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    <title>RDFa 1.1 Primer</title>
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/* --- SYNTAX HIGHLIGHTING --- */
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</style><link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel="stylesheet" type="text/css" charset="utf-8" /></head>
  <body style="display: inherit; "><div class="head"><p><a href="http://www.w3.org/"><img width="72" height="48" src="http://www.w3.org/Icons/w3c_home" alt="W3C" /></a></p><h1 property="dcterms:title" class="title" id="title">RDFa 1.1 Primer</h1><h2 property="bibo:subtitle" id="subtitle">Rich Structured Data Markup for Web Documents</h2><h2 property="dcterms:issued" datatype="xsd:dateTime" content="2011-12-08T10:57:36+0000" id="w3c-working-draft-08-december-2011"><acronym title="World Wide Web Consortium">W3C</acronym> Working Draft 08 December 2011</h2><dl><dt>This version:</dt><dd><a href="http://www.w3.org/TR/2011/WD-rdfa-primer-20111208/">http://www.w3.org/TR/2011/WD-rdfa-primer-20111208/</a></dd><dt>Latest published version:</dt><dd><a href="http://www.w3.org/TR/rdfa-primer/">http://www.w3.org/TR/rdfa-primer/</a></dd><dt>Latest editor's draft:</dt><dd><a href="http://www.w3.org/2010/02/rdfa/sources/rdfa-primer/">http://www.w3.org/2010/02/rdfa/sources/rdfa-primer/</a></dd><dt>Previous version:</dt><dd><a rel="dcterms:replaces" href="http://www.w3.org/TR/2011/WD-rdfa-primer-20110419/">http://www.w3.org/TR/2011/WD-rdfa-primer-20110419/</a></dd><dt>Editors:</dt><dd rel="bibo:editor"><span typeof="foaf:Person"><a rel="foaf:homepage" property="foaf:name" content="Ben Adida" href="http://ben.adida.net/">Ben Adida</a>, <a rel="foaf:workplaceHomepage" href="http://creativecommons.org/">Creative Commons</a></span>
</dd>
<dd rel="bibo:editor"><span typeof="foaf:Person"><a rel="foaf:homepage" property="foaf:name" content="Ivan Herman" href="http://www.w3.org/People/Ivan/">Ivan Herman</a>, <a rel="foaf:workplaceHomepage" href="http://www.w3.org"><acronym title="World Wide Web Consortium">W3C</acronym></a></span>
</dd>
<dd rel="bibo:editor"><span typeof="foaf:Person"><a rel="foaf:homepage" property="foaf:name" content="Manu Sporny" href="http://manu.sporny.org">Manu Sporny</a>, <a rel="foaf:workplaceHomepage" href="http://digitalbazaar.com/">Digital Bazaar</a></span>
</dd>
<dt>Author:</dt><dd rel="dcterms:contributor"><span typeof="foaf:Person"><a rel="foaf:homepage" property="foaf:name" content="Mark Birbeck" href="http://webbackplane.com/mark-birbeck">Mark Birbeck</a>, <a rel="foaf:workplaceHomepage" href="http://webbackplane.com/">webBackPlane.com</a></span>
</dd>
<dt>Alternates:</dt><dd><a href="diff-20110419.html">Diff-marked version</a></dd>
</dl><p class="copyright"><a rel="license" href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2010-2011 <span rel="dcterms:publisher"><span typeof="foaf:Organization"><a rel="foaf:homepage" property="foaf:name" content="World Wide Web Consotrium" href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup></span></span> (<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. <acronym title="World Wide Web Consortium">W3C</acronym> <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><hr /></div>
    <div id="abstract" class="introductory section" property="dcterms:abstract" datatype="" typeof="bibo:Chapter" about="#abstract"><h2>Abstract</h2>
      <p> The last couple of years have witnessed a fascinating
        evolution: while the Web was initially built predominantly for
        human consumption, web content is increasingly consumed by
        machines which expect some amount of structured data. Sites have
        started to identify a page’s title, content type, and preview
        image to provide appropriate information in a user’s newsfeed
        when she clicks the “Like” button. Search engines have started
        to provide richer search results by extracting fine-grained
        structured details from the Web pages they crawl. In turn, web
        publishers are producing increasing amounts of structured data
        within their Web content to improve their standing with search
        engines. </p>
      <p> A key enabling technology behind these developments is the
        ability to add structured data to HTML pages directly. RDFa
        (Resource Description Framework in Attributes) is a technique
        that allows just that: it provides a set of markup attributes to
        augment the visual information on the Web with machine-readable
        hints. In this Primer, we show how to express data using RDFa in
        HTML, and in particular how to mark up existing human-readable
        Web page content to express machine-readable data. </p>
      <p> This document provides only a Primer to RDFa. The complete
        specification of RDFa, with further examples, can be found in
        the RDFa 1.1 Core [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>], the XHTML+RDFa 1.1
        [<cite><a class="bibref" rel="biblioentry" href="#bib-XHTML-RDFA">XHTML-RDFA</a></cite>], and the HTML5+RDFa 1.1 [<cite><a class="bibref" rel="biblioentry" href="#bib-HTML-RDFA">HTML-RDFA</a></cite>]
        specifications. </p>
