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"http://www.w3.org/Icons/w3c_home" /></a>
<h1 id="main">RDF Data Access Use Cases and Requirements</h1>
<h2 id="main_what">W3C Working Draft 25 March 2005</h2>
<!-- h2 id="main_what">Live Draft ( --><!-- fooey -->
<!-- $Revision: 1.2 $ of $Date: 2005/03/25 22:41:36 $)</h2 -->
<dl>
<dt>This Version:</dt>
<dd><a href="http://www.w3.org/TR/2005/WD-rdf-dawg-uc-20050325/">
http://www.w3.org/TR/2005/WD-rdf-dawg-uc-20050325/</a>
</dd>
<dt>Previous Version:</dt>
<dd><a href="http://www.w3.org/TR/2004/WD-rdf-dawg-uc-20041012/">http://www.w3.org/TR/2004/WD-rdf-dawg-uc-20041012/</a></dd>
<dt>Latest Version:</dt>
<dd><a href="http://www.w3.org/TR/rdf-dawg-uc/">
http://www.w3.org/TR/rdf-dawg-uc/</a>
</dd>
<dt>Editor:</dt>
<dd><a href="mailto:kendall@monkeyfist.com">Kendall Grant Clark</a>,
University of Maryland Information and Network Dynamics Laboratory</dd>
<!-- dt>published W3C Technical Report Version:</dt>
<dd><a href="http://www.w3.org/TR/2004/WD-rdf-dawg-uc-20041012/">12 Oct
2004</a>; see also <a href=
"http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/">public-rdf-dawg-comments@w3.org
Mail Archives</a></dd -->
</dl>
<p class="copyright"><a href=
"http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> ©
2004, 2005 <a href="http://www.w3.org/"><acronym title=
"World Wide Web Consortium">W3C</acronym></a><sup>®</sup> ( <a href=
"http://www.csail.mit.edu/"><acronym title=
"Massachusetts Institute of Technology">MIT</acronym></a>, <a href=
"http://www.ercim.org/"><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=
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and <a href=
"http://www.w3.org/Consortium/Legal/copyright-documents">document use</a>
rules apply.</p>
</div>
<hr title="Separator for header" />
<div>
<h2 id="abstract">Abstract</h2>
<p>This document specifies use cases, requirements, and objectives for an
<a href="http://www.w3.org/RDF/">RDF</a> query language and data access
protocol. It suggests how an RDF query language and data access protocol
could be used in the construction of novel, useful Semantic Web
applications in areas like web publishing, personal information
management, transportation, and tourism.</p>
</div>
<div>
<h2><a name="status" id="status">Status of This Document</a></h2>
<p>Since the October 2004 draft of this document, the <a
href="http://www.w3.org/2001/sw/DataAccess/">RDF Data Access Working Group</a> has</p>
<ul>
<li>adopted a WSDL requirement and
a sorting objective (see <a href="#changes">change log</a>
for details)</li>
<li>postponed some design issues to a future version due to lack
of implementation and design experience (<a
href="http://www.w3.org/2001/sw/DataAccess/issues#cascadedQueries"
>cascadedQueries</a>, <a
href="http://www.w3.org/2001/sw/DataAccess/issues#accessingCollections"
>accessingCollections</a>)</li>
<li>changed our approach to the <a href="#d4.1">Human-friendly Syntax</a> objective (see issue <a
href="http://www.w3.org/2001/sw/DataAccess/issues#punctuationSyntax"
>punctuationSyntax</a> and upcoming design document revisions)
</li>
</ul>
<p>We invite feedback on which features
are required for a first version of SPARQL and which should be
postponed in order to expedite deployment of others. Please send
comments to <a href="mailto:public-rdf-dawg-comments@w3.org"
>public-rdf-dawg-comments@w3.org</a>, a mailing list with a <a
href="http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/"
>public archive</a>.</p>
<p>This document has been produced by the <a
href="http://www.w3.org/2001/sw/DataAccess/">RDF Data Access
Working Group</a>, along with three design documents: <cite><a
href="http://www.w3.org/TR/rdf-sparql-query/">SPARQL Query
Language for RDF</a></cite>, <cite><a
href="http://www.w3.org/TR/rdf-sparql-protocol/">SPARQL Protocol
for RDF</a></cite>, and <cite><a
href="http://www.w3.org/TR/rdf-sparql-XMLres/">SPARQL Variable
Binding Results XML Format</a></cite>. This work is part of the
<a href="http://www.w3.org/2001/sw/">Semantic Web Activity</a> in
the W3C <a href="http://www.w3.org/TandS/">Technology &
Society Domain</a>.</p>
<!-- p><em>This is a live document and is edited frequently. Recent edits may
not have been reviewed by the RDF Data Access Working Group.</em> The
<a href="http://www.w3.org/2001/sw/DataAccess/">RDF Data Access Working
Group</a> has adopted some but not all of the requirements in this
document; the remaining requirements are still under discussion. We
invite feedback especially with respect to which use cases and
requirements should be elaborated, clarified, removed, or added.</p -->
<p class="bp"><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 class="bp">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 class="bp">This document was produced under the <a href=
"http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004
W3C Patent Policy</a>. The Working Group maintains a <a rel="disclosure"
href="http://www.w3.org/2001/sw/DataAccess/Disclosures">public list of
patent disclosures</a> relevant to this document; that page also includes
instructions for disclosing [and excluding] a patent. An individual who
has actual knowledge of a patent which the individual believes contains
Essential Claim(s) with respect to this specification should 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>
<p class="bp">Per <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Exclusion">section
4 of the W3C Patent Policy</a>, Working Group participants have 150
days from the title page date of this document to exclude essential
claims from the W3C RF licensing requirements with respect to this
