphs and the R2RML Vocabulary</h3>

    <p>An <a href="#dfn-r2rml-mapping">R2RML mapping</a> is represented
    as an <a href="#dfn-rdf-graph">RDF graph</a>. In other words,
    RDF is used not just as the target data model of the mapping, but also
    as a formalism for representing the R2RML mapping itself.</p>

    <p>An <a href="#dfn-rdf-graph">RDF graph</a> that represents an
    <a href="#dfn-r2rml-mapping">R2RML mapping</a> is called an
    <dfn id="dfn-r2rml-mapping-graph">R2RML mapping graph</dfn>.</p>

    <p>The <dfn id="dfn-r2rml-vocabulary">R2RML vocabulary</dfn> is the
    set of <a href="#dfn-iri">IRIs</a> defined in this specification
    that start with the <code>rr:</code> namespace IRI:</p>

    <pre><strong><a href="http://www.w3.org/ns/r2rml#">http://www.w3.org/ns/r2rml#</a></strong></pre>

    <p>An <a href="#dfn-r2rml-mapping-graph">R2RML mapping graph</a>:</p>

    <ul>
    <li><em class="rfc2119">SHOULD NOT</em> include any
    <a href="#dfn-iri">IRIs</a> that start with the <code>rr:</code>
    namespace IRI, but are not defined in the
    <a href="#dfn-r2rml-vocabulary">R2RML vocabulary</a>.</li>

    <li><em class="rfc2119">SHOULD NOT</em> include
    <a href="#dfn-iri">IRIs</a> from the
    <a href="#dfn-r2rml-vocabulary">R2RML vocabulary</a> where
    such use is not explicitly allowed or required by a clause in this
    specification.</li>

    <li><em class="rfc2119">SHOULD NOT</em> contain any
    mapping components (<a href="#dfn-logical-table">logical tables</a>,
    <a href="#dfn-term-map">term maps</a>,
    <a href="#dfn-predicate-object-map">predicate-object maps</a>)
    that are not referenced by a <a href="#dfn-triples-map">triples map</a>
    (in other words, are “unused”).</li>

    <li><em class="rfc2119">MAY</em> contain arbitrary additional
    <a href="#dfn-rdf-triple">triples</a> whose terms are not 
    from the <a href="#dfn-r2rml-vocabulary">R2RML vocabulary</a>.
    In particular, a valid mapping graph <em class="rfc2119">MAY</em>
    contain documentation in the form of <code>rdfs:label</code>,
    <code>rdfs:comment</code> and similar properties.</li>

    <li><em class="rfc2119">MAY</em> assign <a href="#dfn-iri">IRIs</a>
    or <a href="#dfn-blank-node-identifier">blank node identifiers</a>
    to any mapping component in order to enable re-use of mapping components
    within the mapping graph.
    For example, an IRI that represents
    a <a href="#dfn-subject-map">subject map</a> may be used as the subject 
    map of multiple <a href="#dfn-triples-map">triples maps</a>; and may
    even be used as an <a href="#dfn-object-map">object map</a> of another
    triples map if it has the right properties.</li>
    </ul>

    <p>The <a href="#dfn-r2rml-vocabulary">R2RML vocabulary</a> also
    includes the following <dfn id="dfn-R2RML-classes">R2RML classes</dfn>,
    which represent various R2RML mapping constructs. Using these
    classes is <em class="rfc2119">OPTIONAL</em> in a mapping graph.
    The applicable class of a resource can always be inferred from its
    properties.</p>

    <ul>
      <li><code>rr:TriplesMap</code> is the class of
      <a href="#dfn-triples-map">triples maps</a>.</li>
      <li><code>rr:LogicalTable</code> is the class of
      <a href="#dfn-logical-table">logical tables</a>.</li>
      <li><code>rr:SubjectMap</code> is the class of
      <a href="#dfn-subject-map">subject maps</a>.</li>
      <li><code>rr:PredicateMap</code> is the class of
      <a href="#dfn-predicate-map">predicate maps</a>.</li>
      <li><code>rr:ObjectMap</code> is the class of
      <a href="#dfn-object-map">object maps</a>.</li>
      <li><code>rr:GraphMap</code> is the class of
      <a href="#dfn-graph-map">graph maps</a>.</li>
      <li><code>rr:PredicateObjectMap</code> is the class of
      <a href="#dfn-predicate-object-map">predicate-object maps</a>.</li>
      <li><code>rr:RefObjectMap</code> is the class of
      <a href="#dfn-referencing-object-map">referencing object maps</a>.</li>
      <li><code>rr:Join</code> is the class of
      <a href="#dfn-join-condition">join conditions</a>.</li>
    </ul>

    <p class="note">Many of these classes differ only in capitalization from
    properties in the <a href="#dfn-r2rml-vocabulary">R2RML vocabulary</a>.</p>


    <h3 id="syntax">4.2 RDF-based Turtle Syntax; Media Type</h3>

    <div class="issue">
    <p><a class="tracker" href="http://www.w3.org/2001/sw/rdb2rdf/track/issues/57">ISSUE-57</a>:
    <strong>Should R2RML require a specific syntax?</strong></p>

    <p>The working group has proposed two alternate proposals for this issue:</p>

    <ol>   
    <li>The R2RML mapping document specifies both the vocabulary and
    the syntax.  The R2RML document <em class="rfc2119">MUST</em> be a Turtle document and
    R2RML processors <em class="rfc2119">MUST</em> support Turtle to be able to read such
    documents. Conformance criteria requires support of R2RML
    vocabulary written in Turtle.</li>

    <li>The R2RML mapping document specifies only the
    vocabulary. There is no syntax specified.  There can be an
    accompanying "R2RML mapping document in Turtle" that specifies the
    Turtle syntax.  Conformance criteria for the R2RML mapping
    document requires supporting the vocabulary in any language
    (Turtle, N-Triple, RDF/XML etc.)  Additionally, if an
    implementation supports the Turtle syntax, it can claim
    conformance to the "R2RML mapping document in Turtle".</li>
    </ol>

    <p>The advantage of the first approach is that it promotes
    interoperability between different producers and consumers of
    R2RML files by requiring all to support at least one shared
    syntax. Without such a shared syntax, an R2RML file created in one
    tool may be rejected by another tool because both assume different
    RDF syntaxes. R2RML examples found in educational material may not
    work in actual implementations due to different syntaxes. This is
    seen as an impediment to the uptake of R2RML.
    </p>

    <p>The second approach distinguishes between the R2RML vocabulary
    and the syntax and wants to keep them separate.  The advantage of
    the second approach is that the R2RML mapping document remains
    independent of any exchange format.  This gives flexibility as
    different syntax flavours of R2RML could be easily defined. It is
    in the spirit of RDF as an abstract format. Users may have to
    convert between different RDF syntaxes in order to use R2RML
    files, but such conversion is not difficult and therefore not seen
    as an impediment. Thereby, it allows conformance with the R2RML
    mapping document using any of the standard exchange formats.
    </p>

    <p>There is consensus that Turtle should be used for the examples in
    this document, as well as for the test cases.</p>

    <p>The working group seeks comments and opinions on this question
    and encourages reports to <a href="http://lists.w3.org/Archives/Public/public-rdb2rdf-comments/">public-rdb2rdf-comments mailing list</a>.</p>
    </div>

    <p>An <dfn id="dfn-r2rml-mapping-document">R2RML mapping document</dfn> is any document
    written in the <cite><a class="norm" href=
    "http://www.w3.org/TeamSubmission/2008/SUBM-turtle-20080114/">Turtle</a></cite>
    [<cite><a href="#TURTLE">TURTLE</a></cite>] RDF syntax that encodes an
    <a href="#dfn-r2rml-mapping-graph">R2RML mapping graph</a>.</p>

    <p>The media type for <a href="#dfn-r2rml-mapping-document">R2RML mapping
    documents</a> is the same as for Turtle
    documents in general: <code>text/turtle</code>. The content encoding of
    Turtle content is always UTF-8 and the <code>charset</code> parameter
    on the media type <em class="rfc2119">SHOULD</em> always be used:
    <code>text/turtle;charset=utf-8</code>. The preferred file extension is
    <code>.ttl</code>.</p>

    <p>A conforming <a href="#dfn-r2rml-processor">R2RML processor</a>
    <em class="rfc2119">MUST</em> accept <a href="#dfn-r2rml-mapping-document">
    R2RML mapping documents</a> in Turtle syntax.
    It <em class="rfc2119">MAY</em> accept
    <a href="#dfn-r2rml-mapping-graph">R2RML mapping graphs</a> encoded in
    other RDF syntaxes.</p>

    <div class="note">
    <p>It is common to use document-local IRIs in mapping documents by
    defining the default prefix in the beginning of the document, and
    using it for creating IRIs for mapping components such as triples maps:</p>
    <pre>@prefix : &lt;#&gt;
…
:EmpQuery rr:sqlQuery """SELECT * FROM EMP WHERE …""".
…
:EmpTriples rr:logicalTable :EmpQuery.</pre>
    </div>


    <h3 id="data-errors">4.3 Data Errors</h3>

    <p>A <dfn id="dfn-data-error">data error</dfn> is a condition
    of the data in the <a href="#dfn-input-database">input database</a>
    that would lead to the generation of an invalid
    <a href="#dfn-rdf-term">RDF term</a>, such as an invalid
    <a href="#dfn-iri">IRI</a> or an ill-typed
    <a href="#dfn-literal">literal</a>.</p>

    <p>When providing access to the
    <a href="#dfn-output-dataset">output dataset</a>, an
    <a href="#dfn-r2rml-processor">R2RML processor</a>
    <em class="rfc2119">MUST</em> abort any operation that
    requires inspecting or returning an <a href="#dfn-rdf-term">RDF term</a>
    whose generation would give rise to a
    <a href="#dfn-data-error">data error</a>, and report an error
    to the agent invoking the operation. A conforming
    <a href="#dfn-r2rml-processor">R2RML processor</a>
    <em class="rfc2119">MAY</em>, however, allow other operations
    that do not require inspecting or returning these
    <a href="#dfn-rdf-term">RDF terms</a>,
    and thus <em class="rfc2119">MAY</em> provide partial access to an
    <a href="#dfn-output-dataset">output dataset</a> that contains
    data errors. Nevertheless, an
    <a href="#dfn-r2rml-processor">R2RML processor</a>
    <em class="rfc2119">SHOULD</em> report data errors as early as possible.</p>

    <p>The following conditions give rise to data errors:</p>

    <ol>
    <li>A <a href="#dfn-term-map">term map</a> with
    <a href="#dfn-term-type">term type</a> <code>rr:IRI</code>
    results in the <a href="#dfn-generated-rdf-terms">generation</a>
    of an invalid <a href="#dfn-iri">IRI</a>.</li>
    <li>A <a href="#dfn-term-map">term map</a> with a
    <a href="#dfn-datatype-override">datatype override</a>
    produces an <a href="#dfn-ill-typed">ill-typed</a> literal
    of a <a href="#dfn-supported-rdf-datatype">supported RDF datatype</a>.</li>
    </ol>

    <p>The presence of <a href="#dfn-data-error">data errors</a>
    does not make an <a href="#dfn-r2rml-mapping">R2RML mapping</a>
    non-conforming.</p>

    <div class="note">
    <p><a href="#dfn-data-error">Data errors</a> cannot
    generally be detected by analyzing the table schema of the database,
    but only by scanning the data in the tables. For large and rapidly
    changing databases, this can be impractical. Therefore,
    <a href="#dfn-r2rml-processor">R2RML processors</a> are allowed to
    answer queries that do not “touch” a data error, and the behavior
    of such operations is well-defined. For the same reason,
    the conformance of <a href="#dfn-r2rml-mapping">R2RML mappings</a>
    is defined without regard for the presence of data errors.</p>

    <p><a href="#dfn-r2rml-data-validator">R2RML data validators</a>
    can be used to explicitly scan a database for data errors.</p>
    </div>


    <h2 id="logical-tables">5 Defining Logical Tables</h2>

    <div class="figure">
     <img src="images/logical-table.png" alt="Diagram: The properties of logical tables"/>
      <br /><br />
      Figure 2: The properties of logical tables
    </div>

    <p>A <dfn id="dfn-logical-table">logical table</dfn> is a
    possibly virtual database table that is to be mapped to
    <a href="#dfn-rdf-triple">RDF triples</a>. A logical table is either</p>

    <ul>
    <li>a <a href="#dfn-sql-base-table-or-view">SQL base table or view</a>,
    or</li>
    <li>a <a href="#dfn-r2rml-view">R2RML view</a>.</li>
    </ul>

    <p>Every logical table has an
    <dfn id="dfn-effective-sql-query">effective SQL query</dfn> that,
    if executed over the <a href="#dfn-sql-connection">SQL connection</a>,
    produces as its result the contents of the logical table.</p>

    <p>A <dfn id="dfn-logical-table-row">logical table row</dfn> is a row
    in a <a href="#dfn-logical-table">logical table</a>.</p>

    <p>A <dfn id="dfn-column-name">column name</dfn> is the name of a
    column of a <a href="#dfn-logical-table">logical table</a>. A column name
    <em class="rfc2119">MUST</em> be a valid
    <a href="#dfn-sql-identifier">SQL identifier</a>. Column names
    do not include any qualifying table, view or schema names.</p>

    <p>A <dfn id="dfn-sql-identifier">SQL identifier</dfn> is the name of
    a SQL object, such as a column, table, view, schema, or catalog.
    A SQL identifier
    <em class="rfc2119">MUST</em> match the <code>&lt;identifier&gt;</code>
    production in [<cite><a href="#SQL2">SQL2</a></cite>].  When
    comparing identifiers for equality, the comparison rules
    of [<cite><a href="#SQL2">SQL2</a></cite>] <em class="rfc2119">MUST</em>
    be used.</p>