    </div><div id="sotd" class="introductory section" typeof="bibo:Chapter" about="#sotd"><h2>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 <acronym title="World Wide Web Consortium">W3C</acronym> publications and the latest revision of this technical report can be found in the <a href="http://www.w3.org/TR/"><acronym title="World Wide Web Consortium">W3C</acronym> technical reports index</a> at http://www.w3.org/TR/.</em></p><p>This document was published by the <a href="http://www.w3.org/2010/02/rdfa/">RDF Web Applications Working Group</a> as a Working Draft. This document is intended to become a <acronym title="World Wide Web Consortium">W3C</acronym> Recommendation. If you wish to make comments regarding this document, please send them to <a href="mailto:public-rdfa-wg@w3.org">public-rdfa-wg@w3.org</a> (<a href="mailto:public-rdfa-wg-request@w3.org?subject=subscribe">subscribe</a>, <a href="http://lists.w3.org/Archives/Public/public-rdfa-wg/">archives</a>). All feedback is welcome.</p><p>Publication as a Working Draft does not imply endorsement by the <acronym title="World Wide Web Consortium">W3C</acronym> 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 a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 <acronym title="World Wide Web Consortium">W3C</acronym> Patent Policy</a>. <acronym title="World Wide Web Consortium">W3C</acronym> maintains a <a href="http://www.w3.org/2004/01/pp-impl/44350/status" rel="disclosure">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 <acronym title="World Wide Web Consortium">W3C</acronym> Patent Policy</a>.</p></div><div id="toc" typeof="bibo:Chapter" about="#toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a href="#html-vs.-xhtml" class="tocxref"><span class="secno">1.1 </span>HTML vs. XHTML</a></li><li class="tocline"><a href="#validation" class="tocxref"><span class="secno">1.2 </span>Validation</a></li></ul></li><li class="tocline"><a href="#adding-machine-readable-hints-to-web-pages" class="tocxref"><span class="secno">2. </span>Adding Machine-Readable Hints to Web Pages</a><ul class="toc"><li class="tocline"><a href="#hints-on-social-networking-sites" class="tocxref"><span class="secno">2.1 </span>Hints on Social Networking Sites</a></li><li class="tocline"><a href="#indicating-title-in-the-text" class="tocxref"><span class="secno">2.2 </span>Indicating Title in the Text</a></li><li class="tocline"><a href="#links-with-flavor-1" class="tocxref"><span class="secno">2.3 </span>Links with Flavor</a></li><li class="tocline"><a href="#setting-a-default-vocabulary" class="tocxref"><span class="secno">2.4 </span>Setting a Default Vocabulary</a></li><li class="tocline"><a href="#multiple-items-per-page" class="tocxref"><span class="secno">2.5 </span>Multiple Items per Page</a></li></ul></li><li class="tocline"><a href="#going-deeper" class="tocxref"><span class="secno">3. </span>Going Deeper</a><ul class="toc"><li class="tocline"><a href="#contact-information" class="tocxref"><span class="secno">3.1 </span>Contact Information</a></li><li class="tocline"><a href="#describing-social-networks" class="tocxref"><span class="secno">3.2 </span>Describing Social Networks</a></li><li class="tocline"><a href="#internal-references" class="tocxref"><span class="secno">3.3 </span>Internal References</a></li><li class="tocline"><a href="#using-multiple-vocabularies" class="tocxref"><span class="secno">3.4 </span>Using Multiple Vocabularies</a><ul class="toc"><li class="tocline"><a href="#default-prefixes--initial-context" class="tocxref"><span class="secno">3.4.1 </span>Default Prefixes (Initial Context)</a></li></ul></li></ul></li><li class="tocline"><a href="#rdfa-tools" class="tocxref"><span class="secno">4. </span>RDFa Tools</a></li><li class="tocline"><a href="#some-more-advanced-rdfa-examples" class="tocxref"><span class="secno">5. </span>Some More Advanced RDFa Examples</a><ul class="toc"><li class="tocline"><a href="#importing-data" class="tocxref"><span class="secno">5.1 </span>Importing Data</a></li><li class="tocline"><a href="#automatic-summaries" class="tocxref"><span class="secno">5.2 </span>Automatic Summaries</a></li><li class="tocline"><a href="#address-visualization" class="tocxref"><span class="secno">5.3 </span>Address Visualization</a></li><li class="tocline"><a href="#linked-data-mashups" class="tocxref"><span class="secno">5.4 </span>Linked Data Mashups</a></li><li class="tocline"><a href="#enhanced-browser-interfaces" class="tocxref"><span class="secno">5.5 </span>Enhanced Browser Interfaces</a></li><li class="tocline"><a href="#publication-lists" class="tocxref"><span class="secno">5.6 </span>Publication lists</a></li></ul></li><li class="tocline"><a href="#you-said-something-about-rdf" class="tocxref"><span class="secno">6. </span>You Said Something about RDF?</a><ul class="toc"><li class="tocline"><a href="#custom-vocabularies" class="tocxref"><span class="secno">6.1 </span>Custom Vocabularies</a></li></ul></li><li class="tocline"><a href="#acknowledgments" class="tocxref"><span class="secno">7. </span>Acknowledgments</a></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">A. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">A.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">A.2 </span>Informative references</a></li></ul></li></ul></div>
    <div id="introduction" typeof="bibo:Chapter" about="#introduction" class="section">
      
<!-- OddPage -->
<h2><span class="secno">1. </span>Introduction</h2>
      <p> The web is a rich, distributed repository of interconnected
        information. Until recently, it was organized primarily for
        human consumption. On a typical web page, an HTML author might
        specify a headline, then a smaller sub-headline, a block of
        italicized text, a few paragraphs of average-size text, and,
        finally, a few single-word links. Web browsers will follow these
        presentation instructions faithfully. However, only the human
        mind understands what the headline expresses—a blog post title.