document series. Exclusions are with respect to the exclusion
reference document, defined by the W3C Patent Policy to be the
latest version of a document in this series that is published no
later than 90 days after the title page date of this
document.</p>
</div>
<hr />
<h1 id="toc">Table of Contents</h1>
<ol>
<li><a href="#intro">Introduction</a></li>
<li>
<a href="#uc">Use Cases</a>
<ul>
<li>2.1 <a href="#u2.1">Finding an Email Address</a></li>
<li>2.2 <a href="#u2.2">Finding Information about Motorcycle
Parts</a></li>
<li>2.3 <a href="#u2.3">Finding Unknown Media Objects</a></li>
<li>2.4 <a href="#u2.4">Monitoring News Events</a></li>
<li>2.5 <a href="#u2.5">Avoiding Traffic Jams</a></li>
<li>2.6 <a href="#u2.6">Discovering What People Say about News
Stories</a></li>
<li>2.7 <a href="#u2.7">Exploring the Neighborhood</a></li>
<li>2.8 <a href="#u2.8">Sharing Vacation Photos with a
Friend</a></li>
<li>2.9 <a href="#u2.9">Finding Input and Output Documents for Test
Cases</a></li>
<li>2.10 <a href="#u2.10">Discovering Learning Resources</a></li>
<li>2.11 <a href="#u2.11">Finding Out New Things About
People</a></li>
<li>2.12 <a href="#u2.12">Browsing Patient Records</a></li>
<li>2.13 <a href="#u2.13">Finding Disjunct Conditions</a></li>
<li>2.14 <a href="#u2.14">Finding Film Soundtracks</a></li>
<li>2.15 <a href="#u2.15">Managing Personal Identities</a></li>
<li>2.16 <a href="#u2.16">Customizing Content Delivery</a></li>
<li>2.17 <a href="#u2.17">Building Ontology Tools</a></li>
<li>2.18 <a href="#u2.18">Working with Enterprise Web Services</a></li>
<li>2.19 <a href="#u2.19">Building Tables of Contents</a></li>
</ul>
</li>
<li>
<a href="#req">Requirements</a>
<ul>
<li>3.1 <a href="#r3.1">RDF Graph Pattern
Matching—Conjunction</a></li>
<li>3.2 <a href="#r3.2">Variable Binding Results</a></li>
<li>3.3 <a href="#r3.3">Extensible Value Testing</a></li>
<li>3.4 <a href="#r3.4">Subgraph Results</a></li>
<li>3.5 <a href="#r3.5">Local Queries</a></li>
<li>3.6 <a href="#r3.6">Optional Match</a></li>
<li>3.7 <a href="#r3.7">Limited Datatype Support</a></li>
<li>3.10 <a href="#r3.10">Result Limits</a></li>
<li>3.12 <a href="#r3.12">Streaming Results</a></li>
<li>3.13 <a href="#r3.13">RDF Graph Pattern
Matching—Disjunction</a></li>
<li>3.14 <a href="#r3.14">WSDL Protocol</a></li>
</ul>
</li>
<li>
<a href="#dobj">Design Objectives</a>
<ul>
<li>4.1 <a href="#d4.1">Human-friendly Syntax</a></li>
<li>4.2 <a href="#d4.2">Data Integration and Aggregation</a></li>
<li>4.3 <a href="#d4.3">Non-existent Triples</a></li>
<li>4.7 <a href="#d4.7">Bandwidth-efficient Protocol</a></li>
<li>4.8 <a href="#d4.8">Literal Search</a></li>
<li>4.9 <a href="#d4.9">Yes-No Queries</a></li>
<li>4.10 <a href="#d4.10">Addressable Query Results</a></li>
<li>4.11 <a href="#d4.11">Sorting Results</a></li>
</ul>
</li>
<li><a href="#relts">Related Technologies and Standards</a></li>
<li><a href="#ack">Acknowledgments</a></li>
<li><a href="#changes">Change Log</a></li>
</ol>
<h1><a name="intro" id="intro">1. Introduction</a></h1>
<p>The W3C's Semantic Web Activity is based on RDF's flexibility as a means
of representing data. While there are several standards covering RDF
itself, there has not yet been any work done to create standards for
querying or accessing RDF data. There is no formal, publicly standardized
language for querying RDF information. Likewise, there is no formal,
publicly standardized data access protocol for interacting with remote or
local RDF storage servers.</p>
<p>Despite the lack of standards, developers in commercial and in open
source projects have created <a href=
"http://www.w3.org/2001/11/13-RDF-Query-Rules/">many query languages for
RDF data</a>. But these languages lack both a common syntax and a common
semantics. In fact, the extant query languages cover a significant semantic
range: from declarative, SQL-like languages, to path languages, to rule or
production-like systems. The existing languages also exhibit a range of
extensibility features and built-in capabilities, including inferencing and
distributed query.</p>
<p>Further, there may be as many different methods of accessing remote RDF
storage servers as there are distinct RDF storage server projects. Even
where the basic access protocol is standardized in some sense—HTTP, SOAP,
or XML-RPC—there is little common ground upon which to develop generic
client support to access a wide variety of such servers.</p>
<p>The following use cases characterize some of the most important and most
common motivations behind the development of existing RDF query languages
and access protocols. The use cases, in turn, inform decisions about
<a href="#req">requirements</a>, that is, the critical features that a
standard RDF query language and data access protocol require, as well as
<a href="#dobj">design objectives</a> that aren't on the critical path.</p>
<h2><a name="uc" id="uc">2. Use Cases</a></h2>
<p>Each use case describes a user-oriented context in which the RDF query
language or protocol or both are used to solve a real problem. However, it
is not necessarily the case that the query language or data access protocol
will directly address all of these use cases. (Some of the use cases
contain illustrative RDF in Notation 3 form; consult <a href=
"http://www.w3.org/2000/10/swap/Primer">Primer: Getting into the semantic
web and RDF using N3</a> or <a href=
"http://infomesh.net/2002/notation3/">Notation3: A Rough Guide to N3</a>
for more details about N3.)</p>
<h3 class="uc"><a name="u2.1" id="u2.1">2.1 Finding an Email Address</a>
(Personal Information Management)</h3>
<p>George wants to send email to a person named "Johnny Lee Outlaw".