    <div class="note">
    An informative summary of SQL identifier syntax rules:
    <ol>
    <li>SQL identifiers can be delimited identifiers (with double quotes),
    or regular identifiers.</li>
    <li>Regular identifiers must start with a Unicode character from
    any of the following character classes: upper-case letter,
    lower-case letter, title-case letter, modifier letter, other letter,
    or letter number. Subsequent characters may be any of these, or
    a nonspacing mark, spacing combining mark, decimal number,
    connector punctuation, and formatting code.</li>
    <li>Regular identifiers are case-insensitive.</li>
    <li>Delimited identifiers can contain any character.</li>
    <li>Double quotes inside delimited identifiers must be immediately
    followed by another double quote.</li>
    <li>Delimited identifiers are case-sensitive.</li>
    <li><code>deptno</code> and <code>"deptno"</code> are not equivalent
    (delimited identifiers that are not in all-upper-case are
    not equivalent to any undelimited identifiers).</li>
    <li><code>DEPTNO</code> and <code>"DEPTNO"</code> are equivalent
    (all-upper-case delimited and undelimited identifiers are equivalent).</li>
    <li>Five examples of valid column names:
    <code>deptno</code>, <code>dept_no</code>, <code>"dept_no"</code>,
    <code>"Department Number"</code>,
    <code>"Identifier ""with quotes"""</code>.</li>
    </ol>

    Note that in R2RML, column name specified as an RDF <a
    href="#dfn-plain-literal">plain literal</a> or within curly
    braces, is considered a delimited SQL identifier.  Thus the SQL column
    name identifiers <code>deptno</code>, <code>dept_no</code>,
    <code>"dept_no"</code>, <code>"Department Number"</code> can be
    used as (part of) object value for the various relevant R2RML properties
    as follows:

    <pre>
[] rr:column "DEPTNO".
[] rr:parent "DEPT_NO".
[] rr:child "dept_no".
[] rr:template "http://data.example.com/department/{Department Number}".
    </pre>

    Note that Turtle string syntax requires escaping of double quotes with
    a backslash, so the identifier <code>"Identifier ""with quotes"""</code> can be
    used as (part of) value for the various relevant R2RML properties as follows:
    <pre>
[] rr:column "Identifier \"\"with quotes\"\"".
[] rr:template "http://data.example.com/department/{Identifier \"\"with quotes\"\"}".
</pre>
    These rules are for <em>Core SQL 2008</em>. See
    <a href="#conformance">Section 3,
    <em>Conformance</em></a> regarding databases that do not conform to this
    version of SQL.
    </div>


    <h3 id="physical-tables">5.1 Base Tables and SQL Views (<code>rr:tableName</code>)</h3>

    <p>A <dfn id="dfn-sql-base-table-or-view">SQL base table or view</dfn> is a
    <a href="#dfn-logical-table">logical table</a> containing
    SQL data from a base table or view in the
    <a href="#dfn-input-database">input database</a>.
    A SQL base tables or views is represented by a resource that
    has exactly one <code>rr:tableName</code> property.</p>

    <p>The value of <code>rr:tableName</code> specifies the
    <dfn id="dfn-table-or-view-name">table or view name</dfn> of the base table or view.
    Its value <em class="rfc2119">MUST</em>
    be a valid <a href="#dfn-schema-qualified-name">schema-qualified name</a>
    that names an existing base table or view in the
    <a href="#dfn-input-database">input database</a>.</p>

    <p>A <dfn id="dfn-schema-qualified-name">schema-qualified name</dfn>
    is a sequence of one, two or three valid
    <a href="#dfn-sql-identifier">SQL identifiers</a>, separated
    by the dot character (“<code>.</code>”). The three identifiers
    name, respectively, a catalog, a schema, and a table or view.
    If no catalog or schema are specified, then the
    <a href="#dfn-default-catalog">default catalog</a> and
    <a href="#dfn-default-schema">default schema</a> of the
    <a href="#dfn-sql-connection">SQL connection</a> are assumed.</p>

    <p>The <a href="#dfn-effective-sql-query">effective SQL query</a>
    of a <a href="#dfn-sql-base-table-or-view">SQL base table or view</a> is:</p>

    <pre>SELECT * FROM <em>{table}</em></pre>
    <p>with <code><em>{table}</em></code>
    replaced with the
    <a href="#dfn-table-or-view-name">table or view name</a>.</p>

    <p>The following example shows a logical table specified using 
    a schema-qualified table name.</p>
    <pre class="ex-mapping">
[] rr:tableName "SCOTT.DEPT".
</pre>

    <p>The following example shows a logical table specified using 
    an unqualified table name. The SQL connection's default
    schema will be used.</p>
    <pre class="ex-mapping">
[] rr:tableName "DEPT".
</pre>


    <h3 id="r2rml-views">5.2 R2RML Views (<code>rr:sqlQuery</code>, <code>rr:sqlVersion</code>)</h3>

    <p>An <dfn id="dfn-r2rml-view">R2RML view</dfn>
    is a <a href="#dfn-logical-table">logical table</a> whose contents
    are the result of executing a SQL query against the
    <a href="#dfn-input-database">input database</a>. It is represented
    by a resource that has exactly one <code>rr:sqlQuery</code> property,
    whose value <em class="rfc2119">MUST</em> be a valid
    <a href="#dfn-sql-query">SQL query</a>.</p>

    <p class="note">
    R2RML mappings sometimes require data transformation, computation,
    or filtering before
    generating triples from the database. This can be achieved by defining
    a SQL view in the <a href="#dfn-input-database">input database</a>
     and referring to it with
    <a href="#dfn-sql-base-table-or-view">rr:tableName</a>. However, this
    approach may not be practical for lack of database privileges or other
    reasons. <a href="#dfn-r2rml-view">R2RML views</a>
    achieve the same effect without requiring changes to the
    input database.</p>

    <p class="note">
    Note that unlike “real” SQL views, an R2RML view can not be
    used as an input table in further SQL queries.
    </p>

    <p>A <dfn id="dfn-sql-query">SQL query</dfn> is a <code>SELECT</code>
    query in the SQL language that can be executed over the
    <a href="#dfn-input-database">input database</a>.
    The value of <code>rr:sqlQuery</code> <em class="rfc2119">MUST</em>
    conform to the production
    <code>&lt;direct select statement: multiple rows&gt;</code>
    in [<cite><a href="#SQL2">SQL2</a></cite>] with an
    <em class="rfc2119">OPTIONAL</em> trailing semicolon character and
    <em class="rfc2119">OPTIONAL</em> surrounding white space (excluding
    comments) as defined in [<cite><a href="#TURTLE">TURTLE</a></cite>].
    It <em class="rfc2119">MUST</em> be a valid SQL query if executed over
    the <a href="#dfn-sql-connection">SQL connection</a>. It
    <em class="rfc2119">MUST NOT</em> have duplicate column names
    or unnamed derived columns in the <code>SELECT</code> list. For any
    database objects referenced without an explicit catalog name
    or schema name, the <a href="#dfn-default-catalog">default catalog</a>
    and <a href="#dfn-default-schema">default schema</a> of the
    <a href="#dfn-sql-connection">SQL connection</a> are used.</p>

    <p>An <a href="#dfn-r2rml-view">R2RML view</a>
    <em class="rfc2119">MAY</em> have one or more
    <dfn id="dfn-sql-version-identifier">SQL version identifiers</dfn>.
    They <em class="rfc2119">MUST</em> be valid <a href="#dfn-iri">IRIs</a>
    and are represented as values of the <code>rr:sqlVersion</code>
    property. The following <a href="#dfn-sql-version-identifier">SQL version
    identifier</a> indicates that the SQL query conforms to
    Core SQL 2008:</p>

    <pre>http://www.w3.org/ns/r2rml#SQL2008</pre>

    <p>The absence of a <a href="#dfn-sql-version-identifier">SQL version
    identifier</a> indicates that no claim to Core SQL 2008 conformance
    is made.</p>

    <p class="note">No further identifiers besides <code>rr:SQL2008</code>
    are defined in this specification.
    The RDB2RDF Working Group intends to maintain a non-normative
    <cite><a href="http://www.w3.org/2001/sw/rdb2rdf/wiki/SQL_Version_IRIs">list
    of identifiers for other SQL versions</a></cite>
    [<cite><a href="#SQLIRIS">SQLIRIS</a></cite>].</p>

    <p>The <a href="#dfn-effective-sql-query">effective SQL query</a>
    of an <a href="#dfn-r2rml-view">R2RML view</a> is the value of its
    <code>rr:sqlQuery</code> property.</p>

    <p>The following example shows a logical table specified as an R2RML view
    conforming to Core SQL 2008.</p>
    <pre class="ex-mapping">
[] rr:sqlQuery """
        Select ('Department' || DEPTNO) AS DEPTID
             , DEPTNO
             , DNAME
             , LOC
          from SCOTT.DEPT
    """;
    rr:sqlVersion rr:SQL2008.</pre>


    <h2 id="triples-map">6 Mapping Logical Tables to RDF with Triples Maps</h2>

    <div class="figure">
     <img src="images/triples-map.png" alt="Diagram: The properties of triples maps"/>
      <br /><br />
      Figure 3: The properties of triples maps
    </div>

    <p>A <dfn id="dfn-triples-map">triples map</dfn> specifies a rule
    for translating each row of a <a href="#dfn-logical-table">logical table</a>
    to zero or more <a href="#dfn-rdf-triple">RDF triples</a>.</p>

    <p>The RDF triples generated from one row in the logical table
    all share the same subject.</p>

    <p>A triples map is represented by a resource that references the
    following other resources:</p>

    <ul>
    <li>It <em class="rfc2119">MUST</em> have exactly one
    <a href="#dfn-logical-table">logical table</a>,
    which specifies a SQL query result to be mapped to triples.
    The logical table may be specified in one of two ways:
      <ol>
      <li>The <a href="#dfn-triples-map">triples map</a>
      <em class="rfc2119">MAY</em> have a <code>rr:logicalTable</code>
      property, whose value <em class="rfc2119">MUST</em> be
      the <a href="#dfn-logical-table">logical table</a>.</li>
      <li>The resource representing the
      <a href="#dfn-triples-map">triples map</a>
      <em class="rfc2119">MAY</em> itself also represent
      the <a href="#dfn-logical-table">logical table</a>
      (that is, have the required properties such as
      <code>rr:tableName</code> or <code>rr:sqlQuery</code>).</li>
      </ol>
    </li>

    <li>It <em class="rfc2119">MUST</em> have exactly one
    <a href="#dfn-subject-map">subject map</a>
    that specifies how to generate the subjects for each row of the
    logical table. It may be specified in two ways:
      <ol>
      <li>using the <code>rr:subjectMap</code> property,
      whose value <em class="rfc2119">MUST</em> be
      the subject map, or</li>
      <li>using the <a href="#dfn-constant-shortcut-property">constant
      shortcut property</a> <code>rr:subject</code>.</li>
      </ol>
    </li>

    <li>It <em class="rfc2119">MAY</em> have zero or more
    <code>rr:predicateObjectMap</code> properties,
    whose values <em class="rfc2119">MUST</em> be
    <a href="#dfn-predicate-object-map">predicate-object maps</a>.
    Each specifies a predicate-object pair that, together with the
    subjects generated by the subject map, may form one
    <a href="#dfn-rdf-triple">RDF triple</a> for each row.</li>
    </ul>
    
    <p>The <a href="#dfn-referenced-columns">referenced columns</a> of
    all <a href="#dfn-term-map">term maps</a> of a triples map
    (subject map, predicate maps, object maps, graph maps)
    <em class="rfc2119">MUST</em>
    be <a href="#dfn-column-name">column names</a> that exist
    in the term map's <a href="#dfn-logical-table">logical table</a>.
    Furthermore, the columns carrying these names in the
    logical table <em class="rfc2119">MUST</em> be of a SQL datatype
    for which <a href="#dfn-conversion-to-string">conversion to string</a>
    is defined.</p>

    <p class="note"><a href="#dfn-conversion-to-string">Conversion
    to string</a> is undefined in SQL 2008 for row types, array types,
    user-defined datatypes that do not have a user-defined string
    <code>CAST</code>, and a few other exotic types.</p>

    <p>The following example shows a <a href="#dfn-triples-map">triples map</a>
    including its logical table, subject map, and two predicate-object maps.</p>

    <pre class="ex-mapping">
[]
    rr:logicalTable [ rr:tableName "DEPT" ];
    rr:subjectMap [ rr:template "http://data.example.com/department/{DEPTNO}" ];
    rr:predicateObjectMap [
        rr:predicate ex:name;
        rr:objectMap [ rr:column "DNAME" ];
    ].
    rr:predicateObjectMap [
        rr:predicate ex:location;
        rr:objectMap [ rr:column "LOC" ];
    ].</pre>

    <p>The logical table may also be specified directly on the same
    resource, without introducing an intermediate resource:</p>

    <pre class="ex-mapping">
[]
    rr:tableName "DEPT";
    rr:subjectMap [ rr:template "http://data.example.com/department/{DEPTNO}" ];
    # …
    .</pre>

    <h3 id="subject-map">6.1 Creating Resources with Subject Maps</h3>

    <p>A <dfn id="dfn-subject-map">subject map</dfn> is a
    <a href="#dfn-term-map">term map</a>. It specifies a rule
    for generating the subjects of the
    <a href="#dfn-rdf-triple">RDF triples</a> generated by a
    <a href="#dfn-triples-map">triples map</a>.</p>


    <h3 id="typing">6.2 Typing Resources (<code>rr:class</code>)</h3>

    <p>A <a href="#dfn-subject-map">subject map</a> <em class="rfc2119">MAY</em>
    have one or more <dfn id="dfn-class-iri">class IRIs</dfn>. They are
    represented by the <code>rr:class</code> property. The values
    of the <code>rr:class</code> property
    <em class="rfc2119">MUST</em> be <a href="#dfn-iri">IRIs</a>.
    For each <a href="#dfn-rdf-term">RDF term</a> generated by the subject map,
    <a href="#dfn-rdf-triple">RDF triples</a> with predicate
    <code>rdf:type</code> and the class IRI as object will be generated.</p>

    <p class="note">This property is merely a shortcut for specifying an
    <code>rr:predicateObjectMap</code> with predicate <code>rdf:type</code>
    and the <code>rr:class</code> IRI as a constant object.
    Mappings where the class IRI is not constant, but needs to be computed
    based on the contents of the database, can be achieved by defining
    such a <code>rr:predicateObjectMap</code> with a non-constant object.</p>

    <p>In the following example, the generated subject will be asserted
    as an instance of the <code>ex:Employee</code> class.</p>
    <pre class="ex-mapping">
[] rr:template "http://data.example.com/employee/{EMPNO}"; 
   rr:class ex:Employee.
</pre>