        The sub-headline indicates the author, the italicized text is
        the article's publication date, and the single-word links are
        subject categories. Computers do not understand the nuances
        between the information; the gap between what programs and
        humans understand is large. </p>
      <div style="margin: 0pt auto; text-align: center;" class="figure">
        <a class="figurelink" href="diagrams/presentation-vs-semantics.svg"><img src="diagrams/presentation-vs-semantics.png" alt="presentation vs. semantics" /></a>
        <p><a id="fig1"><em>Figure 1</em></a>: On the left, what
          browsers see. On the right, what humans see. Can we bridge the
          gap so that browsers see more of what we see?</p>
      </div>
      <p> What if the browser, or any machine consumer such as a Web
        crawler, received information on the meaning of a web page’s
        visual elements? A dinner party announced on a blog could be
        easily copied to the user’s calendar, an author’s complete
        contact information to the user’s address book. Users could
        automatically recall previously browsed articles according to
        categorization labels (i.e., tags). A photo copied and pasted
        from a web site to a school report would carry with it a link
        back to the photographer, giving him proper credit. A link
        shared by a user to his social network contacts would
        automatically carry additional data pulled from the original web
        page: a thumbnail, an author, and a specific title. When web
        data meant for humans is augmented with hints meant for computer
        programs, these programs become significantly more helpful,
        because they begin to understand the data’s structure. </p>
      <p> RDFa allows HTML authors to do just that. Using a few simple
        HTML attributes, authors can mark up human-readable data with
        machine-readable indicators for browsers and other programs to
        interpret. A web page can include markup for items as simple as
        the title of an article, or as complex as a user's complete
        social network. </p>
      <p> RDFa benefits from the power of RDF [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-PRIMER">RDF-PRIMER</a></cite>], the <acronym title="World Wide Web Consortium">W3C</acronym>’s
        standard for interoperable machine-readable data. However,
        readers of this document are not expected to understand RDF,
        only a basic level of HTML. </p>
      <div id="html-vs.-xhtml" typeof="bibo:Chapter" about="#html-vs.-xhtml" class="section">
        <h3><span class="secno">1.1 </span>HTML vs. XHTML</h3>
        <p> Historically, RDFa 1.0 [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-SYNTAX">RDFA-SYNTAX</a></cite>] was specified only
          for XHTML. RDFa 1.1 [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>] is the newest version and
          the one used in this document. RDFa 1.1 is specified for both
          XHTML [<cite><a class="bibref" rel="biblioentry" href="#bib-XHTML-RDFA">XHTML-RDFA</a></cite>] and HTML5 [<cite><a class="bibref" rel="biblioentry" href="#bib-HTML-RDFA">HTML-RDFA</a></cite>]. In fact, RDFa
          1.1 also works for any XML-based languages like SVG [<cite><a class="bibref" rel="biblioentry" href="#bib-SVG12">SVG12</a></cite>].
          This document uses HTML in all of the examples; for
          simplicity, we use the term “HTML” throughout this document to
          refer to all of the HTML-family languages. </p>
      </div>
      <div id="validation" typeof="bibo:Chapter" about="#validation" class="section">
        <h3><span class="secno">1.2 </span>Validation</h3>
        <p>RDFa is based on attributes. While some of the HTML
          attributes (e.g., <code>href</code>, <code>rel</code>) have
          been re-used, other RDFa 1.1 attributes are new. This is
          important because some of the (X)HTML validators may not
          properly validate the HTML code until they are updated to
          recognize the new RDFa 1.1 attributes. This is rarely a
          problem in practice since browsers simply ignore attributes
          that they do not recognize. None of the RDFa-specific
          attributes have any effect on the visual display of the HTML
          content. Authors do not have to worry about pages marked up
          with RDFa looking any different to a human being from pages
          not marked up with RDFa.</p>
      </div>
    </div>
    <div id="adding-machine-readable-hints-to-web-pages" typeof="bibo:Chapter" about="#adding-machine-readable-hints-to-web-pages" class="section">
      
<!-- OddPage -->
<h2><span class="secno">2. </span>Adding Machine-Readable Hints to Web Pages</h2>
      <p>Consider Alice, a blogger who publishes a mix of professional
        and personal articles at <code>http://example.com/alice</code>.
        We will construct markup examples to illustrate how Alice can
        use RDFa. The complete markup of these examples are available <a href="http://www.w3.org/2010/02/rdfa/sources/rdfa-primer/alice-example.html">on a dedicated page</a>. </p>
      <div id="hints-on-social-networking-sites" typeof="bibo:Chapter" about="#hints-on-social-networking-sites" class="section">
        <h3><span class="secno">2.1 </span>Hints on Social Networking Sites</h3>
        <p>Alice publishes a blog and would like to provide extra
          structural information on her pages like the publication date
          or the subject. She would like to use the terms defined in the
          Dublin Core vocabulary [<cite><a class="bibref" rel="biblioentry" href="#bib-DC11">DC11</a></cite>], a set of terms that are
          widely used by, for example, the publishing industry or
          libraries. She can do this easily by using RDFa:</p>
        <pre class="example">&lt;html&gt;
&lt;head&gt;
  &lt;title&gt;The Trouble with Bob&lt;/title&gt;
  &lt;meta <span class="hilite">property=&quot;http://purl.org/dc/terms/title&quot; content=&quot;The Trouble with Bob&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;http://purl.org/dc/terms/created&quot; content=&quot;2011-09-10&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;http://purl.org/dc/terms/subject&quot; content=&quot;photography&quot;</span> /&gt;
  ...
&lt;/head&gt;
...</pre>
        <p>(Notice the markup colored in red: these are the RDFa
          “hints”.)</p>
        <p> One useful way to visualize the structured data is: </p>
        <div style="margin: 0pt auto; text-align: center;" class="figure">
          <a class="figurelink" href="diagrams/title-and-author.svg"> <img src="diagrams/title-and-author.png" alt="relationship value is text" />
          </a>
          <p><a id="fig2"><em>Figure 2</em></a>: A visualization of the
            structured data for a blog post with a title of “The Trouble
            with Bob”, a creation date and a subject.</p>
        </div>
        <p> It is worth emphasizing that RDFa uses URLs to identify just about everything.
          This is why, instead of just using properties like <code>title</code>
          and <code>created</code>, we use <code>http://purl.org/dc/terms/title</code>
          and <code>http://purl.org/dc/terms/created</code>. The reason
          behind this design decision is rooted in data portability,
          consistency, and information sharing. Using URLs removes the
          possibility for ambiguities in terminology. Without ensuring
          that there is no ambiguity, the term “title” might mean “the
          title of a work”, “a job title”, or “the deed for real-estate
          property”. When each vocabulary term is a URL, a detailed
          explanation for the vocabulary term is just one click away. It
          allows anything, humans or machines, to follow the link to
          find out what a particular vocabulary term means. By using a
          URL to identify a particular type of title, for example <a href="http://purl.org/dc/terms/date">http://purl.org/dc/terms/created</a>,
          both humans and machines can understand that the URL
          unambiguously refers to the “Date of creation of the
          resource”, such as a web page.</p>
        <p> By using URLs as identifiers, RDFa provides a solid way of
          disambiguating vocabulary terms. It becomes trivial to
          determine whether or not vocabulary terms used in different
          documents mean the same thing. If the URLs are the same, the
          vocabulary terms mean the same thing. It also becomes very
          easy to create new vocabulary terms and vocabulary documents.