George's personal address book, which includes contact information for a
"Johnny Lee Outlaw", is stored in RDF using the <a href=
"http://xmlns.com/foaf/0.1/">FOAF Vocabulary Specification</a>.</p>
<div>
<pre class="rdf">
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
[]
foaf:name "Johnny Lee Outlaw" ;
foaf:mbox <mailto:jlow@example.com> .
</pre><br />
<span class="rdf-caption">Figure One: A Fragment of a FOAF Address
Book</span>
</div>
<p>George's email client queries his local address book service and, since
there is only one match, uses the query's result to populate the
<code>To:</code> field.</p>
<p><strong>Motivates:</strong> <a href="#r3.1">RDF Graph Pattern
Matching</a>, <a href="#r3.2">Variable Binding Results</a>.</p>
<h3 class="uc"><a name="u2.2" id="u2.2">2.2 Finding Information about
Motorcycle Parts</a> (Supply Chain Management)</h3>
<p>Endeavour, a dealer specializing in British motorcycles, maintains a
database that describes spare and replacement parts, including their
properties and relationships. Ev, a repair person who specializes in
Triumph bikes, is working on an ailing Speed Triple motorcycle when a
diagnostic tool produces a report identifying a defect in the fuel
management system.</p>
<div>
<pre class="rdf">
@prefix triumph: <http://triumph.example/schema/#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
<http://triumph.example/part/0d92ie433>
rdf:type triumph:part ;
rdfs:label "Accelerator Cable MK3" ;
triumph:depends-on <http://triumph.example/part/329i2dk39> ;
triumph:part-for <http://triumph.example/2004/SpeedTriple> ;
triumph:part-number "LCD 100-04BSPT" .
<http://triumph.example/part/329i2dk39>
rdfs:label "Mounting Bracket" ;
triumph:requires
[ triumph:has-number "4" ;
triumph:part-number "149028ab-MT" ;
triumph:type triumph:screwx
] .
</pre><br />
<span class="rdf-caption">Figure Two: A Fragment of the Endeavour Parts
Database</span>
</div>
<p>Ev uses a query interface to the parts database to ask about the
defective part. In response to her query, Ev receives a human-readable
description of the part, which provides enough information to obtain a
replacement part and tells her about other, dependent parts that must be
replaced at the same time.</p>
<p><strong>Motivates:</strong> <a href="#r3.4">Subgraph Results</a>,
<a href="#r3.5">Optional Match</a>, <a href="#d4.1">Human-friendly
Syntax</a>.</p>
<h3 class="uc"><a name="u2.3" id="u2.3">2.3 Finding Unknown Media
Objects</a> (Publishing)</h3>
<p>Smiley works for a multinational media conglomerate. As part of his job
as an editor of foreign market compilations, he needs to be notified
whenever the conglomerate's knowledge bases contain information about new
media objects—books, movies, and pop music—matching various properties:
title, author, and price point.</p>
<p>Smiley uses his web browser to create a query that will be executed
regularly against the conglomerate's knowledge bases. Whenever there are
new matches for Smiley's query, he receives an email with URIs to resources
about the new matches; and Smiley's personal RSS feed is also updated with
the new matches, since he uses an RSS aggregator to gather news every
day.</p>
<div>
<pre class="rdf">
@prefix baf: <http://big-accounting-firm.example/scheme/1.0/#> .
@prefix bmc: <http://big-media-conglomerate.example/ontology/#> .
@prefix dc: <http://purl.org/dc/elements/1.1/> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
[]
baf:dollarPrice "29.99" ;
bmc:objectName "J to the LO" ;
dc:author <http://big-media.example/author/1929/> .
</pre><br />
<span class="rdf-caption">Figure Three: Big Media Conglomerate Knowledge
Base</span>
</div>
<p>Since Smiley's query will operate over knowledge bases structured by at
least four different ontologies—the result of his conglomerate's rapid
expansion—Karla, the staff programmer for Smiley's group, makes sure that
knowledge bases in question contain appropriate
<code>rdfs:subPropertyOf</code> assertions. For example, Smiley's query
uses the predicate <code>media:ObjectName</code>, which will also find
properties like <code>dc:title</code>, <code><a href=
"http://www.doi.org/">doi</a>:title</code>, and <code><a href=
"http://www.loc.gov/standards/mods/">mods</a>:titleInfo</code>.</p>
<p><strong>Motivates:</strong> <a href="#d4.1">Human-friendly Syntax</a>,
<a href="#d4.2">Data Integration and Aggregation</a>.</p>
<h3><a name="u2.4" id="u2.4">2.4 Monitoring News Events</a>
(Multimedia)</h3>
<p>Kate wants to see all the television programs that feature information
about the Japanese baseball player Ichiro. She wants her personal digital
recorder (PDR) to record every television show about Japanese baseball
automatically using the Electronic Program Guides (EPGs). She also wants an
index page for each week's recorded items.</p>
<p>Her RDF-enabled PDR periodically executes a query against the RDF
version of its EPGs, and continues to execute the query every day for new
items to record.</p>
<p><strong>Motivates:</strong> <a href="#r3.10">Result Limits</a>, <a href=
"#d4.2">Data Integration and Aggregation</a>, <a href="#d4.10">Addressable
Query Results</a>.</p>
<h3 class="uc"><a name="u2.5" id="u2.5">2.5 Avoiding Traffic Jams</a>
(Transportation)</h3>
<p>Niel has to drive every day from home to his office during heavy rush
hour traffic in Atlanta, GA, in his new car, which has Bluetooth and
wireless Internet access. Using his cell phone, Niel requests that his car
query public RDF storage servers on the Web for a description of current
Atlanta road construction projects, traffic jams, and roads affected by
inclement weather.</p>
<p>Based on the information retrieved efficiently from the public RDF
servers, Niel uses the mapping program in his cell phone to plan a
different route to work, cutting his commute time by 10%.</p>
<p><strong>Motivates:</strong> <a href="#d4.7">Bandwidth-efficient
Protocol</a>, <a href="#r3.10">Result Limits</a>.</p>
<h3 class="uc"><a name="u2.6" id="u2.6">2.6 Discovering What People Say
about News Stories</a> (Publishing)</h3>
<p>Abelard, an independent publisher of web publications, wants to query
RSS feed aggregators in order to track RDF assertions people make about
articles and stories in his publications. Abelard's client software
includes support for three different RDF query languages.</p>
<p>Heloise manages one of the servers that Abelard wants to query. Her
server publishes a machine readable description of its capabilities,
including the query languages it supports, in RDF. Abelard's client asks
Heloise's server whether it supports his preferred query language.