    <p>Using the example <a href="#ex_EMP"><code>EMP</code> table</a>,
    the following RDF triple will be generated:</p>
    <pre class="ex-output">
&lt;http://data.example.com/emp/7369&gt; rdf:type ex:Employee.
</pre>


    <h3 id="predicate-object-map">6.3 Creating Properties and Values with Predicate-Object Maps</h3>

    <p>A <dfn id="dfn-predicate-object-map">predicate-object map</dfn> is
    a function that creates predicate-object pairs from
    <a href="#dfn-logical-table-row">logical table rows</a>. It is
    used in conjunction with a <a href="#dfn-subject-map">subject map</a>
    to generate <a href="#dfn-rdf-triple">RDF triples</a> in a
    <a href="#dfn-triples-map">triples map</a>.</p>

    <p>A <a href="#dfn-predicate-object-map">predicate-object map</a>
    is represented by a resource that references the following
    other resources:</p>

    <ul>
    <li>Exactly one <a href="#dfn-predicate-map">predicate map</a>. It may be
    specified in two ways:
      <ol>
      <li>using the <code>rr:predicateMap</code> property, whose value
      <em class="rfc2119">MUST</em> be a
      <a href="#dfn-predicate-map">predicate map</a>, or</li>
      <li>using the <a href="#dfn-constant-shortcut-property">constant
      shortcut property</a> <code>rr:predicate</code>.</li>
      </ol>
    </li>
    <li>Exactly one <a href="#dfn-object-map">object map</a>. It may be
    specified in one of two ways:
      <ol>
      <li>using the <code>rr:objectMap</code> property, whose value
      <em class="rfc2119">MUST</em> be either an
      <a href="#dfn-object-map">object map</a>, or a
      <a href="#dfn-referencing-object-map">referencing object map</a>.</li>
      <li>using the <a href="#dfn-constant-shortcut-property">constant
      shortcut property</a> <code>rr:object</code>.</li>
      </ol>
    </li>
    </ul>

    <p>A <dfn id="dfn-predicate-map">predicate map</dfn> is a
    <a href="#dfn-term-map">term map</a>.</p>

    <p>An <dfn id="dfn-object-map">object map</dfn>
    is a <a href="#dfn-term-map">term map</a>.</p>


    <h2 id="term-map">7 Creating RDF Terms with Term Maps</h2>

    <div class="figure">
     <img src="images/term-map.png" alt="Diagram: The properties of term maps"/>
      <br /><br />
      Figure 4: The properties of term maps
    </div>

    <p>An <dfn id="dfn-rdf-term">RDF term</dfn> is either an
    <a href="#dfn-iri">IRI</a>, or a <a href="#dfn-blank-node">blank node</a>,
    or a <a href="#dfn-literal">literal</a>.</p>

    <p>A <dfn id="dfn-term-map">term map</dfn> is a function that generates
    an <a href="#dfn-rdf-term">RDF term</a> from a
    <a href="#dfn-logical-table-row">logical table row</a>. The result of
    that function is known as the term map's
    <a href="#dfn-generated-rdf-terms">generated RDF term</a>.</p>

    <p>Term maps
    are used to generate the subjects, predicates and objects of the
    <a href="#dfn-rdf-triple">RDF triples</a> that are generated by
    a <a href="#dfn-triples-map">triples map</a>. Consequently, there
    are several kinds of <a href="#dfn-term-map">term maps</a>,
    depending on where in the mapping they occur:
    <a href="#dfn-subject-map">subject maps</a>,
    <a href="#dfn-predicate-map">predicate maps</a>,
    <a href="#dfn-object-map">object maps</a> and
    <a href="#dfn-graph-map">graph maps</a>.</p>

    <p>A <a href="#dfn-term-map">term map</a> <em class="rfc2119">MUST</em>
    be exactly one of the following:</p>

    <ul>
    <li>a <a href="#dfn-constant-valued-term-map">constant-valued term map</a>,</li>
    <li>a <a href="#dfn-column-valued-term-map">column-valued term map</a>,</li>
    <li>a <a href="#dfn-template-valued-term-map">template-valued term map</a>.</li>
    </ul>

    <p>The <dfn id="dfn-referenced-columns">referenced columns</dfn> of a
    <a href="#dfn-term-map">term map</a> are the set of
    <a href="#dfn-column-name">column names</a> referenced
    in the term map and depend on the type of term map.</p>


    <h3 id="constant">7.1 Constant RDF Terms (<code>rr:constant</code>)</h3>

    <p>A <dfn id="dfn-constant-valued-term-map">constant-valued term map</dfn>
    is a <a href="#dfn-term-map">term map</a> that ignores the
    <a href="#dfn-logical-table-row">logical table row</a> and always generates
    the same RDF term. A constant-valued term map is represented by a
    resource that has exactly one <code>rr:constant</code>
    property.</p>

    <p>The <dfn id="dfn-constant-value">constant value</dfn> of a
    <a href="#dfn-constant-valued-term-map">constant-valued term map</a>
    is the RDF term that is the value of its <code>rr:constant</code>
    property.</p>

    <p>If the 
    <a href="#dfn-constant-valued-term-map">constant-valued term map</a>
    is a <a href="#dfn-subject-map">subject map</a>,
    <a href="#dfn-predicate-map">predicate map</a> or
    <a href="#dfn-graph-map">graph map</a>, then its
    <a href="#dfn-constant-value">constant value</a>
    <em class="rfc2119">MUST</em> be an <a href="#dfn-iri">IRI</a>.</p>

    <p>If the 
    <a href="#dfn-constant-valued-term-map">constant-valued term map</a>
    is an <a href="#dfn-object-map">object map</a>, then its
    <a href="#dfn-constant-value">constant value</a>
    <em class="rfc2119">MUST</em> be an
    <a href="#dfn-iri">IRI</a> or <a href="#dfn-literal">literal</a>.</p>

    <p>The <a href="#dfn-referenced-columns">referenced columns</a> of
    a <a href="#dfn-constant-valued-term-map">constant-valued term map</a>
    is the empty set.</p>

    <p>Constant-valued term maps can be expressed more concisely using the
    <dfn id="dfn-constant-shortcut-property">constant shortcut properties</dfn>
    <code>rr:subject</code>, <code>rr:predicate</code>,
    <code>rr:object</code> and <code>rr:graph</code>.
    Occurrances of these properties <em class="rfc2119">MUST</em> be 
    treated exactly as if the following triples were present in the
    mapping graph instead:</p>

    <table rules="all" summary="Constant shortcut properties and their replacements">
      <tr>
        <th>Triple involving constant shortcut property</th>
        <th>Replacement triples</th>
      </tr>
      <tr>
        <td><code><em>aaa</em> rr:subject <em>bbb</em>.</code></td>
        <td><code><em>aaa</em> rr:subjectMap [ rr:constant <em>bbb</em> ].</code></td>
      </tr>
      <tr>
        <td><code><em>aaa</em> rr:predicate <em>bbb</em>.</code></td>
        <td><code><em>aaa</em> rr:predicateMap [ rr:constant <em>bbb</em> ].</code></td>
      </tr>
      <tr>
        <td><code><em>aaa</em> rr:object <em>bbb</em>.</code></td>
        <td><code><em>aaa</em> rr:objectMap [ rr:constant <em>bbb</em> ].</code></td>
      </tr>
      <tr>
        <td><code><em>aaa</em> rr:graph <em>bbb</em>.</code></td>
        <td><code><em>aaa</em> rr:graphMap [ rr:constant <em>bbb</em> ].</code></td>
      </tr>
    </table>

    <p>The following example shows a
    <a href="#dfn-predicate-object-map">predicate-object map</a> that
    uses a constant-valued term map both for its predicate and for its
    object.</p>
    <pre class="ex-mapping">
[] rr:predicateMap [ rr:constant rdf:type ];
   rr:objectMap [ rr:constant ex:Employee ].</pre>
    
    <p>If added to a <a href="#dfn-triples-map">triples map</a>,
    this predicate-object map would add the following triple to
    all resources <code>?x</code> generated by the triples map:</p>
    <pre class="ex-output">
?x rdf:type ex:Employee.</pre>

    <p>The following example uses
    <a href="#dfn-constant-shortcut-property">constant shortcut properties</a>
    and is equivalent to the example above:</p>

    <pre class="ex-mapping">
[] rr:predicate rdf:type;
   rr:object ex:Employee.</pre>


    <h3 id="from-column">7.2 From a Column (<code>rr:column</code>)</h3>

    <p>A <dfn id="dfn-column-valued-term-map">column-valued term map</dfn>
    is a <a href="#dfn-term-map">term map</a> that is represented by
    a resource that has exactly one <code>rr:column</code> property.</p>

    <p>The value of the <code>rr:column</code> property
    <em class="rfc2119">MUST</em> be a valid
    <a href="#dfn-column-name">column name</a>. The
    <dfn id="dfn-column-value">column value</dfn> of the term map
    is the data value of that column in a given
    <a href="#dfn-logical-table-row">logical table row</a>.</p>

    <p>The <a href="#dfn-referenced-columns">referenced columns</a> of
    a <a href="#dfn-column-valued-term-map">column-valued term map</a>
    is the singleton set containing the value of <code>rr:column</code>.</p>

    <p>The following example defines an <a href="#dfn-object-map">object map</a>
    that generates <a href="#dfn-literal">literals</a> from the
    <code>DNAME</code> column of some logical table.</p>
    <pre class="ex-mapping">
[] rr:objectMap [ rr:column "DNAME" ].</pre>

    <p>Using the sample row from the
    <a href="#ex_DEPT"><code>DEPT</code> table</a> as a logical table
    row, the <a href="#dfn-column-value">column value</a> of the object map
    would be “<code>APPSERVER</code>”.</p>


    <h3 id="from-template">7.3 From a Template (<code>rr:template</code>)</h3>

    <p>A <dfn id="dfn-template-valued-term-map">template-valued term map</dfn>
    is a <a href="#dfn-term-map">term map</a> that is represented by
    a resource that has exactly one <code>rr:template</code> property.
    The value of the <code>rr:template</code> property
    <em class="rfc2119">MUST</em> be a valid
    <a href="#dfn-string-template">string template</a>.</p>

    <p>A <dfn id="dfn-string-template">string template</dfn> is a
    format string that can be used to build strings from multiple
    components. It can reference
    <a href="#dfn-column-name">column names</a> by enclosing
    them in curly braces. The following syntax rules apply to valid
    string templates:</p>

    <ul>
    <li>Pairs of unescaped curly braces <em class="rfc2119">MUST</em> enclose
    valid <a href="#dfn-column-name">column names</a>.</li>
    <li>Curly braces that do not enclose column names
    <em class="rfc2119">MUST</em> be escaped by a backslash character.
    This includes curly braces within column names.</li>
    <li>Backslash characters <em class="rfc2119">MUST</em> be escaped by
    doubling them with another backslash character. This includes
    backslashes within column names.</li>
    <li>If a template contains multiple pairs of unescaped curly braces,
    then adjacent pairs <em class="rfc2119">SHOULD</em> be separated by
    a character or string that does not occur anywhere in the data values
    of either column.</li>
    </ul>

    <p>The <dfn id="dfn-template-value">template value</dfn> of the term map
    for a given <a href="#dfn-logical-table-row">logical table row</a>
    is determined as follows:</p>

    <ol>
    <li>Let <code><em>result</em></code> be the
    <a href="#dfn-string-template">template string</a></li>
    <li>For each pair of unescaped curly braces in
    <code><em>result</em></code>:
      <ol>
      <li>Let <code><em>value</em></code> be the data value of the
      column whose name is enclosed in the curly braces</li>
      <li>If <code><em>value</em></code> is <code>NULL</code>,
      then return <code>NULL</code></li>
      <li>Apply <a href="#dfn-conversion-to-string">conversion to string</a>
      to <code><em>value</em></code></li>
      <li>If the <a href="#dfn-term-type">term type</a> is
      <code>rr:IRI</code>, then replace the pair of curly braces
      with an <a href="#dfn-iri-safe">IRI-safe</a> version of
      <code><em>value</em></code>; otherwise, replace the pair
      of curly braces with <code><em>value</em></code></li>
      </ol>
    </li>
    <li>Return <code><em>result</em></code></li>
    </ol>

    <p>The <dfn id="dfn-iri-safe">IRI-safe version</dfn> of a string
    is obtained by applying the following transformation to any character
    that is not in the
    <cite><a class="norm" href="http://tools.ietf.org/html/rfc3987#section-2.2">
    <code>iunreserved</code> production</a></cite> in
    [<cite><a href="#RFC3987">RFC3987</a></cite>]:</p>

    <ol>
    <li>Convert the character to a sequence of one or more octets
    using <cite><a class="norm" href="http://tools.ietf.org/html/rfc3629">UTF-8</a></cite>
    [<cite><a href="#RFC3629">RFC3629</a></cite>]</li>
    <li><cite><a class="norm" href="http://tools.ietf.org/html/rfc3986#section-2.1">Percent-encode</a></cite>
    each octet [<cite><a href="#RFC3986">RFC3986</a></cite>]</li>
    </ol>

    <p>The <a href="#dfn-referenced-columns">referenced columns</a> of
    a <a href="#dfn-template-valued-term-map">template-valued term map</a>
    is the set of <a href="#dfn-column-name">column names</a> enclosed
    in unescaped curly braces in the
    <a href="#dfn-string-template">template string</a>.</p>

    <p>The following example defines a
    <a href="#dfn-subject-map">subject map</a> that generates
    <a href="#dfn-iri">IRIs</a> from the
    <code>DEPTNO</code> column of a logical table.</p>
    <pre class="ex-mapping">
[] rr:subjectMap [ rr:template "http://data.example.com/department/{DEPTNO}" ].</pre>

    <p>Using the sample row from the
    <a href="#ex_DEPT"><code>DEPT</code> table</a> as a logical table
    row, the <a href="#dfn-template-value">template value</a> of the subject map
    would be:</p>

    <pre class="ex-output">http://data.example.com/department/10</pre>

    <p>The following example shows how an <a href="#dfn-iri-safe">IRI-safe</a>
    template value is created:</p>
    <pre class="ex-mapping">
[] rr:subjectMap [ rr:template "http://data.example.com/site/{LOC}" ].</pre>