          If one can publish a document to the Web, one automatically
          has the power to create a new vocabulary document containing
          new vocabulary terms. </p>
      </div>
      <div id="indicating-title-in-the-text" typeof="bibo:Chapter" about="#indicating-title-in-the-text" class="section">
        <h3><span class="secno">2.2 </span>Indicating Title in the Text</h3>
        <p> As Alice adds her Dublin Core metadata, she notices that the
          title of her page is already in the visible markup: </p>
        <pre class="example">&lt;div&gt;
  &lt;h2&gt;The trouble with Bob&lt;/h2&gt;
  &lt;h3&gt;Alice&lt;/h3&gt;
  ...
&lt;/div&gt;</pre>
        <p> Alice can use the RDFa <code>property</code> attribute on
          the <code>h2</code> HTML element to indicate that this
          existing rendered text should also be machine-readable text
          indicating the page’s title: </p>
        <pre class="example">&lt;div&gt;
  &lt;h2 <span class="hilite">property=&quot;http://purl.org/dc/terms/title&quot;</span>&gt;The trouble with Bob&lt;/h2&gt;
  &lt;h3&gt;Alice&lt;/h3&gt;
  ...
&lt;/div&gt;</pre>
        <p> Note that in the example above, Alice did not need to use
          the <code>content</code> attribute, but could instead use the
          text that already existed in the document. The <code>property</code>
          attribute can be used on <em>any</em> element; by default, it
          takes the text content of that element except if the <code>content</code>
          attribute is present which then takes priority.</p>
      </div>
      <div id="links-with-flavor-1" typeof="bibo:Chapter" about="#links-with-flavor-1" class="section">
        <h3><span class="secno">2.3 </span><span id="links-with-flavor">Links with Flavor</span></h3>
        <p> The previous example demonstrated how Alice can markup text
          to make it machine readable. She would also like to mark up
          the links in a machine-readable way, to express the type of
          link being described. RDFa lets the publisher add a “flavor”
          to an existing clickable link that machine processors can
          understand. This makes the same markup help both humans and
          machines. </p>
        <p> In her blog’s footer, Alice already declares her content to
          be freely reusable, as long as she receives due credit when
          her articles are cited. The HTML includes a link to a Creative
          Commons [<cite><a class="bibref" rel="biblioentry" href="#bib-CC-ABOUT">CC-ABOUT</a></cite>] license: </p>
        <pre class="example">&lt;p&gt;All content on this site is licensed under
 &lt;a href=&quot;http://creativecommons.org/licenses/by/3.0/&quot;&gt;
     a Creative Commons License&lt;/a&gt;.&lt;/p&gt;</pre>
        <p> A human clearly understands this sentence, in particular the
          <em>meaning</em> of the link with respect to the current
          document: it indicates the document’s license, the conditions
          under which the page’s contents are distributed.
          Unfortunately, when Bob visits Alice’s blog, his browser sees
          only a plain link that could just as well point to one of
          Alice’s friends or to her CV. For Bob’s browser to understand
          that this link actually points to the document’s licensing
          terms, Alice needs to add some <em>flavor</em>, some
          indication of what <em>kind</em> of link this is. </p>
        <p> She can add this flavor using again the <code>property</code>
          attribute. Indeed, when the element contains the <code>href</code> attribute, 
          <code>property</code> is automatically associated with the value of this attribute
          rather than the textual content of the <code>a</code> element. The value of the
          attribute is the <code>http://creativecommons.org/ns#license</code>,
          defined by the Creative Commons: </p>
        <pre class="example">&lt;p&gt;All content on this site is licensed under
 &lt;a <span class="hilite">property=&quot;http://creativecommons.org/ns#license&quot;</span> href=&quot;http://creativecommons.org/licenses/by/3.0/&quot;&gt;
     a Creative Commons License&lt;/a&gt;.&lt;/p&gt;</pre>
        <p> With this small update, Bob’s browser will now understand
          that this link has a flavor: it indicates the blog’s license:
        </p>
        <div style="margin: 0pt auto; text-align: center;" class="figure">
          <a class="figurelink" href="diagrams/license.svg"> <img src="diagrams/license.png" alt="two Web pages connected by a link labeled 'license' and two notes with a 'license' relationship" />
          </a>
          <p><a id="fig3"><em>Figure 3</em></a>: A link with flavor: the
            link indicates the web page’s license. We can represent web
            pages as nodes, the link as an arrow connecting those nodes,
            and the link’s flavor as the label on that arrow.</p>
        </div>
        <p> Alice is quite pleased that she was able to add only
          structured-data hints via RDFa, never having to repeat the
          content of her text or the URL of her clickable links. </p>
      </div>
      <div id="setting-a-default-vocabulary" typeof="bibo:Chapter" about="#setting-a-default-vocabulary" class="section">
        <h3><span class="secno">2.4 </span>Setting a Default Vocabulary</h3>
        <p> In a number of simple use cases, such as our example with
          Alice’s blog, HTML authors will predominantly use a single
          vocabulary. On the other hand, while generating full URLs via
          a CMS system is not a particular problem, typing these by hand
          may be error prone and tedious for humans. To alleviate this
          problem RDFa introduces the <code>vocab</code> attribute to
          let the author declare a single vocabulary for a chunk of
          HTML. Thus, instead of:</p>
        <pre class="example">&lt;html&gt;
&lt;head&gt;
  &lt;title&gt;The Trouble with Bob&lt;/title&gt;
  &lt;meta <span class="hilite">property=&quot;http://purl.org/dc/terms/title&quot; content=&quot;The Trouble with Bob&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;http://purl.org/dc/terms/created&quot; content=&quot;2011-09-10&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;http://purl.org/dc/terms/subject&quot; content=&quot;photography&quot;</span> /&gt;
  ...
&lt;/head&gt;
...</pre>
        <p> Alice can write: </p>
        <pre class="example">&lt;html <span class="hilite">vocab=&quot;http://purl.org/dc/terms/&quot;</span>&gt;
&lt;head&gt;
  &lt;title&gt;The Trouble with Bob&lt;/title&gt;
  &lt;meta <span class="hilite">property=&quot;title&quot; content=&quot;The Trouble with Bob&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;created&quot; content=&quot;2011-09-10&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;subject&quot; content=&quot;photography&quot;</span> /&gt;
  ...