Abelard's client software also negotiates with the other servers and uses a
common transport protocol to retrieve the results of his queries.</p>
<p><strong>Motivates:</strong> <a href="#d4.1">Human-friendly Syntax</a>,
<a href="#d4.2">Data Integration and Aggregation</a>, <a href=
"#d4.9">Yes-No Queries</a>.</p>
<h3 class="uc"><a name="u2.7" id="u2.7">2.7 Exploring the Neighborhood</a>
(Tourism)</h3>
<p>José knows that the U.S. Census Bureau provides interesting geographic
data in its public domain <a href=
"http://www.census.gov/geo/www/tiger/">TIGER</a> database. José attends a
conference in Washington, DC, at the new convention center, and he stays in
a hotel nearby. José wants to find out the latitude, longitude, name, and
type of everything within one mile of the convention center, as well as all
events occurring during his stay, so that he can plan his meals and
sightseeing time accordingly.</p>
<p>Rather than working with the TIGER database files directly, José sends a
query to the Census Bureau's new RDF storage server and requests that his
client pass the query results to an XSLT transformation service so that he
can print the resulting XHTML.</p>
<p><strong>Motivates:</strong> <a href="#r3.3">Extensible Value
Testing</a>, <a href="#r3.7">Limited Datatype Support</a>, <a href=
"#d4.1">Human-friendly Syntax</a>.</p>
<h3 class="uc"><a name="u2.8" id="u2.8">2.8 Sharing Vacation Photos with a
Friend</a> (Personal Information Management)</h3>
<p>Frannie and Zoe, old college friends, live in different countries and
keep in daily contact via IRC. Zoe wrote an IRC bot that they use to make
assertions—which the bot stores as RDF—about photographs of their family,
friends, and vacations. Frannie wants to be able to republish some of these
assertions in a human readable form on her weblog. Zoe tells her about a
server that accepts and agrees to host documents that describe what they
say about web resources, and their IRC bot sends those documents
periodically to the server.</p>
<p>Frannie programs her weblog software to query the server that hosts
their annotations for vacation images that co-depict her family members
with Zoe's family members, as well as for things Zoe and Franny have said
about those images. Frannie uses the XSLT processor built into her weblog
software to transform the query results into XHTML for display in her
weblog.</p>
<p><strong>Motivates:</strong> <a href="#r3.2">Variable Binding
Results</a>, <a href="#d4.2">Data Integration and Aggregation</a>, <a href=
"#d4.3">Non-existent Triples</a>,.</p>
<h3 class="uc"><a name="u2.9" id="u2.9">2.9 Finding Input and Output
Documents for Test Cases</a> (Software Development)</h3>
<p>Nada, a Semantic Web developer, has a bug report from a valued user
indicating that a software tool is incorrectly emitting the N3
representation of some of the RDF core test cases. Nada wants to create a
list of input and output documents for each of the approved test cases,
filtering only for those which have an "approved" status, from the RDF core
test suite. The list of tests resides in a single file.</p>
<p>Nada can process the RDF core manifest file in such a way as to write
one input-output pair per line to standard-out; another program can then be
written to read, write, and check the input document.</p>
<p><strong>Motivates:</strong> <a href="#r3.1">RDF Graph Pattern
Matching</a>, <a href="#r3.2">Variable Results</a>, <a href="#r3.5">Local
Queries</a>.</p>
<h3 class="uc"><a name="u2.10" id="u2.10">2.10 Discovering Learning
Resources</a> (Instructional Technology)</h3>
<p>Erasmus Jones, a professor, wants to find some learning materials for
his seminar on Renaissance humanism. He is using a recommended web site
that provides descriptions of learning materials; he performs a search at
the site, chosing the general subject area, student learning level, and
provides some keywords. The results include materials returned from
multiple learning repositories, where the subject and learning levels have
been matched across multiple educational metadata vocabularies, including
predicates from the <a href="http://dublincore.org/documents/dces/">Dublin
Core Metadata Element Set</a> and the <a href=
"http://www.cetis.ac.uk/profiles/uklomcore">UK Learning Object Metadata
Framework</a> specifications.</p>
<p><strong>Motivates:</strong> <a href="#d4.2">Data Integration and
Aggregation</a> .</p>
<h3 class="uc"><a name="u2.11" id="u2.11">2.11 Finding Out New Things About
People (Social Network Analysis)</a></h3>
<p>Esther, a programmmer for a new social networking site based on <a href=
"http://xmlns.com/foaf/0.1/">FOAF</a>, has written an <a href=
"http://www.hackdiary.com/archives/000030.html">RDF crawler</a> which
follows <code>foaf:knows</code> links to determine the publicly available
properties of new people it will invite into the network. While processing
a new FOAF resource, it finds an <code>rdf:Property</code> referring to a
URI that it has not seen before. The crawler queries an ontology server to
see if the property's domain(s) and range(s) are ones that it has already
encountered, so that it can track where it first discovered this property
and use the property in future searches.</p>
<p><strong>Motivates:</strong> <a href="#d4.2">Data Integration and
Aggregation</a>.</p>
<h3 class="uc"><a name="u2.12" id="u2.12">2.12 Browsing Patient Records
(Health Care)</a></h3>
<p>Peter is developing a medical knowledge base using OWL/RDF in