    <p>Using the sample row from the
    <a href="#ex_DEPT"><code>DEPT</code> table</a> as a logical table
    row, the <a href="#dfn-template-value">template value</a> of the subject map
    would be:</p>

    <pre class="ex-output">http://data.example.com/site/NEW%20YORK</pre>

    <p>The space character is not in the <code>iunreserved</code> set,
    and therefore percent-encoding is applied to the character, yielding
    “<code>%20</code>”.</p>

    <p>The following example shows the use of backslash escapes in string
    templates. The template will generate a fancy title such as</p>
    <pre>{{{ Hello World! }}}</pre>
    <p>from a string “<code>Hello World!</code>” in the <code>TITLE</code> column.</p>
    <pre class="ex-mapping">
[] rr:objectMap [ rr:template "\\{\\{\\{ {TITLE} \\}\\}\\}" ].</pre>
    <p>Note that because <a class="norm" href=
    "http://www.w3.org/TeamSubmission/2008/SUBM-turtle-20080114/#sec-strings">
    backslashes need to be escaped by a second backslash
    in the Turtle syntax</a>
    [<cite><a href="#TURTLE">TURTLE</a></cite>],
    a double backslash is needed to escape each curly brace.</p>


    <h3 id="termtype">7.4 IRIs, Literal, Blank Nodes (<code>rr:termType</code>)</h3>

    <p>The <dfn id="dfn-term-type">term type</dfn> of a
    <a href="#dfn-column-valued-term-map">column-valued term map</a> or
    <a href="#dfn-template-valued-term-map">template-valued term map</a>
    determines the kind of
    <a href="#dfn-generated-rdf-terms">generated RDF term</a>
    (<a href="#dfn-iri">IRIs</a>, <a href="#dfn-blank-node">blank nodes</a> or
    <a href="#dfn-literal">literals</a>).</p>

    <p>If the term map has an optional <code>rr:termType</code> property,
    then its <a href="#dfn-term-type">term type</a> 
    is the value of that property. The value <em class="rfc2119">MUST</em>
    be an IRI and <em class="rfc2119">MUST</em> be
    one of the following options:</p>

    <ul>
    <li>If the term map is a <a href="#dfn-subject-map">subject map</a>:
    <code>rr:IRI</code> or <code>rr:BlankNode</code></li>
    <li>If the term map is a <a href="#dfn-predicate-map">predicate map</a>:
    <code>rr:IRI</code></li>
    <li>If the term map is an <a href="#dfn-object-map">object map</a>:
    <code>rr:IRI</code>, <code>rr:BlankNode</code>, or <code>rr:Literal</code></li>
    <li>If the term map is a <a href="#dfn-graph-map">graph map</a>:
    <code>rr:IRI</code></li>
    </ul>

    <p>If the term map does not have a <code>rr:termType</code> property,
    then its <a href="#dfn-term-type">term type</a> is:</p>

    <ul>
    <li>If the term map is an <a href="#dfn-object-map">object map</a>
    and a <a href="#dfn-column-valued-term-map">column-based term map</a>:
    <code>rr:Literal</code></li>
    <li>Otherwise: <code>rr:IRI</code></li>
    </ul>

    <p class="note">Term maps with term type <code>rr:IRI</code>
    cause <a href="#dfn-data-error">data errors</a> if the value is not a
    valid <a href="#dfn-iri">IRI</a>
    (see <a href="#dfn-generated-rdf-terms">generated RDF term</a> for details).
    Data values from the input database may require percent-encoding before
    they can be used in IRIs.
    <a href="#dfn-template-valued-term-map">Template-valued term maps</a>
    are a convenient way of percent-encoding data values.</p>


    <h3 id="language-tags">7.5 Language Tags (<code>rr:language</code>)</h3>

    <p>A <a href="#dfn-term-map">term map</a> with a
    <a href="#dfn-term-type">term type</a> of <code>rr:Literal</code>
    <em class="rfc2119">MAY</em> have a
    <dfn id="dfn-specified-language-tag">specified language tag</dfn>.
    It is represented by the <code>rr:language</code> property on a term map.
    If present, its value <em class="rfc2119">MUST</em> be
    a valid <a href="#dfn-language-tag">language tag</a>.</p>

    <p>A specified language tag causes generated literals to be
    language-tagged plain literals. In the following example, plain
    literals with language tag “<code>en-us</code>” (U.S. English)
    will be generated for the data values in the <code>DNAME</code>
    column.</p>

    <pre class="ex-mapping">
[] rr:objectMap [ rr:column "DNAME"; rr:language "en-us" ].
</pre>


    <h3 id="typed-literals">7.6 Typed Literals (<code>rr:datatype</code>)</h3>

    <p>A <dfn id="dfn-typeable-term-map">typeable term map</dfn> is a
    <a href="#dfn-term-map">term map</a> with a
    <a href="#dfn-term-type">term type</a> of <code>rr:Literal</code>
    that does not have a
    <a href="#dfn-specified-language-tag">specified langauge tag</a>.</p>

    <p>Typeable term maps may generate
    <a href="#dfn-typed-literal">typed literals</a>. The datatype
    of these literals can be explicitly specified using
    <code>rr:datatype</code>, or
    <a href="#dfn-corresponding-rdf-datatype">automatically determined</a>
    based on the SQL datatype of the underlying logical table column.</p>

    <p>A <a href="#dfn-typeable-term-map">typeable term map</a>
    <em class="rfc2119">MAY</em> have a <code>rr:datatype</code> property.
    Its value <em class="rfc2119">MUST</em> be an <a href="#dfn-iri">IRI</a>.
    This IRI is the <dfn id="dfn-specified-datatype">specified datatype</dfn>
    of the term map.</p>

    <p>A term map <em class="rfc2119">MUST NOT</em> have more than one
    <code>rr:datatype</code> value.</p>

    <p>A term map that is not a
    <a href="#dfn-typeable-term-map">typeable term map</a>
    <em class="rfc2119">MUST NOT</em> have an <code>rr:datatype</code>
    property.</p>

    <p>A <a href="#dfn-typeable-term-map">typeable term map</a>
    has an <dfn id="dfn-implicit-datatype">implicit datatype</dfn>
    and an <dfn id="dfn-implicit-transform">implicit transform</dfn>.
    They are determined as follows:</p>

    <ul>
    <li>If the term map is a
    <a href="#dfn-column-valued-term-map">column-valued term map</a>,
    then the implicit datatype is the
    <a href="#dfn-corresponding-rdf-datatype">corresponding RDF datatype</a>
    of the respective column in
    the <a href="#dfn-logical-table-row">logical table row</a>, and
    the implicit transform is the <a href="#dfn-rdf-transformation">RDF
    transformation</a> of the column.</li>

    <li>Otherwise, the term map must be a 
    <a href="#dfn-template-valued-term-map">template-valued term map</a>
    and its implicit datatype is <code>empty</code>, and
    its implicit transform is the identity transform.</li>
    </ul>

    <p>A <dfn id="dfn-datatype-override">datatype override</dfn>
    is in effect on a <a href="#dfn-typeable-term-map">typeable term map</a>
    if it has a <a href="#dfn-specified-datatype">specified datatype</a>,
    and the specified datatype is different from its
    <a href="#dfn-implicit-datatype">implicit datatype</a>.</p>

    <p>See <a href="#dfn-generated-rdf-terms">generated RDF term</a>
    for further details.</p>

    <p class="note">R2RML does not allow generating
    <a href="#dfn-plain-literal">plain literals</a> without
    <a href="#dfn-language-tag">language tag</a> from non-string
    columns. One can use a derived column that uses a SQL
    <code>CAST</code> expression instead.</p>

    <p>The following example shows an <a href="#dfn-object-map">object map</a>
    that overrides the default datatype of the logical table with
    an explicitly specified <code>xsd:positiveInteger</code> type.
    Whatever is in the <code>EMPNO</code> column will be subjected
    to <a href="#dfn-conversion-to-string">conversion to string</a>,
    and turned into a literal of that type.</p>

    <pre class="ex-mapping">
[] rr:objectMap [ rr:column "EMPNO"; rr:datatype xsd:positiveInteger ].
</pre>


    <h3 id="inverse">7.7 Inverse Expressions (<code>rr:inverseExpression</code>)</h3>

    <p>An <dfn id="dfn-inverse-expression">inverse expression</dfn> is a
    <a href="#dfn-string-template">string template</a> associated with
    a <a href="#dfn-column-valued-term-map">column-valued term map</a> or
    <a href="#dfn-template-valued-term-map">template-value term map</a>.
    It is represented by the value of the <code>rr:inverseExpression</code>
    property. This property is <em class="rfc2119">OPTIONAL</em> and there
    <em class="rfc2119">MUST NOT</em> be more than one for a term map.</p>

    <p>Inverse expressions are useful for optimizing
    <a href="#dfn-term-map">term maps</a>
    that reference derived columns in
    <a href="#dfn-r2rml-view">R2RML views</a>.
    An inverse expression specifies an expression that
    allows “reversing” of a <a href="#dfn-generated-rdf-terms">generated RDF term</a>
    and the construction of a SQL query that efficiently retrieves the
    <a href="#dfn-logical-table-row">logical table row</a> from which the
    term was generated. In particular, it allows the use of indexes
    on the underlying relational tables.</p>

    <p>Every pair of unescaped curly braces in the inverse expression is a
    <dfn id="dfn-column-reference">column reference in an inverse expression</dfn>.
    The string between the braces <em class="rfc2119">MUST</em> be a valid
    <a href="#dfn-column-name">column name</a>.</p>

    <p>An <a href="#dfn-inverse-expression">inverse expression</a>
    <em class="rfc2119">MUST</em> satisfy the following condition:</p>

    <ul>
    <li>Let <em>t</em> be the <a href="#dfn-logical-table">logical table</a>
    associated with this <a href="#dfn-term-map">term map</a></li>
    <li>Every <a href="#dfn-column-reference">column reference</a> in the
    inverse expression <em class="rfc2119">MUST</em> be an existing column
    in <em>t</em></li>
    <li>Given a <a href="#dfn-logical-table-row">logical table row</a>
    <em>r</em> in <em>t</em>, let <em>instantiation(r)</em> be the result of
    replacing each <a href="#dfn-column-reference">column reference</a>
    <em>c</em> in the inverse expression with:
      <ul>
      <li>the <a href="#dfn-quoted-data-value">quoted and escaped data value</a>
      of column
      <em>c</em> in <em>r</em>, if <em>c</em> is a
      <a href="#dfn-referenced-columns">referenced column</a>
      in the <a href="#dfn-term-map">term map</a></li>
      <li>the <a href="#dfn-column-name">column name</a>
      of column <em>c</em>, otherwise</li>
      </ul>
    </li>

    <li>Given a <a href="#dfn-logical-table-row">logical table row</a>
    <em>r</em> in <em>t</em>, let <em>same-term(r)</em>
    be the set of logical table rows in <em>t</em> that are the
    result of executing the following SQL query over the
    <a href="#dfn-sql-connection">SQL connection</a>:

    <pre>SELECT * FROM (<em>{query}</em>) AS tmp WHERE <em>{expr}</em></pre>

    where <code><em>{query}</em></code> is the
    <a href="#dfn-effective-sql-query">effective SQL query</a>
    of <em>t</em>, and <code><em>{expr}</em></code> is
    <em>instantiation(r)</em></li>

    <li>For every <a href="#dfn-logical-table-row">logical table row</a>
    <em>r</em> in <em>t</em> whose
    <a href="#dfn-generated-rdf-terms">generated RDF term</a> <em>g</em>
    is not <code>NULL</code>, <em>same-term(r)</em>
    <em class="rfc2119">MUST</em> be exactly the set of logical table rows
    in <em>t</em> whose
    <a href="#dfn-generated-rdf-terms">generated RDF term</a> is
    also <em>g</em>.</li>
    </ul>

    <p>For example, for the <code>DEPTID</code> column in the
    <a href="#dfn-logical-table">logical table</a> used for
    mapping the <code>DEPT</code> table in
    <a href="#example-r2rml-view">this example mapping</a>,
    an inverse expression could be defined as follows:</p>

    <pre class="ex-mapping">
[] rr:column "DEPTID";
   rr:inverseExpression "{DEPTNO} = substr({DEPTID},length('Department')+1)";
</pre>

    <p>This facilitates the use of an existing index on the <code>DEPTNO</code>
    column of the <a href="#ex_DEPT">DEPT table</a>.</p>

    <p>A <dfn id="dfn-quoted-data-value">quoted and escaped data value</dfn>
    is a SQL literal that can be used in a SQL query, such as:</p>

    <ul>
    <li><code>27</code></li>
    <li><code>'foo'</code></li>
    <li><code>'foo''bar'</code></li>
    </ul>


    <h2 id="foreign-key">8 Foreign Key Relationships among Logical Tables (<code>rr:parentTriplesMap</code>, <code>rr:joinCondition</code>, <code>rr:child</code> and <code>rr:parent</code>)</h2>

    <div class="figure">
     <img src="images/ref-object-map.png" alt="Diagram: The properties of referencing object maps"/>
      <br /><br />
      Figure 5: The properties of referencing object maps
    </div>

    <p>A <dfn id="dfn-referencing-object-map">referencing object map</dfn>
    allows using the subjects of another
    <a href="#dfn-triples-map">triples map</a> as the objects generated
    by a <a href="#dfn-predicate-object-map">predicate-object map</a>.
    Since both triples maps may be based on different
    <a href="#dfn-logical-table">logical tables</a>, this may require
    a join between the logical tables. A referencing object map is represented
    by a resource that:</p>

    <ul>
    <li>has exactly one <code>rr:parentTriplesMap</code> property, whose value
    <em class="rfc2119">MUST</em> be a
    <a href="#dfn-triples-map">triples map</a>, known as the
    referencing object map's <dfn id="dfn-parent-triples-map">parent
    triples map</dfn>.</li>

    <li><em class="rfc2119">MAY</em> have one or more
    <code>rr:joinCondition</code> properties, whose values
    <em class="rfc2119">MUST</em> be
    <a href="#dfn-join-condition">join conditions</a>.</li>
    </ul>

    <p>A <dfn id="dfn-join-condition">join condition</dfn> is a resource that
    has exactly two properties:</p>