&lt;/head&gt;
...</pre>
        <p> Note how the property values are single “terms” now; these
          are simply concatenated to the URL defined via the <code>vocab</code>
          attribute. The attribute can be placed on any HTML element
          (i.e., not only on the <code>html</code> element like in the
          example) and its effect is valid for all the elements below
          that point. </p>
        <p>Default vocabularies and full URIs can be mixed at any time.
          I.e., Alice could have written:</p>
        <pre class="example">&lt;html <span class="hilite">vocab=&quot;http://purl.org/dc/terms/&quot;</span>&gt;
&lt;head&gt;
  &lt;title&gt;The Trouble with Bob&lt;/title&gt;
  &lt;meta <span class="hilite">property=&quot;title&quot; content=&quot;The Trouble with Bob&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;created&quot; content=&quot;2011-09-10&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;http://purl.org/dc/terms/subject&quot; content=&quot;photography&quot;</span> /&gt;
  ...
&lt;/head&gt;
...</pre>
        <p>Perhaps a more interesting example is the combination of the
          header with the licensing segment of her web page:</p>
        <pre class="example">&lt;html <span class="hilite">vocab=&quot;http://purl.org/dc/terms/&quot;</span>&gt;
&lt;head&gt;
  &lt;title&gt;The Trouble with Bob&lt;/title&gt;
  &lt;meta <span class="hilite">property=&quot;title&quot; content=&quot;The Trouble with Bob&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;created&quot; content=&quot;2011-09-10&quot;</span> /&gt;
  &lt;meta <span class="hilite">property=&quot;subject&quot; content=&quot;photography&quot;</span> /&gt;
  ...
&lt;/head&gt;
&lt;body&gt;
...
 &lt;p&gt;All content on this site is licensed under
 &lt;a <span class="hilite">property=&quot;http://creativecommons.org/ns#license&quot;</span> href=&quot;http://creativecommons.org/licenses/by/3.0/&quot;&gt;
     a Creative Commons License&lt;/a&gt;.&lt;/p&gt;
&lt;/body&gt;
&lt;/html&gt;</pre>
        <p>The full URL for the license term is necessary to avoid
          mixing vocabularies. Of course, Alice could have also written:</p>
        <pre class="example">&lt;html <span class="hilite">vocab=&quot;http://purl.org/dc/terms/&quot;</span>&gt;
&lt;head&gt;
   &lt;title&gt;The Trouble with Bob&lt;/title&gt;
   &lt;meta <span class="hilite">property=&quot;title&quot; content=&quot;The Trouble with Bob&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;created&quot; content=&quot;2011-09-10&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;subject&quot; content=&quot;photography&quot;</span> /&gt;
   ...
 &lt;/head&gt;
 &lt;body&gt;
...
  &lt;p <span class="hilite">vocab=&quot;http://creativecommons.org/ns#&quot;</span>&gt;All content on this site is licensed under
    &lt;a <span class="hilite">property=&quot;license&quot;</span> href=&quot;http://creativecommons.org/licenses/by/3.0/&quot;&gt;
      a Creative Commons License&lt;/a&gt;.&lt;/p&gt;
 &lt;/body&gt;
 &lt;/html&gt;</pre>
        <p>because the <code>vocab</code> in the license paragraph
          overrides the definition inherited from the top of the
          document.</p>
      </div>
      <div id="multiple-items-per-page" typeof="bibo:Chapter" about="#multiple-items-per-page" class="section">
        <h3><span class="secno">2.5 </span>Multiple Items per Page</h3>
        <p> Alice’s blog contains, of course, multiple entries.
          Sometimes, Alice’s sister Eve guest blogs, too. The front page
          of the blog lists the 10 most recent entries, each with its
          own title, author, and introductory paragraph. How, then,
          should Alice mark up the title of each of these entries
          individually even though they all appear within the same web
          page? RDFa provides <code>about</code>, an attribute for
          specifying the exact URL to which the contained RDFa markup
          applies: </p>
        <pre class="example">&lt;div <span class="hilite">vocab=&quot;http://purl.org/dc/terms/&quot;</span>&gt;
			
   &lt;div <span class="hilite">about=&quot;/alice/posts/trouble_with_bob&quot;</span>&gt;
      &lt;h2 <span class="hilite">property=&quot;title&quot;</span>&gt;The trouble with Bob&lt;/h2&gt;
      &lt;h3 <span class="hilite">property=&quot;creator&quot;</span>&gt;Alice&lt;/h3&gt;
      ...
   &lt;/div&gt;
 
   &lt;div <span class="hilite">about=&quot;/alice/posts/jos_barbecue&quot;</span>&gt;
      &lt;h2 <span class="hilite">property=&quot;title&quot;</span>&gt;Jo's Barbecue&lt;/h2&gt;
      &lt;h3 <span class="hilite">property=&quot;creator&quot;</span>&gt;Eve&lt;/h3&gt;
      ...
   &lt;/div&gt;
 
   ...
 
&lt;/div&gt;        </pre>
        <p>(Note that we used relative URLs in the example; the value of
          <code>about</code> could have been <em>any</em> URLs,
          relative or absolute.) We can represent this, once again, as a
          diagram connecting URLs to properties: </p>
        <div style="margin: 0pt auto; text-align: center;" class="figure">
          <a href="diagrams/multiple-blog-entries.svg" class="figurelink">
            <img src="diagrams/multiple-blog-entries.png" alt="two separate nodes, each with two properties" />
          </a>
          <p><a id="fig4"><em>Figure 4</em></a>: Multiple Items per
            Page: each blog entry is represented by its own node, with
            properties attached to each. </p>
        </div>
        <p> Alice can use the same technique to give her friend Bob
          proper credit when she posts one of his photos: </p>
        <pre class="example">&lt;div <span class="hilite">about=&quot;/alice/posts/trouble_with_bob&quot;</span>&gt;
    &lt;h2 <span class="hilite">property=&quot;title&quot;</span>&gt;The trouble with Bob&lt;/h2&gt;
      
    The trouble with Bob is that he takes much better photos than I do:
	
    &lt;div <span class="hilite">about=&quot;http://example.com/bob/photos/sunset.jpg&quot;</span>&gt;
      &lt;img src=&quot;http://example.com/bob/photos/sunset.jpg&quot; /&gt;
      &lt;span <span class="hilite">property=&quot;title&quot;</span>&gt;Beautiful Sunset&lt;/span&gt;
      by &lt;span <span class="hilite">property=&quot;creator&quot;</span>&gt;Bob&lt;/span&gt;.