collaboration with medical domain experts. The knowledge base is used
within <a href="http://xml.coverpages.org/hl7PRA.html">electronic patient
records</a>. To facilitate collaboration and avoid duplication, the team is
using a <a href=
"http://ebxmlrr.sourceforge.net/presentations/xmlEurope2004/04-02-02.pdf">federated
ebXML Registry</a> to store the knowledge base they are building.</p>
<p>When adding a new concept to the knowledge base, Peter uses a registry
browser application to search the ebXML Registry for similar or related
concepts. The <a href=
"http://ebxmlrr.sourceforge.net/3.0/registryBrowser/">registry browser</a>
allows Peter to choose a <a href=
"http://ebxmlrr.sourceforge.net/3.0/registryBrowser/discovery.html#Adhoc%20Queries">
parameterized query</a> from a set of preconfigured parameterized queries
and offers a form that Peter uses to enter the query parameters.</p>
<p>Peter enters a few parameters and issues the query. The ebXML Registry
returns a large number of <a href=
"http://ebxmlrr.sourceforge.net/3.0/registryBrowser/discovery.html#Search%20Results%20Panel">
matching results</a>. Upon viewing the results, Peter issues a more
specific search to find more relevent information. After several such
refinements, he has found the concepts that are most relevant to his
concept. He then <a href=
"http://ebxmlrr.sourceforge.net/3.0/registryBrowser/browsing.html">drills
down and browses</a> these concepts, as well as their related concepts and
metadata, to determine whether to add his new concept.</p>
<p><strong>Motivates:</strong> <a href="#r3.1">RDF Graph Pattern
Matching</a>, <a href="#r3.2">Variable Binding Results</a>, <a href=
"#r3.12">Streaming Results</a>.</p>
<h3 class="uc"><a name="u2.13" id="u2.13">2.13 Finding Disjunct Conditions
(Market Research)</a></h3>
<p>Lyndie works for a firm that creates market research reports for
corporations that have contracts with the US federal government. She has
access to an RDF repository, which contains information about accounting
firms, corporations, and their customers:</p>
<div>
<pre class="rdf">
@prefix baf: <http://big-accounting-firm.example/scheme/1.0/#>.
@prefix xsd: <http://www.w3.org/2001/XMLSchema#>.
<http://www.pwc.com/> baf:hasName "PriceWaterhouseCoopers"^^xsd:string.
<http://www.boeing.com/> baf:hasName "Boeing"^^xsd:string.
<http://www.labor.gov/> baf:hasName "US Department of Labor"^^xsd:string.
<http://www.pwc.com/> baf:accountsFor <http://www.boeing.com/>.
<http://www.boeing.com/> baf:hasCustomer <http://www.labor.gov/> .
</pre><br />
<span class="rdf-caption">Figure Four: Accounting Repository
Fragment</span>
</div>
<p>Lyndie wants to query this RDF repository in order to find the names of
accounting firms that do accounts for suppliers of the Department of Labor
or that do accounts for the Department of Labor itself.</p>
<p><strong>Motivates:</strong> <a href="#r3.13">RDF Graph Pattern
Matching—Disjunction</a>.</p>
<h3 class="uc"><a name="u2.14" id="u2.14">2.14 Finding Film Soundtracks
(Data Aggregation)</a></h3>
<p>Marty wants to learn which of the ten biggest grossing Hollywood movies
of all time also had soundtracks among the ten biggest grossing film
soundtracks of all time. Imagine that some future version of the IMDB site
exposes its information about movies as RDF. Next, imagine that the
machine-readable metadata about music at <a href=
"http://www.musicbrainz.org/MM/">MusicBrainz</a> includes information about
album sales. Marty then writes a query to find the titles of the ten
biggest grossing films. He uses the results of that query to query
MusicBrainz in order to filter the films that did not have top 10
soundtracks.</p>
<p><strong>Motivates:</strong> <a href="#d4.2">Data Integration and
Aggregation</a> .</p>
<h3 class="uc"><a name="u2.15" id="u2.15">2.15 Managing Personal Identity
(Personal Information Management)</a></h3>
<p>Mister X, a professional and anonymous controversialist, manages two
distinct personae using the <a href="http://xmlns.com/foaf/0.1/">FOAF
Vocabulary Specification</a>. Mister X maintains three separate
<code>foaf:PersonalProfileDocument</code> (PPD) documents describing his
controversial personae. Each profile is available at a different public URI
on the Web, and each contains RDF statements describing Mister X and his
personae as distinct resources.</p>
<p>Matthias, an enterprising RDF hacker, periodically runs <a href=
"http://www.hackdiary.com/archives/000030.html">an RDF crawler</a> which
harvests Mister X's PPDs, keeping track of the source URI for each RDF
triple together with X's personae resources scope information. Matthias has
also built a public Web interface to publish the RDF triples resulting from
the crawling process, together with all the source information associated
with the harvested RDF triples.</p>
<p>A programmer, Johanna, employed by NextBigDeal Inc., is asked to build a
next generation personal information aggregator which must be able to
execute RDF queries over Matthias's RDF data. Johanna's application must be
able to present and redistribute different people's information grouped by
each persona, as well as by <code>foaf:knows</code> relationships.</p>
<p><strong>Motivates:</strong> <a href="#d4.2">Data Integration and
Aggregation</a>.</p>
<h3 class="uc"><a name="u2.16" id="u2.16">2.16 Customizing Content Delivery
(Device Independence)</a></h3>
<div>
<pre class="rdf">
@prefix prf: <http://www.openmobilealliance.org/tech/profiles/uaprof/ccppschema-20021212#HardwarePlatform>.