    <ul>
    <li><code>rr:child</code>, whose value is known as the join condition's
    <dfn id="dfn-child-column">child column</dfn> and
    <em class="rfc2119">MUST</em> be a
    <a href="#dfn-column-name">column name</a> that exists in the
    <a href="#dfn-logical-table">logical table</a> of the
    <a href="#dfn-triples-map">triples map</a> that contains the
    referencing object map</li>
    <li><code>rr:parent</code>, whose value is known as the join condition's
    <dfn id="dfn-parent-column">parent column</dfn> and
    <em class="rfc2119">MUST</em> be a
    <a href="#dfn-column-name">column name</a> that exists in the
    <a href="#dfn-logical-table">logical table</a> of the
    referencing object map's
    <a href="#dfn-parent-triples-map">parent triples map</a>.</li>
    </ul>

    <p>The <dfn id="dfn-child-query">child query</dfn> of a
    <a href="#dfn-referencing-object-map">referencing object map</a>
    is the <a href="#dfn-effective-sql-query">effective SQL query</a>
    of the <a href="#dfn-logical-table">logical table</a> containing
    the referencing object map.</p>

    <p>The <dfn id="dfn-parent-query">parent query</dfn> of a
    <a href="#dfn-referencing-object-map">referencing object map</a>
    is the <a href="#dfn-effective-sql-query">effective SQL query</a>
    of the <a href="#dfn-logical-table">logical table</a> of its
    <a href="#dfn-parent-triples-map">parent triples map</a>.</p>

    <p>If the <a href="#dfn-child-query">child query</a> and
    <a href="#dfn-parent-query">parent query</a> of a
    <a href="#dfn-referencing-object-map">referencing object map</a>
    are not identical, then the referencing object map
    <em class="rfc2119">MUST</em> have at least one
    <a href="#dfn-join-condition">join condition</a>.</p>

    <p>The <dfn id="dfn-joint-sql-query">joint SQL query</dfn> of a 
    <a href="#dfn-referencing-object-map">referencing object map</a>
    is:</p>

    <ul>
    <li>If the referencing object map has no
    <a href="#dfn-join-condition">join condition</a>:
    <pre>SELECT * FROM (<em>{child-query}</em>) AS tmp</pre></li>
    <li>If the referencing object map has at least one join condition:
    <pre>
SELECT * FROM (<em>{child-query}</em>) AS child,
              (<em>{parent-query}</em>) AS parent
        WHERE child.<em>{child-column1}</em>=parent.<em>{parent-column1}</em>
          AND child.<em>{child-column2}</em>=parent.<em>{parent-column2}</em>
          AND ...</pre>
    where <code><em>{child-query}</em></code> is the referencing object map's
    <a href="#dfn-child-query">child query</a>,
    <code><em>{parent-query}</em></code> is its
    <a href="#dfn-parent-query">parent query</a>,
    <code><em>{child-column1}</em></code> and
    <code><em>{parent-column1}</em></code> are the
    <a href="#dfn-child-column">child column</a> and 
    <a href="#dfn-parent-column">parent column</a> of its first
    <a href="#dfn-join-condition">join condition</a>, and so on.
    The order of the join conditions is chosen arbitrarily.</li>
    </ul>

    <p>The following example shows a referencing object map as
    part of a <a href="#dfn-predicate-object-map">predicate-object map</a>:</p>
    <pre class="ex-mapping" id="ex-mapping">
[] rr:predicateObjectMap [
    rr:predicate ex:department;
    rr:refObjectMap [
        rr:parentTriplesMap &lt;#TriplesMap2&gt;;
        rr:joinCondition [
            rr:child "DEPTNO";
            rr:parent "DEPTNO";
        ];
    ];
].</pre>
    <p>If the logical table of the surrounding
    triples map is <code>EMP</code>, and the logical table
    of <code>&lt;#TriplesMap2&gt;</code> is <code>DEPT</code>,
    this would result in a join between these two tables
    with the condition</p>
    <pre>EMP.DEPTNO = DEPT.DEPTNO</pre>
    <p>and the objects of the triples would be generated using
    the subject map of <code>&lt;#TriplesMap2&gt;</code>.</p>

    <p>Given the two <a href="#example-input-database">example
    tables</a>, and subject maps as defined in the
    <a href="#ex-mapping">example mapping</a>, this would
    result in a triple:</p>

    <pre class="ex-output">&lt;http://data.example.com/employee/7369&gt; ex:department &lt;http://data.example.com/department/10&gt;.</pre>


    <h2 id="named-graphs">9 Assigning Triples to Named Graphs</h2>

    <div class="figure">
     <img src="images/graph-map.png" alt="Diagram: The properties of graph maps"/>
      <br /><br />
      Figure 6: The properties of graph maps
    </div>

    <p>Each triple generated from an <a href="#dfn-r2rml-mapping">R2RML
    mapping</a> is placed into one or
    more graphs of the <a href="#dfn-output-dataset">output dataset</a>.
    Possible target graphs are the unnamed
    <a href="#dfn-default-graph">default graph</a>, and the
    <a href="#dfn-iri">IRI</a>-named <a href="#dfn-named-graph">named
    graphs</a>.</p>

    <p>Any <a href="#dfn-subject-map">subject map</a>
    or <a href="#dfn-predicate-object-map">predicate-object map</a> <em class="rfc2119">MAY</em>
    have one or more associated <dfn id="dfn-graph-map">graph maps</dfn>.
    They are specified in one of two ways:</p>

    <ol>
    <li>using the <code>rr:graphMap</code> property, whose value
    <em class="rfc2119">MUST</em> be a
    <a href="#dfn-graph-map">graph map</a>,</li>
    <li>using the <a href="#dfn-constant-shortcut-property">constant
    shortcut property</a> <code>rr:graph</code>.</li>
    </ol>

    <p>Graph maps are themselves <a href="#dfn-term-map">term maps</a>.
    When <a href="#dfn-generating-rdf-triples">RDF
    triples are generated</a>, the set of target graphs is determined by
    taking into account any graph maps associated with the subject map
    or predicate-object map.</p>
    <p>If a <a href="#dfn-graph-map">graph map</a> generates the special
    IRI <code>rr:defaultGraph</code>, then the target graph is the
    <a href="#dfn-default-graph">default graph</a> of the
    <a href="#dfn-output-dataset">output dataset</a>.</p>

    <p>In the following <a href="#dfn-subject-map">subject map</a> example,
    all generated RDF triples will be stored in the named graph
    <code>ex:DepartmentGraph</code>.</p>
    <pre class="ex-mapping">
[] rr:subjectMap [
    rr:template "http://data.example.com/department/{DEPTNO}";
    rr:graphMap [ rr:graph ex:DepartmentGraph ];
].</pre>

    <p>This is equivalent to the following example, which uses a
    <a href="#dfn-constant-shortcut-property">constant shortcut property</a>:</p>

    <pre class="ex-mapping">
[] rr:subjectMap [
    rr:template "http://data.example.com/department/{DEPTNO}";
    rr:graph ex:DepartmentGraph;
].</pre>

    <p>In the following example, RDF triples are placed into named graphs
    according to the job title of employees:</p>

    <pre class="ex-mapping">
[] rr:subjectMap [
    rr:template "http://data.example.com/employee/{EMPNO}";
    rr:graphMap [ rr:template "http://data.example.com/jobgraph/{JOB}" ];
].</pre>

    <p>The triples generated from the <a href="#ex_EMP"><code>EMP</code>
    table</a> would be placed in the named graph with the following IRI:</p>

    <pre class="ex-output">
&lt;http://data.example.com/jobgraph/CLERK&gt;</pre>


    <h3 id="blank-nodes">9.1 Scope of Blank Nodes</h3>

    <p><a href="#dfn-blank-node">Blank nodes</a> in the
    <a href="#dfn-output-dataset">output dataset</a> are
    scoped to a single <a href="#dfn-rdf-graph">RDF graph</a>.
    If the same <a href="#dfn-blank-node-identifier">blank node identifier</a>
    occurs in multiple <a href="#dfn-rdf-triple">RDF triples</a>
    that are in the same graph, then the triples will share the
    same single blank node.
    If, however, the same blank node identifier occurs in multiple graphs,
    then a distinct blank node is created for each graph. An R2RML-generated
    blank node can never be shared by two triples in two different graphs.</p>

    <p>This implies that triples generated from a single logical table row
    will have different subjects if the subjects are blank nodes and the
    triples are placed into different graphs.</p>


    <h2 id="datatype-conversions">10 Datatype Conversions</h2>

    <p>This section defines various conversion rules applicable
    to data values. The rules are invoked in various places
    throughout this specification, in particular around
    <a href="#typed-literals"><code>rr:datatype</code></a>
    and in hte <a href="#dfn-term-generation-rules">term generation rules</a>.</p>

    <p>A <a href="#dfn-typed-literal">typed literal</a> of a
    <a href="#dfn-supported-rdf-datatype">supported RDF datatype</a> is
    <dfn id="dfn-ill-typed">ill-typed</dfn> if its
    <a href="#dfn-lexical-form">lexical form</a> is not in the
    <a href="#dfn-lexical-space">lexical space</a> of the RDF datatype
    identified by its <a href="#dfn-datatype-iri">datatype IRI</a>.</p>

    <p>For example, <code>"X"^^xsd:boolean</code> is ill-typed because
    “<code>X</code>” is not in the
    <a href="http://www.w3.org/TR/xmlschema-2/#boolean">lexical space of
    <code>xsd:boolean</code></a>
    [<cite><a href="#XMLSCHEMA2">XMLSCHEMA2</a></cite>].</p>


    <h3 id="datatype-table">10.1 Table of Corresponding Datatypes</h3>

    <p>The <dfn id="dfn-corresponding-rdf-datatype">corresponding RDF
    datatype</dfn> of a SQL datatype is given in the table below, or
    <code>empty</code> if the SQL datatype does not occur in the table.</p>

    <p>The <dfn id="dfn-rdf-transformation">RDF transformation</dfn> of a
    SQL datatype is a transformation rule given in the table below, or
    <em><a href="#dfn-conversion-to-string">conversion to string</a></em>
    if the SQL datatype does not occur in the table.</p>

    <p>The <dfn id="dfn-supported-rdf-datatype">supported RDF datatypes</dfn>
    are the datatypes for which an implementation can detect
    <a href="#dfn-ill-typed">ill-typed</a> literals. This set
    <em class="rfc2119">MUST</em> include all datatypes mentioned
    in the table below in the column “Corresponding RDF datatype”,
    according to their definitions in
    [<cite><a href="#XMLSCHEMA2">XMLSCHEMA2</a></cite>].
    This set <em class="rfc2119">MAY</em> include arbitrary further
    datatypes.</p>

    <table rules="all" summary="The RDF datatypes and transformations corresponding to SQL datatypes">
    <tr>
      <th>SQL datatype</th>
      <th>Corresponding RDF datatype</th>
      <th>Transformation</th>
    </tr>
    <tr>
      <td><code>BINARY</code>, <code>BINARY VARYING</code>, <code>BINARY LARGE OBJECT</code></td>
      <td><code>xsd:base64Binary</code></td>
      <td><a href="#dfn-base64-encoding">base64 encoding</a></td>
    </tr>
    <tr>
      <td><code>NUMERIC</code>, <code>DECIMAL</code></td>
      <td><code>xsd:decimal</code></td>
      <td><a href="#dfn-conversion-to-string">conversion to string</a></td>
    </tr>
    <tr>
      <td><code>SMALLINT</code>, <code>INTEGER</code>, <code>BIGINT</code></td>
      <td><code>xsd:integer</code></td>
      <td><a href="#dfn-conversion-to-string">conversion to string</a></td>
    </tr>
    <tr>
      <td><code>FLOAT</code>, <code>REAL</code>, <code>DOUBLE PRECISION</code></td>
      <td><code>xsd:double</code></td>
      <td><a href="#dfn-conversion-to-string">conversion to string</a></td>
    </tr>
    <tr>
      <td><code>BOOLEAN</code></td>
      <td><code>xsd:boolean</code></td>
      <td><a href="#dfn-conversion-to-boolean">conversion to boolean</a></td>
    </tr>
    <tr>
      <td><code>DATE</code></td>
      <td><code>xsd:date</code></td>
      <td><a href="#dfn-conversion-to-datetime">conversion to datetime</a></td>
    </tr>
    <tr>
      <td><code>TIME</code></td>
      <td><code>xsd:time</code></td>
      <td><a href="#dfn-conversion-to-datetime">conversion to datetime</a></td>
    </tr>
    <tr>
      <td><code>TIMESTAMP</code></td>
      <td><code>xsd:dateTime</code></td>
      <td><a href="#dfn-conversion-to-datetime">conversion to datetime</a></td>
    </tr>
    <tr>
      <td><code>INTERVAL</code></td>
      <td>undefined</td>
      <td>undefined</td>
    </tr>
    </table>

    <div class="note">
    <p>Any types not appearing in the table, including all character
    string types and vendor-specific types, will default to producing RDF
    <a href="#dfn-plain-literal">plain literals</a> by using
    <a href="#dfn-conversion-to-string">conversion to string</a>.</p>

    <p><a href="#dfn-r2rml-processor">R2RML processor</a> implementations
    are expected to augment the table with additional rows for mapping
    vendor-specific datatypes to appropriate XSD types.</p>
    </div>

    <p class="note">The translation of <code>INTERVAL</code> is left
    undefined due to the complexity of the translation.
    [<cite><a href="#SQL14">SQL14</a></cite>] describes a translation of
    <code>INTERVAL</code> to <code>xdt:yearMonthDuration</code> and
    <code>xdt:dayTimeDuration</code>.</p>

    <p id="datatype-examples">The following table shows examples
    of various SQL data values after
    <a href="#dfn-conversion-to-string">conversion to string</a>, and a
    <a href="#dfn-typed-literal">typed literal</a> of the
    <a href="#dfn-corresponding-rdf-datatype">corresponding RDF datatype</a>,
    derived by applying the SQL datatype's
    <a href="#dfn-rdf-transformation">RDF transformation</a>:</p>