    &lt;/div&gt;
 &lt;/div&gt;       </pre>
        <p> Notice how the innermost <code>about</code> value, <code>http://example.com/bob/photos/sunset.jpg</code>,
          “overrides” the outer value <code>/alice/posts/trouble_with_bob</code>
          for all markup inside the innermost <code>div</code>. And,
          once again, here is a diagram that abstractly represents the
          underlying data of this new portion of markup: </p>
        <div style="margin: 0pt auto; text-align: center;" class="figure">
          <a href="diagrams/image-about.svg" class="figurelink"> <img src="diagrams/image-about.png" alt="two separate nodes, each with two properties" /> </a>
          <p><a id="fig5"><em>Figure 5</em></a>: Describing a Photo</p>
        </div>
      </div>
    </div>
    <div id="going-deeper" typeof="bibo:Chapter" about="#going-deeper" class="section">
      
<!-- OddPage -->
<h2><span class="secno">3. </span>Going Deeper</h2>
      <div id="contact-information" typeof="bibo:Chapter" about="#contact-information" class="section">
        <h3><span class="secno">3.1 </span>Contact Information</h3>
        <p> Alice would also like to make information about herself,
          such as her email address, phone number, and other details,
          easily available to her friends’ contact management software.
          This time, instead of describing the properties of a web page,
          she’s going to describe the properties of a person: herself.
          To do this, she adds deeper structure, so that she can connect
          multiple items that themselves have properties. </p>
        <p> Alice already has contact information displayed on her blog.
        </p>
        <pre class="example">&lt;span&gt;
     Alice Birpemswick, 
     Email: &lt;a href=&quot;mailto:alice@example.com&quot;&gt;alice@example.com&lt;/a&gt;,
     Phone: &lt;a href=&quot;tel:+1-617-555-7332&quot;&gt;+1 617.555.7332&lt;/a&gt;
&lt;/span&gt;</pre>
        <p> The Dublin Core vocabulary does not provide property names
          for describing contact information, but the Friend-of-a-Friend
          [<cite><a class="bibref" rel="biblioentry" href="#bib-FOAF">FOAF</a></cite>] vocabulary does. Alice decides to use the FOAF
          vocabulary and declares a FOAF “Person”. For this purpose,
          Alice uses <code>typeof</code>, an RDFa attribute that is
          specifically meant to declare a new data item with a certain
          type: </p>
        <pre class="example">&lt;span <span class="hilite">typeof=&quot;http://xmlns.com/foaf/0.1/Person&quot;</span>&gt;
  ...</pre>
        <p> Alice realizes that she only intends to use the FOAF
          vocabulary at this point, so she uses the <code>vocab</code>
          attribute to further simplify her markup (and overriding the
          effects of any <code>vocab</code> attributes that may have
          been used in, for example, the <code>html</code> element at
          the top). </p>
        <pre class="example">&lt;span <span class="hilite">vocab=&quot;http://xmlns.com/foaf/0.1/&quot; typeof=&quot;Person&quot;</span>&gt;
  ...</pre>
        <p> Then, Alice indicates which content on the page represents
          her full name, email address, and phone number: </p>
        <pre class="example">&lt;span <span class="hilite">vocab=&quot;http://xmlns.com/foaf/0.1/&quot; typeof=&quot;Person&quot;</span>&gt;
   &lt;span <span class="hilite">property=&quot;name&quot;</span>&gt;Alice Birpemswick&lt;/span&gt;,
  Email: &lt;a <span class="hilite">property=&quot;mbox&quot;</span> href=&quot;mailto:alice@example.com&quot;&gt;alice@example.com&lt;/a&gt;,
  Phone: &lt;a <span class="hilite">property=&quot;phone&quot;</span> href=&quot;tel:+1-617-555-7332&quot;&gt;+1 617.555.7332&lt;/a&gt;
&lt;/span&gt;</pre>
        <p> Note how Alice did not specify <code>about</code> like she
          did when adding blog entry metadata. If she is not declaring
          what she is talking about, how does the RDFa Processor know
          what she’s identifying? In RDFa, in the absence of an <code>about</code> attribute, the <code>typeof</code>
          attribute on the enclosing <code>div</code> implicitly sets
          the subject of the properties marked up within that <code>div</code>.
          That is, the name, email address, and phone number are
          associated with a new node of type <code>Person</code>. This
          node has no URL to identify it, so it is called a <em>blank
            node</em> as shown on the figure: </p>
        <div style="margin: 0pt auto; text-align: center;" class="figure">
          <a href="diagrams/contact-info.svg" class="figurelink"> <img src="diagrams/contact-info.png" alt="single 'blank' node with 4 properties" />
          </a>
          <p><a id="fig6"><em>Figure 6</em></a>: A Blank Node: blank
            nodes are not identified by URL. Instead, many of them have
            an RDFa <code>typeof</code> attribute that identifies the
            type of data they represent. <br />
            (We’ve used a short-hands to label the arrows, in order to
            save space and clarify the diagram. The actual labels are
            always the full URLs.)</p>
        </div>
        <p>Of course, Alice could also decide to use a real URI for
          herself instead of a blank node. Adding an <code>about</code>
          attribute would do just that:</p>
        <pre class="example">&lt;span <span class="hilite">vocab=&quot;http://xmlns.com/foaf/0.1/&quot; about=&quot;#me&quot; typeof=&quot;Person&quot;</span>&gt;
   &lt;span <span class="hilite">property=&quot;name&quot;</span>&gt;Alice Birpemswick&lt;/span&gt;,
     Email: &lt;a <span class="hilite">property=&quot;mbox&quot;</span> href=&quot;mailto:alice@example.com&quot;&gt;alice@example.com&lt;/a&gt;,
     Phone: &lt;a <span class="hilite">property=&quot;phone&quot;</span> href=&quot;tel:+1-617-555-7332&quot;&gt;+1 617.555.7332&lt;/a&gt;
&lt;/span&gt;</pre>
        <p>It is considered as a good practice to use real URIs whenever possible, i.e., Alice’s second alternative
        should be preferred. If a real URI is used, then it becomes possible to unambigously refer to that particular
        node, whereas that becomes much more complicated with blank nodes.</p>
        
        <p class="note">The <code>about=&quot;#me&quot;</code> markup is a FOAF
          convention: the URL that represents the <em>person</em> Alice
          is <code>http://example.com/alice#me</code>. It should not be
          confused with Alice’s homepage, <code>http://example.com/alice</code>.