@prefix xsd: <http://www.w3.org/2001/XMLSchema#>.
[]
prf:BitsPerPixel "8"^^xsd:int ;
prf:ColorCapable "true"^^xsd:boolean ;
prf:CPU "Arm 7" ;
prf:ImageCapable "true"^^xsd:boolean ;
prf:ScreenSize "101x80" ;
prf:SoundOutputCapable "false"^^xsd:boolean ;
prf:Vendor "Panasonic" .
</pre><br />
<span class="rdf-caption">Figure Five: Panasonic GD67 Profile
Fragment</span>
</div>
<p>Hill, an avid motorcycle time trialist, needs directions to the
racetrack. He uses his Panasonic mobile phone to request a Web resource
that has directions to the track. His phone includes in its request a URI
to <a href="http://mobileinternet.panasonicbox.com/UAprof/GD67/04.xml">an
RDF profile of its capabilities</a>, as well as a diff of its current
state, which may add to, hide, or override some of the information in the
standard profile.</p>
<p>The origin server must compute the final state of Hill's mobile phone
profile by dereferencing the URI that identifies the standard profile and
then applying the device-specific diff. Then, in order to return a
device-specific representation of the resource Hill requested, the origin
server issues an RDF query against the device profile graph to determine
whether to return a color map, a sound file, or plain text directions in
its response. Since Hill's device is capable of displaying color images,
the origin server returns a representation of the requested resource which
includes a link to a color image.</p>
<p><strong>Motivates:</strong> <a href="#d4.2">Data Aggregation and
Integration</a>, <a href="#d4.9">Yes-No Queries</a>.</p>
<h3 class="uc"><a name="u2.17" id="u2.17">2.17 Building Ontology Tools
(Semantic Web)</a></h3>
<p>Aditya, a Semantic Web researcher who specializes in building ontology
tools, is working on <a href="http://www.mindswap.org/2004/SWOOP/">a new
hypermedia-influenced ontology editor</a>, which is meant for navigating
existing and creating new OWL ontologies. Aditya wants to use an RDF query
language to interact with OWL ontologies in order to do queries like
finding equivalent classes, subclasses, superclasses, and disjoint classes,
object and datatype properties, and individuals.</p>
<p>Some parts of the ontology editor require the transitive closure of the
query and other parts do not. Queries for equivalent, sub- and superclasses
are useful in creating class tree hierarchies, which is a central feature
in an ontology editor. Constructing a subclass hierarchy allows the
ontology to support additional queries like finding the nearest common
ancestor of two classes. Aditya also wants to be able to execute queries to
find object and datatype properties, as well as individuals, in order to
provide instance support in the ontology editor; property queries, for
example, provide slots for frame-centric views.</p>
<p><strong>Motivates:</strong> <a href=
"http://www.w3.org/2003/12/swa/dawg-charter#extensibilty">Extensibility
Mechanism</a>.</p>
<h3 class="uc"><a name="u2.18" id="u2.18">2.18 Working with
Enterprise Web Services (Web Services)</a></h3>
<p>Ryu, a .NET programmer, is tasked with aggregating a wide range of
data from a variety of enterprise sources, including query results
from an RDF triple store. All of the data services, including the
RDF triple store, have WSDL descriptions which Ryu's Visual Studio
environment reads and presents to him as libraries. Ryu writes
ordinary code to grab the data from these sources, including data
results from queries sent to the RDF triple store. He also writes
code to merge these data together in an application-specific way.