    <table rules="all" summary="Examples of SQL data values converted to string and to typed literals">
    <tr>
      <th>SQL datatype</th>
      <th>Conversion to string example</th>
      <th>Typed literal example</th>
    </tr>
    <tr>
      <td><code>DECIMAL</code></td>
      <td><code>2000000000005.9</code></td>
      <td><code>"2000000000005.9"^^xsd:decimal</code></td>
    </tr>
    <tr>
      <td><code>DECIMAL</code></td>
      <td><code>2000000000000</code></td>
      <td><code>"2000000000000"^^xsd:decimal</code></td>
    </tr>
    <tr>
      <td><code>INTEGER</code></td>
      <td><code>-1</code></td>
      <td><code>"-1"^^xsd:integer</code></td>
    </tr>
    <tr>
      <td><code>REAL</code></td>
      <td><code>5.0E-1</code></td>
      <td><code>"5.0E-1"^^xsd:double</code></td>
    </tr>
    <tr>
      <td><code>REAL</code></td>
      <td><code>0E0</code></td>
      <td><code>"0E0"^^xsd:double</code></td>
    </tr>
    <tr>
      <td><code>DATE</code></td>
      <td><code>DATE 2011-08-23</code></td>
      <td><code>"2011-08-23"^^xsd:date</code></td>
    </tr>
    <tr>
      <td><code>TIME</code></td>
      <td><code>TIME 22:17:00</code></td>
      <td><code>"22:17:00"^^xsd:time</code></td>
    </tr>
    <tr>
      <td><code>TIME</code></td>
      <td><code>TIME 22:17:00.0000</code></td>
      <td><code>"22:17:00.0000"^^xsd:time</code></td>
    </tr>
    <tr>
      <td><code>TIME</code></td>
      <td><code>TIME 22:17:00+01:00</code></td>
      <td><code>"22:17:00+01:00"^^xsd:time</code></td>
    </tr>
    <tr>
      <td><code>TIMESTAMP</code></td>
      <td><code>TIMESTAMP 2011-08-23 22:17:00</code></td>
      <td><code>"2011-08-23T22:17:00"^^xsd:dateTime</code></td>
    </tr>
    </table>


    <h3 id="to-string">10.2 Conversion to string</h3>

    <p><dfn id="dfn-conversion-to-string">Conversion to string</dfn> is the process
    of transforming a SQL data value to a Unicode string. Its result
    <em class="rfc2119">MUST</em> be the same as evaluating the following
    SQL expression, as defined in [<cite><a href="#SQL2">SQL2</a></cite>]:</p>

    <pre>CAST(<em>value</em> AS CHARACTER VARYING(<em>max</em>))</pre>

    <p>where <code><em>value</em></code> is the
    <a href="#dfn-quoted-data-value">quoted and escaped form</a> of the
    SQL data value, and <code><em>max</em></code> is the
    implementation-dependent maximum length of a
    variable-length character string.</p>

    <div class="note">
    <p>An informative summary of the rules for casting standard SQL 2008
    datatypes to string follows. The right column of the table contains a
    <a href="http://www.w3.org/TR/xmlschema-2/#regexs">regular expression</a>
    that is matched by the string-converted form of all SQL data values of
    the types in the left column:</p>

    <table rules="all" summary="">
    <tr><th>Type</th><th>Pattern</th></tr>
    <tr><td><code>DECIMAL</code>, <code>NUMERIC</code></td><td><code>-?(\.\d+|\d+(\.\d+)?)</code></td></tr>
    <tr><td><code>SMALLINT</code>, <code>INTEGER</code>, <code>BIGINT</code></td><td><code>-?\d+</code></td></tr>
    <tr><td><code>FLOAT</code>, <code>REAL</code>, <code>DOUBLE PRECISION</code></td><td><code>0E0|-?[1-9]\.\d+</code></td></tr>
    <tr><td><code>DATE</code></td><td><code>\d\d\d\d-\d\d-\d\d</code></td></tr>
    <tr><td><code>TIME</code></td><td><code>\d\d:\d\d:\d\d(.\d+)?([+-]\d\d:\d\d)?</code></td></tr>
    <tr><td><code>TIMESTAMP</code></td><td><code>\d\d\d\d-\d\d-\d\d \d\d:\d\d:\d\d(.\d+)?([+-]\d\d:\d\d)?</code></td></tr>
    <tr><td><code>BOOLEAN</code></td><td><code>TRUE|FALSE</code></td></tr>
    </table>

    <p>The result of conversion to string is always the shortest possible
    string that, if interpreted as a SQL literal of the original SQL datatype,
    has the same value as the original SQL data value. For example,
    converting the <code>DECIMAL</code> value 1 to string yields <code>1</code>,
    not the longer equal-valued strings <code>01</code> or <code>1.0</code>.</p>
    </div>


    <h3 id="to-boolean">10.3 Conversion to <code>xsd:boolean</code></h3>

    <p><dfn id="dfn-conversion-to-boolean">Conversion to boolean</dfn>
    is the process of transforming a SQL data value of datatype
    <code>BOOLEAN</code> to a string that is compatible with the
    <code>xsd:boolean</code> datatype. It consists of the following
    steps:</p>

    <ol>
    <li>Apply <a href="#dfn-conversion-to-string">conversion to string</a>
    to the SQL data value,</li>
    <li>convert the resulting string to lowercase.</li>
    </ol>

    <p>Example: The result of converting a <code>BOOLEAN</code>
    SQL data value to string is either <code>TRUE</code> or <code>FALSE</code>.
    The resulting typed literal is either <code>"true"^^xsd:boolean</code> or
    <code>"false"^^xsd:boolean</code>.</p>


    <h3 id="datetime">10.4 Conversion to Datetime</h3>

    <p><dfn id="dfn-conversion-to-datetime">Conversion to datetime</dfn>
    is the process of transforming a SQL data value of datatype
    <code>DATE</code>, <code>TIME</code> or <code>TIMESTAMP</code>
    to a string that is compatible with the corresponding XSD datatype.
    It consists of the following steps:</p>

    <ol>
    <li>Apply <a href="#dfn-conversion-to-string">conversion to string</a>
    to the SQL data value.</li>
    <li>Remove any initial string “<code>DATE</code>”,
    “<code>TIME</code>” or “<code>TIMESTAMP</code>” and any leading spaces
    from the resulting string.</li>
    <li>If the SQL data value is of datatype <code>TIMESTAMP</code>,
    then replace the 11th character of the string (a space) with an
    upper-case “<code>T</code>”.</li>
    </ol>

    <p>Any fractional seconds and/or time zone interval present after
    conversion to string is included in the resulting string.</p>

    <p><a href="#datatype-examples">Examples for conversion to datetime</a>
    can be found in the table above.</p>


    <h3 id="binary">10.5 Conversion to <code>xsd:base64Binary</code></h3>

    <p><dfn id="dfn-base64-encoding">Base64 encoding</dfn> is the process
    of transforming a binary SQL data value to a string that is compatible with
    the <code>xsd:base64Binary</code> datatype, by applying
    <a href="http://www.w3.org/TR/xmlschema-2/#base64Binary">base64
    encoding as restricted for <code>xsd:base64Binary</code></a>
    [<cite><a href="#XMLSCHEMA2">XMLSCHEMA2</a></cite>] on the binary
    value.</p>


    <h2 id="generated-rdf">11 The Output Dataset</h2>

    <p>The <dfn id="dfn-output-dataset">output dataset</dfn> of an
    R2RML mapping is an <a href="#dfn-rdf-dataset">RDF dataset</a>
    that contains the
    <a href="#dfn-generating-rdf-triples">generated RDF triples</a>
    for each of the <a href="#dfn-triples-map">triples maps</a> of
    the R2RML mapping. The output dataset <em class="rfc2119">MUST NOT</em>
    contain any other <a href="#dfn-rdf-triple">RDF triples</a> or
    <a href="#dfn-named-graph">named graphs</a> besides these.</p>

    <p>If a table or column is not explicitly referenced in a
    <a href="#dfn-triples-map">triples map</a>,
    then no <a href="#dfn-rdf-triple">RDF triples</a>
    will be generated for that table or column.</p>

    <p>Conforming <a href="#dfn-r2rml-processor">R2RML processors</a>
    <em class="rfc2119">MAY</em> rename
    <a href="#dfn-blank-node">blank nodes</a> when providing
    access to the <a href="#dfn-output-dataset">output dataset</a>.
    This means that client applications may see actual
    <a href="#dfn-blank-node-identifier">blank node identifiers</a>
    that differ from those produced by the
    <a href="#dfn-r2rml-mapping">R2RML mapping</a>. Client applications
    <em class="rfc2119">SHOULD NOT</em>
    rely on the specific text of the blank node identifier for any purpose.</p>

    <p class="note"><a href="#dfn-rdf-dataset">RDF datasets</a> may
    contain empty <a href="#dfn-named-graph">named graphs</a>.
    R2RML cannot generate such output datasets.</p>


    <h3 id="generated-triples">11.1 The Generated RDF Triples of a Triples Map</h3>

    <p>This subsection describes the process of
    <dfn id="dfn-generating-rdf-triples">generating RDF triples</dfn>
    from a <a href="#dfn-triples-map">triples map</a>. This process adds
    <a href="#dfn-rdf-triple">RDF triples</a> to the 
    <a href="#dfn-output-dataset">output dataset</a>. Each generated triple
    is placed into one or more particular graphs of the output dataset.</p>

    <p>The generated RDF triples are determined by the following algorithm.
    R2RML processors <em class="rfc2119">MAY</em> use other means than
    implementing this algorithm to compute the generated RDF triples,
    as long as the result is the same.</p>

    <ol>
    <li>Let <code><em>sm</em></code> be the
    <a href="#dfn-subject-map">subject map</a> of the triples map</li>
    <li>Let <code><em>rows</em></code> be the result of evaluating the
    <a href="#dfn-effective-sql-query">effective SQL query</a>
    of the <a href="#dfn-triples-map">triples map</a>'s
    <a href="#dfn-logical-table">logical table</a> using the
    <a href="#dfn-sql-connection">SQL connection</a></li>
    <li>Let <code><em>classes</em></code> be the
    <a href="#dfn-class-iri">class IRIs</a> of <code><em>sm</em></code></li>
    <li>Let <code><em>sgm</em></code> be the set of
    <a href="#dfn-graph-map">graph maps</a> of <code><em>sm</em></code></li>

    <li>For each <a href="#dfn-logical-table-row">logical table row</a>
    <code><em>row</em></code> in <code><em>rows</em></code>,
    apply the following steps:
      <ol>
      <li>Let <code><em>subject</em></code> be the
      <a href="#dfn-generated-rdf-terms">generated RDF term</a> that results
      from applying <code><em>sm</em></code> to
      <code><em>row</em></code></li>
      <li>Let <code><em>subject_graphs</em></code> be the union of
      the <a href="#dfn-generated-rdf-terms">generated RDF terms</a>
      that result from applying any term maps in <code><em>sgm</em></code>
      to <code><em>row</em></code></li>
      <li>If <code><em>classes</em></code> is not empty, then for each
      <a href="#dfn-iri">IRI</a> in <code><em>classes</em></code>,
      <a href="#dfn-adding-triples">add the following triples</a> to the
      output dataset:
        <p>
        <strong>Subject:</strong> <code><em>subject</em></code><br />
        <strong>Predicate:</strong> <code>rdf:type</code><br />
        <strong>Object:</strong> <code><em>classes</em></code><br />
        <strong>Target graphs:</strong> If <code><em>sgm</em></code> is empty:
          <code>rr:defaultgraph</code>;
          otherwise: <code><em>subject_graphs</em></code>
        </p>
      </li>
      <li>For each <a href="#dfn-predicate-object-map">predicate-object map</a>
      of the <a href="#dfn-triples-map">triples map</a>, apply the following
      steps:
        <ol>
        <li>If the predicate-object map has no
        <a href="#dfn-object-map">object map</a> (but a
        <a href="#dfn-referencing-object-map">referencing object map</a>), then
        skip these substeps for this predicate-object map</li>
        <li>Let <code><em>predicate</em></code> be the
        <a href="#dfn-generated-rdf-terms">generated RDF term</a> that results
        from applying the predicate-object map's
        <a href="#dfn-predicate-map">predicate map</a>
        to <code><em>row</em></code></li>
        <li>Let <code><em>object</em></code> be the
        <a href="#dfn-generated-rdf-terms">generated RDF term</a> that results
        from applying the predicate-object map's
        <a href="#dfn-object-map">object map</a>
        to <code><em>row</em></code></li>
        <li>Let <code><em>pogm</em></code> be the set of 
        <a href="#dfn-graph-map">graph maps</a> of the predicate-object map</li>
        <li>Let <code><em>predicate-object_graphs</em></code> be the union of
        the <a href="#dfn-generated-rdf-terms">generated RDF terms</a>
        that result from applying any <a href="#dfn-graph-map">graph maps</a> in <code><em>pogm</em></code>
        to <code><em>row</em></code></li>
        <li><a href="#dfn-adding-triples">Add the following triples</a>
        to the output dataset:
          <p>
          <strong>Subject:</strong> <code><em>subject</em></code><br />
          <strong>Predicate:</strong> <code><em>predicate</em></code><br />
          <strong>Object:</strong> <code><em>object</em></code><br />
          <strong>Target graphs:</strong> If <code><em>sgm</em></code> and
          <code><em>pogm</em></code> are empty: <code>rr:defaultGraph</code>;
          otherwise: union of <code><em>subject_graphs</em></code>
          and <code><em>predicate-object_graphs</em></code>
          </p>
        </li>
        </ol>
      </li>
      </ol>
    </li>
    <li>For each <a href="#dfn-predicate-object-map">predicate-object map</a>
    of the <a href="#dfn-triples-map">triples map</a>, apply the following
    steps:
      <ol>
      <li>If the predicate-object map has no
      <a href="#dfn-referencing-object-map">referencing object map</a> (but a
      normal <a href="#dfn-object-map">object map</a>), then
      skip these substeps for this predicate-object map</li>
      <li>Let <code><em>psm</em></code> be the
      <a href="#dfn-subject-map">subject map</a> of the
      <a href="#dfn-parent-triples-map">parent triples map</a> of the
      referencing object map</li>
      <li>Let <code><em>pogm</em></code> be the set of 
      <a href="#dfn-graph-map">graph maps</a> of the predicate-object map</li>
      <li>Let <code><em>rows</em></code> be the result of evaluating the
      <a href="#dfn-joint-sql-query">joint SQL query</a>
      of the referencing object map</li>
      <li>For each <code><em>row</em></code> in <code><em>rows</em></code>,
      apply the following steps:
        <ol>
        <li>Let <code><em>child_row</em></code> be the subset of
        <code><em>row</em></code> whose columns are present in
        the referencing object map's
        <a href="#dfn-child-query">child query</a></li>
        <li>Let <code><em>parent_row</em></code> be the subset of
        <code><em>row</em></code> whose columns are present in
        the referencing object map's
        <a href="#dfn-parent-query">parent query</a></li>
        <li>Let <code><em>subject</em></code> be the
        <a href="#dfn-generated-rdf-terms">generated RDF term</a> that results
        from applying <code><em>sm</em></code> to
        <code><em>child_row</em></code></li>
        <li>Let <code><em>predicate</em></code> be the
        <a href="#dfn-generated-rdf-terms">generated RDF term</a> that results
        from applying the predicate-object map's
        <a href="#dfn-predicate-map">predicate map</a>
        to <code><em>child_row</em></code></li>
        <li>Let <code><em>object</em></code> be the
        <a href="#dfn-generated-rdf-terms">generated RDF term</a> that results
        from applying <code><em>psm</em></code> to
        <code><em>parent_row</em></code></li>
        <li>Let <code><em>subject_graphs</em></code> be the union of the
        <a href="#dfn-generated-rdf-terms">generated RDF terms</a>
        that result from applying any
        <a href="#dfn-graph-map">graph maps</a> of <code><em>sgm</em></code>
        to <code><em>child_row</em></code></li>
        <li>Let <code><em>predicate-object_graphs</em></code> be the union of the
        <a href="#dfn-generated-rdf-terms">generated RDF terms</a>
        that result from applying any
        <a href="#dfn-graph-map">graph maps</a> in <code><em>pogm</em></code>
        to <code><em>child_row</em></code></li>
        <li><a href="#dfn-adding-triples">Add the following triples</a>
        to the output dataset:
          <p>
          <strong>Subject:</strong> <code><em>subject</em></code><br />
          <strong>Predicate:</strong> <code><em>predicate</em></code><br />
          <strong>Object:</strong> <code><em>object</em></code><br />
          <strong>Target graphs:</strong> If neither <code><em>sgm</em></code>
          nor <code><em>pogm</em></code> has any <a href="#dfn-graph-map">graph
          maps</a>: <code>rr:defaultGraph</code>; otherwise: union of
          <code><em>subject_graphs</em></code>
          and <code><em>predicate-object_graphs</em></code>
          </p>
        </li>
        </ol>
      </li>
      </ol>
    </li>
    </ol>