        </p>
      </div>     
      <div id="describing-social-networks" typeof="bibo:Chapter" about="#describing-social-networks" class="section">
        <h3><span class="secno">3.2 </span>Describing Social Networks</h3>
        <p> Alice continues to mark up her page by adding information
          about her friends, including at least their names and
          homepages. She starts with plain old HTML: </p>
        <pre class="example">&lt;div&gt;
   &lt;ul&gt;
      &lt;li&gt;
        &lt;a href=&quot;http://example.com/bob/&quot;&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li&gt;
        &lt;a href=&quot;http://example.com/eve/&quot;&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li&gt;
        &lt;a href=&quot;http://example.com/manu/&quot;&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;</pre>
        <p>First, Alice indicates that the friends she is describing are
          people, as opposed to animals or imaginary friends, by using
          the type <code>Person</code> in <code>typeof</code>
          attributes. </p>
        <pre class="example">&lt;div <span class="hilite">vocab=&quot;http://xmlns.com/foaf/0.1/&quot;</span>&gt;
   &lt;ul&gt;
      &lt;li <span class="hilite">typeof=&quot;Person&quot;</span>&gt;
        &lt;a href=&quot;http://example.com/bob/&quot;&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="hilite">typeof=&quot;Person&quot;</span>&gt;
        &lt;a href=&quot;http://example.com/eve/&quot;&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="hilite">typeof=&quot;Person&quot;</span>&gt;
        &lt;a href=&quot;http://example.com/manu/&quot;&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;        </pre>
        <p>Beyond declaring the type of data we are dealing with, each <code>typeof</code>
          creates a new blank node with its own distinct properties, all
          without having to provide URL identifiers. Thus, Alice can
          easily indicate each friend’s homepage: </p>
        <pre class="example">&lt;div vocab=&quot;http://xmlns.com/foaf/0.1/&quot;&gt;
   &lt;ul&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a <span class="hilite">property=&quot;homepage&quot;</span> href=&quot;http://example.com/bob/&quot;&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a <span class="hilite">property=&quot;homepage&quot;</span> href=&quot;http://example.com/eve/&quot;&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a <span class="hilite">property=&quot;homepage&quot;</span> href=&quot;http://example.com/manu/&quot;&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;       </pre>
        <p>Alice would also like to improve the markup by expressing each person’s name using
        RDFa, too. However, the <code>property</code> attribute cannot be used for this purpose; indeed,
        <code>property</code> is automatically associated with <code>href</code> in this case. Instead,
        Alice can use the <code>rel</code> attribute. This attribute will pick up the value of
        <code>href</code> and, in the presence of <code>rel</code>, <code>property</code> will
        use the textual content of the element instead. I.e., Alice can write:</p>
         <pre class="example">&lt;div vocab=&quot;http://xmlns.com/foaf/0.1/&quot;&gt;
   &lt;ul&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a <span class="hilite">rel=&quot;homepage&quot;</span> href=&quot;http://example.com/bob/&quot; <span class="hilite">property=&quot;name&quot;</span>&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a <span class="hilite">rel=&quot;homepage&quot;</span> href=&quot;http://example.com/eve/&quot; <span class="hilite">property=&quot;name&quot;</span>&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a <span class="hilite">rel=&quot;homepage&quot;</span> href=&quot;http://example.com/manu/&quot; <span class="hilite">property=&quot;name&quot;</span>&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;       </pre>
        <p> Using <code>property</code>, Alice has specified that the
          linked text (“Bob”, “Eve”, and “Manu”) are her friends’ names; with <code>rel</code>;
          with <code>rel</code>, she indicates that the clickable links
          are her friends’ homepages. She could not have used <code>rel</code>
          to be associated with the linked text; this attribute can be used
          <em>exclusively</em> with links like the one in the <code>href</code> attribute.
        </p>
        <p>Note that <code>rel</code> can be used at any time, not only in association with <code>property</code>.
          It can also be used <em>instead of</em> <code>property</code> when used with <code>href</code>; i.e.,
          the example above, without the linked texts, could have been written as:
        </p>
         <pre class="example">&lt;div vocab=&quot;http://xmlns.com/foaf/0.1/&quot;&gt;
   &lt;ul&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a <span class="hilite">rel=&quot;homepage&quot;</span> href=&quot;http://example.com/bob/&quot;&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a <span class="hilite">rel=&quot;homepage&quot;</span> href=&quot;http://example.com/eve/&quot;&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a <span class="hilite">rel=&quot;homepage&quot;</span> href=&quot;http://example.com/manu/&quot;&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;       </pre>

          <p>Alice is happy that, with so
          little additional markup, she’s able to fully express both a
          pleasant human-readable page and a machine-readable dataset. </p>
        <p> Alice is a member of 5 different social networking sites.