</p>
<p>Eventually Ryu's company decides to change the protocol for
interacting with the RDF triple store server from pure HTTP to SOAP
over HTTP. All Ryu has to do is update the WSDL describing the RDF
triple store, and the rest of his code is unchanged..</p>
<p><strong>Motivates:</strong> <a href="#r3.14">WSDL Protocol</a>.</p>
<h3 class="uc"><a name="u2.19" id="u2.19">2.19 Building a Table of
Contents (Publishing)</a></h3>
<p>Leigh, a programmer for a large publishing house, uses RDF to
store data and metadata about books and journals. Leigh uses RDF
query language to retrieve the first three articles associated with an issue and
sort them by page number; to retrieve all issues associated with a
journal and sort them by publication date; to retrieve the last 10 articles
bookmarked by a user and sort them by journal name or date
bookmarked; to retrieve all journals within a subject area and sort
them by name; and to retrieve all articles written by an author and
sort them by publication date.</p>
<p><strong>Motivates:</strong> <a href="#r3.10">Result Limits</a>, <a href= "#d4.11">Sorting
Results</a>.</p>
<h2 class="req"><a name="req" id="req">3.</a> Requirements</h2>
<p>Technical requirements are features or characteristics of either the
query language or data access protocol (or, in some cases, of both) that
are expected to be in the specification.</p>
<h3 class="req"><a name="r3.1" id="r3.1">3.1 RDF Graph Pattern
Matching—Conjunction</a></h3>
<p>The query language must include the capability to restrict matches on a
queried graph by providing a graph pattern, which consists of one or more
RDF triple patterns, to be satisfied in a query.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://lists.w3.org/Archives/Public/public-rdf-dawg/2004AprJun/0385.html">2004-05-11</a>.</p>
<h3 class="req"><a name="r3.2" id="r3.2">3.2 Variable Binding
Results</a></h3>
<p>It must be possible for queries to return zero or more bindings of
variables. Each set of bindings is one way that the query can be satisfied
by the queried graph.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://lists.w3.org/Archives/Public/public-rdf-dawg/2004AprJun/0385.html">2004-05-11</a>.</p>
<h3 class="req"><a name="r3.3" id="r3.3">3.3 Extensible Value
Testing</a></h3>
<p>The query language must make it possible—whether through function calls,
namespaces, or in some other way—to calculate and test values
extensibly.</p>
<p>Many application domains have specific value testing requirements; for
example: the concept of "distance" in geospatial data or calculating the
gravitational attraction of two masses, given their mass and the distance
between them. Value testing may be more efficient when domain specific
functions are available for use.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://lists.w3.org/Archives/Public/public-rdf-dawg/2004AprJun/0330.html">2004-05-04</a>.</p>
<h3 class="req"><a name="r3.4" id="r3.4">3.4 Subgraph Results</a></h3>
<p>It must be possible for query results to be returned as a subgraph of
the original queried graph.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://lists.w3.org/Archives/Public/public-rdf-dawg/2004AprJun/0641.html">2004-06-15</a></p>
<h3 class="req"><a name="r3.5" id="r3.5">3.5 Local Queries</a></h3>
<p>The query language must be suitable for use in accessing local RDF
data—that is, from the same machine or same system process.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://lists.w3.org/Archives/Public/public-rdf-dawg/2004AprJun/0330.html">2004-05-04</a>.</p>
<h3 class="req"><a name="r3.6" id="r3.6">3.6 Optional Match</a></h3>
<p>It must be possible to express a query that does not fail when some
specified part of the query fails to match. Any such triples matched by
this optional part, or variable bindings caused by this optional part, can
be returned in the results, if requested.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://www.w3.org/2001/sw/DataAccess/ftf2">2004-07-15</a>.</p>
<h3 class="req"><a name="r3.7" id="r3.7">3.7 Limited Datatype
Support</a></h3>
<p>The query language must include support for a subset of W3C XML Schema
datatypes and operations on those datatypes.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://lists.w3.org/Archives/Public/public-rdf-dawg/2004AprJun/0385.html">2004-05-11</a>.</p>
<h3 class="req"><a name="r3.10" id="r3.10">3.10 Result Limits</a></h3>
<p>It must be possible to specify an upper bound on the number of query
results returned.</p>
<p><span class="note">(Note: The Working Group has <a href=
"http://www.w3.org/Search/Mail/Public/search?keywords=results+limit+sorting&hdr-1-name=subject&hdr-1-query=&index-grp=Public__FULL&index-type=t&type-index=public-rdf-dawg">
discussed</a> and is aware of the connection between result limits and
result sorting, as well as the implementation costs of sorting and the
tradeoffs between client and server computing power per user.)</span></p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://www.w3.org/2001/sw/DataAccess/ftf2">2004-07-15</a>.</p>
<h3 class="req"><a name="r3.12" id="r3.12">3.12 Streaming Results</a></h3>
<p>It must be possible, when returning multiple unordered results, for the
client to request that results be streamed. When the client requests
streaming results, all the data in one result must be available to the
client before all the data for the next result.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://lists.w3.org/Archives/Public/public-rdf-dawg/2004AprJun/0799.html">2004-06-29</a>.</p>
<h3 class="req"><a name="r3.13" id="r3.13">3.13 RDF Graph Pattern
Matching—Disjunction</a></h3>
<p>The query language must include the capability to restrict matches on a
queried graph based on a disjunction of graph patterns, at least one of
which must be satisfied.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://www.w3.org/2001/sw/DataAccess/ftf2">2004-07-16</a>.</p>
<h3 class="req"><a name="r3.14" id="r3.14">3.14 WSDL Protocol</a></h3>
<p>The protocol -- including its interfaces, their operations, results, and types -- must be described using WSDL.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span>
<a href="http://www.w3.org/2001/sw/DataAccess/ftf5-bos.html#item_03">2005-02-28</a>>.</p>
<h2 class="dobj"><a name="dobj" id="dobj">4.</a> Design Objectives</h2>
<p>Design objectives, which may be features or characteristics of the
eventual design, differ from requirements in that the specification may be
complete if none, some, or all of them are achieved.</p>
<h3 class="do"><a name="d4.1" id="d4.1">4.1 Human-friendly Syntax</a></h3>
<p>There must be a text-based form of the query language which can be read
and written easily by users of the language.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://www.w3.org/2001/sw/DataAccess/ftf2">2004-07-15</a>.</p>
<h3 class="do"><a name="d4.2" id="d4.2">4.2 Data Integration and
Aggregation</a></h3>
<p>RDF can be used for data integration and aggregation. Often RDF
repositories are built by merging RDF triples from one or more sources,
including other RDF repositories or non-RDF data sources converted to RDF.