    <p>The process of <dfn id="dfn-adding-triples">adding triples
    to the output dataset</dfn> takes as its input:</p>

    <ul>
    <li><strong>Subjects</strong>, a set of zero or more
    <a href="#dfn-iri">IRIs</a> or
    <a href="#dfn-blank-node">blank nodes</a></li>
    <li><strong>Predicates</strong>, a set of zero or more
    <a href="#dfn-iri">IRIs</a></li>
    <li><strong>Objects</strong>, a set of zero or more
    <a href="#dfn-rdf-term">RDF terms</a></li>
    <li><strong>Target graphs</strong>, a set of zero or more
    <a href="#dfn-iri">IRIs</a></li>
    </ul>

    <p>For each possible combination &lt;<em>s</em>, <em>p</em>, <em>o</em>&gt;,
    where <em>s</em> is a member of <em>Subjects</em>, <em>p</em> a member
    of <em>Predicates</em> and <em>o</em> a member of <em>Objects</em>:</p>

    <ol>
    <li>Generate an <a href="#dfn-rdf-triple">RDF triple</a> &lt;<em>s</em>, <em>p</em>,
    <em>o</em>&gt;</li>
    <li>If the set of target graphs includes <code>rr:defaultGraph</code>,
    add the triple to the <a href="#dfn-default-graph">default graph</a>
    of the <a href="#dfn-output-dataset">output dataset</a>.</li>
    <li>For each <a href="#dfn-iri">IRI</a> in the set of target
    graphs that is not equal to <code>rr:defaultGraph</code>,
    add the triple to a <a href="#dfn-default-graph">named graph</a>
    of that name in the <a href="#dfn-output-dataset">output dataset</a>.
    If the output dataset does not contain a named graph with that IRI,
    create it first.</li>
    </ol>

    <p><a href="#dfn-rdf-graph">RDF graphs</a> cannot contain duplicate
    <a href="#dfn-rdf-triple">RDF triples</a>. Placing multiple equal
    triples into the same graph has the same effect as placing it into
    the graph only once.</p>


    <h3 id="generated-rdf-terms">11.2 The Generated RDF Terms of a Term Map</h3>

    <p>A <a href="#dfn-term-map">term map</a> is a function that generates
    a set of <a href="#dfn-rdf-term">RDF terms</a> from a
    <a href="#dfn-logical-table-row">logical table row</a>. The result of that
    function can be:</p>

    <ul>
      <li>The empty set – if the term map references a <code>NULL</code> value,</li>
      <li>A singleton set of one RDF term – the common case,</li>
      <li>A <a href="#dfn-data-error">data error</a>.</li>
    </ul>

    <p>The <dfn id="dfn-generated-rdf-terms">generated RDF terms</dfn> 
    of a term map for a given logical table row are determined as follows:</p>

    <ul>
    <li>If the term map is a
    <a href="#dfn-constant-valued-term-map">constant-valued term map</a>,
    then the generated RDF terms are a singleton set containing 
    the term map's <a href="#dfn-constant-value">constant value</a>.</li>

    <li>If the term map is a
    <a href="#dfn-column-valued-term-map">column-valued term map</a>, then
    the generated RDF terms are determined by applying the
    <a href="#dfn-term-generation-rules">term generation rules</a> to its
    <a href="#dfn-column-value">column value</a>.</li>

    <li>If the term map is a
    <a href="#dfn-template-valued-term-map">template-valued term map</a>, then
    the generated RDF terms are determined by applying the
    <a href="#dfn-term-generation-rules">term generation rules</a> to its
    <a href="#dfn-template-value">template value</a>.</li>
    </ul>

    <p>The <dfn id="dfn-term-generation-rules">term generation rules</dfn>
    are as follows:</p>

    <ol>
    <li>If the value is <code>NULL</code>, then no RDF term is generated.</li>
    <li>Otherwise, if the <a href="#dfn-term-map">term map</a>'s
    <a href="#dfn-term-type">term type</a> is <code>rr:IRI</code>:
      <ol>
      <li>Apply <a href="#dfn-conversion-to-string">conversion to string</a>
      to the value.</li>
      <li>If the value is a valid
      <cite><a href="http://tools.ietf.org/html/rfc3987#section-2.2">
      absolute IRI</a></cite> [<cite><a href="#RFC3987">RFC3987</a></cite>],
      then generate an <a href="#dfn-iri">IRI</a>.</li>
      <li>Otherwise, prepend the value with the
      <a href="#dfn-base-iri">base IRI</a>. If the result is a valid
      <cite><a href="http://tools.ietf.org/html/rfc3987#section-2.2">
      absolute IRI</a></cite> [<cite><a href="#RFC3987">RFC3987</a></cite>],
      then generate an <a href="#dfn-iri">IRI</a> from the result.</li>
      <li>Otherwise, raise a <a href="#dfn-data-error">data error</a>.</li>
      </ol>
    </li>
    <li>Otherwise, if the term type is <code>rr:BlankNode</code>:
      <ol>
      <li>Apply <a href="#dfn-conversion-to-string">conversion to string</a>
      to the value.</li>
      <li>Generate
      a <a href="#dfn-blank-node-identifier">blank node</a> whose
      <a href="#dfn-blank-node-identifier">blank node identifier</a>
      is the value.</li>
      </ol>
    </li>
    <li>Otherwise, if the term type is <code>rr:Literal</code>:
      <ol>
      <li>If the term map has a <a href="#dfn-specified-language-tag">specified
      language tag</a>, then apply
      <a href="#dfn-conversion-to-string">conversion to string</a>
      to the value, and generate a
      <a href="#dfn-plain-literal">plain literal</a> with that
      language tag.</li>
      <li>Otherwise, if a <a href="#dfn-datatype-override">datatype override</a>
      is in effect on the term map:
        <ol>
          <li>Apply <a href="#dfn-conversion-to-string">conversion to string</a>
          to the value.</li>
          <li>Generate a <a href="#dfn-typed-literal">typed literal</a> whose
          <a href="#dfn-datatype-iri">datatype IRI</a> is the
          <a href="#dfn-specified-datatype">specified datatype</a>.</li>
          <li>If the specified datatype is a
          <a href="#dfn-supported-rdf-datatype">supported RDF datatype</a>
          and the generated typed literal is
          <a href="#dfn-ill-typed">ill-typed</a>, then raise a
          <a href="#dfn-data-error">data error</a>.</li>
        </ol>
      </li>
      <li>Otherwise, if the term map's
      <a href="#dfn-implicit-datatype">implicit datatype</a> is
      <code>empty</code>, then apply
      <a href="#dfn-conversion-to-string">conversion to string</a>
      to the value, and generate a
      <a href="#dfn-plain-literal">plain literal</a> without
      language tag.</li>
      <li>Otherwise, apply the term map's
      <a href="#dfn-implicit-transform">implicit transform</a>
      to the value, and generate a
      <a href="#dfn-typed-literal">typed literal</a> whose
      <a href="#dfn-datatype-iri">datatype IRI</a> is the
      <a href="#dfn-implicit-datatype">implicit datatype</a>.</li>
      </ol>
    </li>
    </ol>

    <p class="note">The algorithm uses simple string concatenation for
    obtaining an absolute IRI from a relative IRI, rather than the more complex
    algorithm defined in RFC 3986. This ensures that the original database
    value can be reconstructed from the generated IRI.</p>


    <h2 id="terminology">A. RDF Terminology (Informative)</h2>

    <p>This section lists some terms normatively defined in other specifications.</p>

    <p>The following terms are defined in <cite><em><a class="norm" href=
    "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">RDF Concepts and Abstract
    Syntax</a></em></cite> [<cite><a href="#RDF">RDF</a></cite>] and used in R2RML:</p>

    <ul>
      <li><dfn id="dfn-rdf-graph"><a class="type rdfGraph" href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-rdf-graph">RDF
      graph</a></dfn></li>

      <li><dfn id="dfn-rdf-triple"><a href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-rdf-triple">RDF
      triple</a></dfn></li>

      <li><dfn id="dfn-iri"><a class="type IRI" href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#section-rdf-graph">IRI</a></dfn>
      (corresponds to the Concepts and Abstract Syntax term <em>RDF URI
      reference</em>)</li>

      <li><dfn id="dfn-literal"><a class="type literal" href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-literal">literal</a></dfn></li>

      <li><dfn id="dfn-plain-literal"><a class="type plainLiteral" href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-plain-literal">plain
      literal</a></dfn></li>

      <li><dfn id="dfn-typed-literal"><a class="type typedLiteral" href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-typed-literal">typed
      literal</a></dfn></li>

      <li><dfn id="dfn-language-tag"><a class="type langTag" href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-language-identifier">language
      tag</a></dfn></li>

      <li><dfn id="dfn-lexical-form"><a class="type lexicalForm" href=
      "http://www.w3.org/TR/rdf-concepts/#dfn-lexical-form">lexical form</a></dfn></li>

      <li><dfn id="dfn-datatype-iri"><a class="type datatypeIRI" href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-datatype-URI">datatype
      IRI</a></dfn> (corresponds to the Concepts and Abstract Syntax term <em>datatype
      URI</em>)</li>

      <li><dfn id="dfn-lexical-space"><a class="type lexicalSpace" href=
      "http://www.w3.org/TR/rdf-concepts/#dfn-lexical-space">lexical space</a></dfn></li>

      <li><dfn id="dfn-blank-node"><a class="type bNode" href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-blank-node">blank
      node</a></dfn></li>

      <li><dfn id="dfn-blank-node-identifier"><a href=
      "http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-blank-node-id">
      blank node identifier</a></dfn></li>
    </ul>

    <p>The following terms are defined in <cite><em><a class="norm" href=
    "http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/">SPARQL Query Language for
    RDF</a></em></cite> [<cite><a href="#SPARQL">SPARQL</a></cite>] and used in
    R2RML:</p>

    <ul>
      <li><dfn id="dfn-rdf-dataset"><a href=
      "http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/#rdfDataset">RDF
      dataset</a></dfn></li>

      <li><dfn id="dfn-default-graph"><a href=
      "http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/#rdfDataset">default
      graph</a></dfn></li>

      <li><dfn id="dfn-named-graph"><a href=
      "http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/#rdfDataset">named
      graph</a></dfn></li>
    </ul>


    <h2 id="index">B. Index of R2RML Vocabulary Terms (Informative)</h2>

    <p>This appendix lists all the classes, properties and other terms
    defined by this specification within the
    <a href="#dfn-r2rml-vocabulary">R2RML vocabulary</a>.</p>

    <p>An RDFS representation of the vocabulary is available from
    the <a href="http://www.w3.org/ns/r2rml#">namespace IRI</a>.</p>


    <h3 id="class-index">B.1 Classes</h3>

    <table class="term-index">
      <tr><th>Class</th><th>Represents</th></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#GraphMap"><code>rr:GraphMap</code></a></th>
      <td><a href="#dfn-graph-map">graph map</a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#Join"><code>rr:Join</code></a></th>
      <td><a href="#dfn-join-condition">join condition</a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#LogicalTable"><code>rr:LogicalTable</code></a></th>
      <td><a href="#dfn-logical-table">logical table</a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#ObjectMap"><code>rr:ObjectMap</code></a></th>
      <td><a href="#dfn-object-map">object map</a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#PredicateMap"><code>rr:PredicateMap</code></a></th>
      <td><a href="#dfn-predicate-map">predicate map</a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#PredicateObjectMap"><code>rr:PredicateObjectMap</code></a></th>
      <td><a href="#dfn-predicate-object-map">predicate-object map</a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#RefObjectMap"><code>rr:RefObjectMap</code></a></th>
      <td><a href="#dfn-referencing-object-map">referencing object map</a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#SubjectMap"><code>rr:SubjectMap</code></a></th>
      <td><a href="#dfn-subject-map">subject map</a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#TriplesMap"><code>rr:TriplesMap</code></a></th>
      <td><a href="#dfn-triples-map">triples map</a></td></tr>
    </table>