Such aggregations can be real or virtual. It is always possible that a
triple exists in multiple sources.</p>
<ol>
<li>
<p>It must be possible for the query language and protocol to allow an
RDF repository to expose the sources of RDF triples.</p>
</li>
<li>
<p>It should be possible to constrain a query with regard to the source
or sources of a triple or triple pattern.</p>
</li>
<li>
<p>It should be possible for the query language and protocol to allow
for queries against multiple RDF graphs, including graphs published by
different repositories. When more than one RDF graph is selected, the
result is as if the query had been executed against the <a href=
"http://www.w3.org/TR/rdf-mt/#graphdefs">merge of the selected RDF
graphs</a>.</p>
</li>
</ol>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://www.w3.org/2001/sw/DataAccess/ftf3-brs">2004-09-16</a>.</p>
<h3 class="do"><a name="d4.3" id="d4.3">4.3 Non-existent Triples</a></h3>
<p>It must be possible to query for the non-existence of one or more
triples or triple patterns in the queried graph.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://www.w3.org/2001/sw/DataAccess/ftf2">2004-07-15</a>.</p>
<h3 class="do"><a name="d4.7" id="d4.7">4.7 Bandwidth-efficient
Protocol</a></h3>
<p>The access protocol design shall address bandwidth utilization issues;
that is, it shall allow for at least one result format that does not make
excessive use of network bandwidth for a given collection of results.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span>.</p>
<h3 class="do"><a name="d4.8" id="d4.8">4.8 Literal Search</a></h3>
<p>It should be possible for a query to perform substring searches of RDF
string literals.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://www.w3.org/2001/sw/DataAccess/ftf2">2004-07-16</a>.</p>
<h3 class="dp"><a name="d4.9" id="d4.9">4.9 Yes-No Queries</a></h3>
<p>It must be possible to express yes-no queries directly in the query
language.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://www.w3.org/2001/sw/DataAccess/ftf2">2004-07-15</a>.</p>
<h3 class="dp"><a name="d4.10" id="d4.10">4.10 Addressable Query
Results</a></h3>
<p>A common pattern of access is to send a query, <a href=
"http://www.w3.org/2001/tag/doc/whenToUseGet.html">which is like asking a
question</a>, to a remote service which evaluates it and returns the answer
or results. This access pattern fits naturally into the architecture of the
Web by making query results addressable resources.</p>
<p>It must be possible for query results to be addressed in URI space.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a href=
"http://www.w3.org/2001/sw/DataAccess/ftf2">2004-07-16</a>.</p>
<h3 class="dp"><a name="d4.11" id="d4.11">4.11 Sorting Results</a></h3>
<p>Tthe query language should be able to express sort orderings on
query results.</p>
<p><strong>Status:</strong> <span class="accept">Accepted</span> <a
href=
"http://lists.w3.org/Archives/Public/public-rdf-dawg/2005JanMar/0358.html">2004-03-15</a>.</p>
<h1><a name="relts" id="relts">5. Related Technologies and
Standards</a></h1>
<p>See the survey of existing RDF query language implementations: "<a href=
"http://www.w3.org/2001/11/13-RDF-Query-Rules/">RDF Query Survey</a>", as
well as the "<a href=
"http://www.w3.org/2001/11/13-RDF-Query-Rules/terms">RDF Query and Rules
Framework</a>".</p>
<ul>
<li><a href="http://www.w3.org/2001/sw/RDFCore/">RDF Core</a></li>
<li><a href="http://www.w3.org/2001/sw/WebOnt/">OWL</a></li>
<li>SQL-like, rule-like, and path-like RDF query languages</li>
<li>SQL</li>
<li><a href=
"http://www.xml.com/pub/a/2001/04/25/prologrdf/">Prolog</a></li>
<li><a href="http://www.topicmaps.org/xtm/">XML Topic Maps</a></li>
<li><a href="http://www.w3.org/XML/Query">XQuery</a></li>
<li><a href="http://www.w3.org/TR/xptr-framework/">XPointer</a></li>
<li><a href="http://www.w3.org/2000/xp/Group/">SOAP/XMLP</a> and <a href=
"http://www.intertwingly.net/stories/2002/07/20/restSoap.html">REST</a></li>
<li><a href="http://web.resource.org/rss/1.0/">RDF Site Summary (RSS)
1.0</a>, <a href="http://blogs.law.harvard.edu/tech/rss">RSS 2.0</a>,
<a href="http://www.atomenabled.org/developers/api/atom-api-spec.php">The
Atom API</a>, <a href=
"http://www.atomenabled.org/developers/syndication/atom-format-spec.php">The
Atom Syndication Format</a></li>
<li><a href="http://www.w3.org/TR/wsdl20/">WSDL 2.0</a>, <a href=
"http://www.w3.org/TR/xforms/">XForms</a>, <a href=
"http://www.markbaker.ca/2003/05/RDF-Forms/">RDF Forms</a></li>
</ul>
<h1><a name="ack" id="ack">6. Acknowledgments</a></h1>
<p>The editor acknowledges all of the members of the <a href=
"http://www.w3.org/2001/sw/DataAccess/">Data Access Working Group</a> for
aid and assistance in preparing the present document, especially Andy
Seaborne, Yoshio Fukushige, Bryan Thompson, Howard Katz, Dave Beckett, Dan
Connolly, and Eric Prud'hommeaux. The editor also acknowledges the support
of his University of Maryland MIND Lab colleagues, especially Bijan Parsia
and James Hendler.</p>
<h1><a name="changes" id="changes">7. Change Log</a></h1>
<p>Changes since the <a
href="http://www.w3.org/TR/2004/WD-rdf-dawg-uc-20040802/">previous
Oct 2004 draft</a> include:</p>
<ul>
<li>added <a href="#d4.11">4.11 Sorting Results</a> objective and
supporting use case <a href="#u2.19">2.19 Building a Table of
Contents (Publishing)</a></li>
<li>added <a href="#r3.14">3.14 WSDL Protocol</a> requirement and
supporting use case <a href="#u2.18">2.18 Working with Enterprise
Web Services (Web Services)</a></li>
</ul>
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