    <h3 id="property-index">B.2 Properties</h3>

    <p>The cardinality column indicates how often this property
    occurs within its context. Note that additional constraints
    not stated in this table might apply, and making a property
    forbidden or required in certain situations.</p>

    <table class="term-index">
      <tr><th>Property</th><th>Represents</th><th>Context</th><th>Cardinality</th></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#child"><code>rr:child</code></a></th>
        <td><a href="#dfn-child-column">child column</a></td>
        <td><a href="#dfn-join-condition">join condition</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#class"><code>rr:class</code></a></th>
        <td><a href="#dfn-class-iri">class IRI</a></td>
        <td><a href="#dfn-subject-map">subject map</a></td>
        <td>0…∞</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#column"><code>rr:column</code></a></th>
        <td><a href="#dfn-column-valued-term-map">column name</a></td>
        <td><a href="#dfn-column-valued-term-map">column-valued term map</a></td><td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#datatype"><code>rr:datatype</code></a></th>
        <td><a href="#dfn-specified-datatype">specified datatype</a></td>
        <td><a href="#dfn-term-map">term map</a></td>
        <td>0…1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#constant"><code>rr:constant</code></a></th>
        <td><a href="#dfn-constant-value">constant value</a></td>
        <td><a href="#dfn-constant-valued-term-map">constant-valued term map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#graph"><code>rr:graph</code></a></th>
        <td><a href="#dfn-constant-shortcut-property">constant shortcut property</a></td>
        <td><a href="#dfn-subject-map">subject map</a>, <a href="#dfn-predicate-object-map">predicate-object map</a></td>
        <td>0…∞</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#graphMap"><code>rr:graphMap</code></a></th>
        <td><a href="#dfn-graph-map">graph map</a></td>
        <td><a href="#dfn-subject-map">subject map</a>, <a href="#dfn-predicate-object-map">predicate-object map</a></td>
        <td>0…∞</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#inverseExpression"><code>rr:inverseExpression</code></a></th>
        <td><a href="#dfn-inverse-expression">inverse-expression</a></td>
        <td><a href="#dfn-term-map">term map</a></td>
        <td>0…1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#joinCondition"><code>rr:joinCondition</code></a></th>
        <td><a href="#dfn-join-condition">join condition</a></td>
        <td><a href="#dfn-referencing-object-map">referencing object map</a></td>
        <td>0…∞</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#language"><code>rr:language</code></a></th>
        <td><a href="#dfn-specified-language-tag">specified language tag</a></td>
        <td><a href="#dfn-term-map">term map</a></td>
        <td>0…1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#logicalTable"><code>rr:logicalTable</code></a></th>
        <td><a href="#dfn-triples-map">logical table</a></td>
        <td><a href="#dfn-triples-map">triples map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#object"><code>rr:object</code></a></th>
        <td><a href="#dfn-constant-shortcut-property">constant shortcut property</a></td>
        <td><a href="#dfn-predicate-object-map">predicate-object map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#objectMap"><code>rr:objectMap</code></a></th>
        <td><a href="#dfn-object-map">object map</a></td>
        <td><a href="#dfn-predicate-object-map">predicate-object map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#parent"><code>rr:parent</code></a></th>
        <td><a href="#dfn-parent-column">parent column</a></td>
        <td><a href="#dfn-join-condition">join condition</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#parentTriplesMap"><code>rr:parentTriplesMap</code></a></th>
        <td><a href="#dfn-parent-triples-map">parent triples map</a></td>
        <td><a href="#dfn-referencing-object-map">referencing object map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#predicate"><code>rr:predicate</code></a></th>
        <td><a href="#dfn-constant-shortcut-property">constant shortcut property</a></td>
        <td><a href="#dfn-predicate-object-map">predicate-object map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#predicateMap"><code>rr:predicateMap</code></a></th>
        <td><a href="#dfn-predicate-map">predicate map</a></td>
        <td><a href="#dfn-predicate-object-map">predicate-object map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#predicateObjectMap"><code>rr:predicateObjectMap</code></a></th>
        <td><a href="#dfn-triples-map">predicate-object map</a></td>
        <td><a href="#dfn-triples-map">triples map</a></td>
        <td>0…∞</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#sqlQuery"><code>rr:sqlQuery</code></a></th>
        <td><a href="#dfn-sql-query">SQL query</a></td>
        <td><a href="#dfn-r2rml-view">R2RML view</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#sqlVersion"><code>rr:sqlVersion</code></a></th>
        <td><a href="#dfn-sql-version-identifier">SQL version identifier</a></td>
        <td><a href="#dfn-r2rml-view">R2RML view</a></td>
        <td>0…∞</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#subject"><code>rr:subject</code></a></th>
        <td><a href="#dfn-constant-shortcut-property">constant shortcut property</a></td>
        <td><a href="#dfn-triples-map">triples map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#subjectMap"><code>rr:subjectMap</code></a></th>
        <td><a href="#dfn-triples-map">subject map</a></td>
        <td><a href="#dfn-triples-map">triples map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#tableName"><code>rr:tableName</code></a></th>
        <td><a href="#dfn-table-or-view-name">table or view name</a></td>
        <td><a href="#dfn-sql-base-table-or-view">SQL base table or view</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#template"><code>rr:template</code></a></th>
        <td><a href="#dfn-string-template">string template</a></td>
        <td><a href="#dfn-template-valued-term-map">template-valued term map</a></td>
        <td>1</td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#termType"><code>rr:termType</code></a></th>
        <td><a href="#dfn-term-type">term type</a></td>
        <td><a href="#dfn-term-map">term map</a></td>
        <td>0…1</td></tr>
    </table>


    <h3 id="other-index">B.3 Other Terms</h3>

    <table class="term-index">
      <tr><th>Term</th><th>Denotes</th><th>Used with property</th></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#defaultGraph"><code>rr:defaultGraph</code></a></th>
        <td><a href="#dfn-default-graph">default graph</a></td>
        <td><a href="#named-graphs"><code>rr:graph</code></a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#SQL2008"><code>rr:SQL2008</code></a></th>
        <td><a href="#conformance">Core SQL 2008</a></td>
        <td><a href="#dfn-sql-version-identifier"><code>rr:sqlVersion</code></a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#IRI"><code>rr:IRI</code></a></th>
        <td><a href="#dfn-iri">IRI</a></td>
        <td><a href="#dfn-term-type"><code>rr:termType</code></a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#BlankNode"><code>rr:BlankNode</code></a></th>
        <td><a href="#dfn-blank-node">blank node</a></td>
        <td><a href="#dfn-term-type"><code>rr:termType</code></a></td></tr>
      <tr><th><a href="http://www.w3.org/ns/r2rml#Literal"><code>rr:Literal</code></a></th>
        <td><a href="#dfn-literal">literal</a></td>
        <td><a href="#dfn-term-type"><code>rr:termType</code></a></td></tr>
    </table>


    <h2 id="references">C. References</h2>

    <h3 id="normative-refs">C.1 Normative References</h3>

    <dl>
      <dt><a id="RDF" name="RDF">[RDF]</a></dt>

      <dd><cite><a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">Resource
      Description Framework (RDF): Concepts and Abstract Syntax</a></cite>, Graham Klyne,
      Jermey J. Carroll, Editors. World Wide Web Consortium, 10 February 2004. This
      version is http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/. The latest version
      is http://www.w3.org/TR/rdf-concepts/.</dd>

      <dt><a id="RFC2119" name="RFC2119">[RFC2119]</a></dt>

      <dd><cite><a href="http://tools.ietf.org/html/rfc2119">Key words
      for use in RFCs to Indicate Requirement Levels</a></cite>, S. Bradner,
      March 1997.
      Internet RFC 2119, http://tools.ietf.org/html/rfc2119.</dd> 

      <dt><a id="RFC3629" name="RFC3629">[RFC3629]</a></dt>

      <dd><cite><a href="http://tools.ietf.org/html/rfc3629">UTF-8, a
      transformation format of ISO 10646</a></cite>, F. Yergeau. November 2003.
      Internet RFC 3629, http://tools.ietf.org/html/rfc3629.</dd> 

      <dt><a id="RFC3986" name="RFC3986">[RFC3986]</a></dt>

      <dd><cite><a href="http://tools.ietf.org/html/rfc3986">Uniform Resource
      Identifier (URI): Generic Syntax</a></cite>, T. Berners-Lee, R. Fielding,
      L. Masinter. January 2005.
      Internet RFC 3986, http://tools.ietf.org/html/rfc3986.</dd> 

      <dt><a id="RFC3987" name="RFC3987">[RFC3987]</a></dt>

      <dd><cite><a href="http://tools.ietf.org/html/rfc3987">Internationalized
      Resource Identifiers (IRIs)</a></cite>, M. Duerst, M. Suignard.  January 2005.
      Internet RFC 3987, http://tools.ietf.org/html/rfc3987.</dd> 

      <dt><a id="SPARQL" name="SPARQL">[SPARQL]</a></dt>

      <dd><cite><a href="http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/">SPARQL
      Query Language for RDF</a></cite>, Eric Prud'hommeaux, Andy Seaborne, Editors.
      World Wide Web Consortium, 15 January 2008. This version is
      http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/. The latest version is
      http://www.w3.org/TR/rdf-sparql-query/.</dd>

      <dt><a id="SQL1" name="SQL1">[SQL1]</a></dt>

      <dd><cite>ISO/IEC 9075-1:2008 SQL - Part 1: Framework (SQL/Framework)</cite>.
      International Organization for
      Standardization, 27 January 2009.</dd>

      <dt><a id="SQL2" name="SQL2">[SQL2]</a></dt>

      <dd><cite>ISO/IEC 9075-2:2008 SQL - Part 2: Foundation (SQL/Foundation)</cite>.
      International Organization for
      Standardization, 27 January 2009.</dd>

      <dt><a id="TURTLE" name="TURTLE">[TURTLE]</a></dt>

      <dd><cite><a href=
      "http://www.w3.org/TeamSubmission/2008/SUBM-turtle-20080114/">Turtle - Terse RDF
      Triple Language</a></cite>, Dave Beckett, Tim Berners-Lee. World Wide Web
      Consortium, 14 January 2008. This version is
      http://www.w3.org/TeamSubmission/2008/SUBM-turtle-20080114/. The latest version is
      http://www.w3.org/TeamSubmission/turtle/.</dd>

      <dt><a id="XMLSCHEMA2" name="XMLSCHEMA2">[XMLSCHEMA2]</a></dt>

      <dd><cite><a href="http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/">XML
      Schema Part 2: Datatypes Second Edition</a></cite>,
      Paul V. Biron, Ashok Malhotra. World Wide Web Consortium,
      28 October 2004. This version is
      http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/.
      The latest version is http://www.w3.org/TR/xmlschema-2/.</dd>
    </dl>


    <h3 id="non-normative-refs">C.2 Other References</h3>

    <dl>
      <dt><a id="DM" name="DM">[DM]</a></dt>

      <dd><cite><a href="http://www.w3.org/TR/2011/WD-rdb-direct-mapping-20110920/">A
      Direct Mapping of Relational Data to RDF</a></cite>, Alexandre Bertails, Marcelo Arenas,
      Eric Prud'hommeaux, Juan Sequeda, Editors. World Wide Web Consortium, 20 September 2011.
      This version is http://www.w3.org/TR/2011/WD-rdb-direct-mapping-20110920/. The latest
      version is http://www.w3.org/TR/rdb-direct-mapping/. This document is work in
      progress.</dd>

      <dt><a id="SQL14" name="SQL14">[SQL14]</a></dt>

      <dd><cite>ISO/IEC 9075-14:2008 SQL - Part 14: XML-Related Specifications (SQL/XML)</cite>.
      International Organization for Standardization, 27 January 2009.</dd>

      <dt><a id="SQLIRIS" name="SQLIRIS">[SQLIRIS]</a></dt>

      <dd><cite><a href="http://www.w3.org/2001/sw/rdb2rdf/wiki/SQL_Version_IRIs">SQL
      Version IRIs</a></cite>, Members of the W3C RDB2RDF Working Group.
      The latest version is http://www.w3.org/2001/sw/rdb2rdf/wiki/SQL_Version_IRIs.
      This is a public wiki page.</dd>

      <dt><a id="TC" name="TC">[TC]</a></dt>

      <dd><cite><a href="http://www.w3.org/2001/sw/rdb2rdf/test-cases/">R2RML and Direct Mapping Test Cases (Editor's Draft)</a></cite>, Boris Villaz&oacute;n-Terrazas, Michael Hausenblas, Alexander de Leon, Editors. World Wide Web Consortium, 31 August 2011. The latest version is http://www.w3.org/2001/sw/rdb2rdf/test-cases/. This document is work in progress.</dd>

      <dt><a id="UCNR" name="UCNR">[UCNR]</a></dt>

      <dd><cite><a href="http://www.w3.org/TR/2010/WD-rdb2rdf-ucr-20100608/">Use Cases
      and Requirements for Mapping Relational Databases to RDF</a></cite>, Eric
      Prud'hommeaux, Michael Hausenblas, Editors. World Wide Web Consortium, 8 June 2010.
      This version is http://www.w3.org/TR/2010/WD-rdb2rdf-ucr-20100608/. The latest
      version is http://www.w3.org/TR/rdb2rdf-ucr/. This document is work in
      progress.</dd>
    </dl>


    <h2 id="acknowledgements">D. Acknowledgements (Informative)</h2>

	<p>The Editors would like to give special thanks to the following members: Nuno Lopes for help in designing the datatyping related text, David McNeil for raising many of the issues that needed addressing, Eric Prud'hommeaux for designing the SQL compatibility text, and Boris Villaz&oacute;n-Terrazas for drawing all the diagrams.
	</p>
    <p>In addition, the Editors gratefully acknowledge contributions from: Marcelo Arenas, S&ouml;ren Auer, Samir Batla, Alexander de Leon, Orri Erling, Lee Feigenbaum, Enrico Franconi, Howard Greenblatt, Wolfgang Halb, Harry Halpin, Michael Hausenblas, Patrick Hayes, Ivan Herman, Nophadol Jekjantuk, Li Ma, Nan Ma, Ashok Malhotra, Ivan Mikhailov, Percy Enrique Rivera Salas, Juan Sequeda, Ben Szekely, Ted Thibodeau, and Edward Thomas.
    </p>
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