          She is tired of repeatedly entering information about her
          friends in each new social networking site, so she decides to
          list her friends in one place—on her website. With RDFa, she
          can indicate her friendships on her own web page and let
          social networking sites read it automatically. So far, Alice
          has listed three individuals but has not specified her
          relationship with them; they might be her friends, or they
          might be her favorite 17th century poets. To indicate that she
          knows them, she uses the FOAF property <code>foaf:knows</code>:
        </p>
        <pre class="example">&lt;div vocab=&quot;http://xmlns.com/foaf/0.1/&quot; <span class="hilite">about=&quot;#me&quot;</span> &gt;
   &lt;ul&gt;
      &lt;li <span class="hilite">property=&quot;knows&quot;</span> typeof=&quot;Person&quot;&gt;
        &lt;a rel=&quot;homepage&quot; href=&quot;http://example.com/bob&quot; property=&quot;name&quot;&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="hilite">property=&quot;knows&quot;</span> typeof=&quot;Person&quot;&gt;
        &lt;a rel=&quot;homepage&quot; href=&quot;http://example.com/eve&quot; property=&quot;name&quot;&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="hilite">property=&quot;knows&quot;</span> typeof=&quot;Person&quot;&gt;
        &lt;a rel=&quot;homepage&quot; href=&quot;http://example.com/manu&quot; property=&quot;name&quot;&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;       </pre>
        <p>With this, Alice could describe here social network:</p>
         <div style="margin: 0pt auto; text-align: center;" class="figure">
          <a href="diagrams/social-network.svg" class="figurelink"> <img src="diagrams/social-network.png" alt="8 node network with 12 relationships" />
          </a>
          <p><a id="fig7"><em>Figure 7</em></a>: Alice’s social network</p>
        </div>
         <p>Note that Alice had to repeat the <code>property=&quot;knows&quot;</code>. When there are only a few persons in her
         social network, that may be fine, but it might become error prone in some other cases: she may forget to
         add that attribute. An alternative is to use the <code>rel</code> attribute instead. In most of the
         cases <code>rel</code> has a similar behavior to <code>property</code>, but it also has the concept of
         <em>chaining</em> that can be used as follows:</p>
        <pre class="example">&lt;div vocab=&quot;http://xmlns.com/foaf/0.1/&quot; about=&quot;#me&quot; <span class="hilite">rel=&quot;knows&quot;</span>&gt;
   &lt;ul&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a rel=&quot;homepage&quot; href=&quot;http://example.com/bob&quot; property=&quot;name&quot;&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a rel=&quot;homepage&quot; href=&quot;http://example.com/eve&quot; property=&quot;name&quot;&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li typeof=&quot;Person&quot;&gt;
        &lt;a rel=&quot;homepage&quot; href=&quot;http://example.com/manu&quot; property=&quot;name&quot;&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;       </pre>
         <p>Using <code>rel=&quot;knows&quot;</code> <em>once</em> at the
          top-most <code>div</code> is enough to connect Bob, Eve, and
          Manu to Alice. This is achieved thanks 
          <em>chaining</em>: because the top-level <code>rel</code> is
          without a corresponding <code>href</code>, it connects to any
          contained node. In this case the three nodes defined by <code>typeof</code>.
        </p>
      </div>
      <div id="internal-references" typeof="bibo:Chapter" about="#internal-references" class="section">
        <h3><span class="secno">3.3 </span>Internal References</h3>
        <p>Alice may want to add her personal data to her individual
          blog items, too. She decides to combine her FOAF data with the
          blog items, i.e.:</p>
        <pre class="example">&lt;div vocab=&quot;http://purl.org/dc/terms/&quot;&gt;
			
   &lt;div about=&quot;/alice/posts/trouble_with_bob&quot;&gt;
      &lt;h2 property=&quot;title&quot;&gt;The trouble with Bob&lt;/h2&gt;
      &lt;h3 <span class="hilite">rel=&quot;creator&quot;</span>&gt;
        &lt;span vocab=&quot;http://xmlns.com/foaf/0.1/&quot; <span class="hilite">about=&quot;#me&quot;</span> typeof=&quot;Person&quot;&gt;
          &lt;span property=&quot;name&quot;&gt;Alice Birpemswick&lt;/span&gt;,
          Email: &lt;a rel=&quot;mbox&quot; href=&quot;mailto:alice@example.com&quot;&gt;alice@example.com&lt;/a&gt;,
          Phone: &lt;a rel=&quot;phone&quot; href=&quot;tel:+1-617-555-7332&quot;&gt;+1 617.555.7332&lt;/a&gt;
        &lt;/span&gt;
      &lt;/h3&gt;
      ...
   &lt;/div&gt;
   ...
&lt;/div&gt;        </pre>
        <p>Note the usage of the <code>rel</code> attribute instead of
          <code>property</code> for the Dublin Core <code>creator</code>
          term; this is because the data now involves more than just a
          simple text. The structured data she generates looks like
          this:</p>
        <div style="margin: 0pt auto; text-align: center;" class="figure">
          <a href="diagrams/blog-with-foaf.svg" class="figurelink"> <img src="diagrams/blog-with-foaf.png" alt="The simple blog structure extended with Alice's foaf data" />
          </a>
          <p><a id="fig8"><em>Figure 8</em></a>: Alice’s blog item with
            data about herself.</p>
        </div>
        <p>Unfortunately, this solution is not optimal. Indeed, Alice
          would like to design her Web page so that her personal data
          would not appear on the page in each individual blog item but,
          rather, in one place like a footnote or a sidebar. What she
          would like to see is something like:</p>
        <div style="margin: 0pt auto; text-align: center;" class="figure">
          <img src="diagrams/blog-screenshot.jpg" alt="Mock-up of Alice's blog page design, with blogs on the left and personal data on the right" />
          <p><a id="fig9"><em>Figure 9</em></a>: Structure of Alice’s
            Site: individual blog items on the left, personal data, linked from the blog using RDFa terms, in a
            sidebar.</p>
        </div>
        <p>If the FOAF data is included into each blog item, Alice would
          have to create a complex set of CSS rules to achieve the
          visual effect she wants. Instead, Alice decides to use another
          RDFa attribute, namely <code>resource</code>:</p>
        <pre class="example">&lt;div vocab=&quot;http://purl.org/dc/terms/&quot;&gt;
   &lt;div about=&quot;/alice/posts/trouble_with_bob&quot;&gt;
      &lt;h2 property=&quot;title&quot;&gt;The trouble with Bob&lt;/h2&gt;
      &lt;h3 <span class="hilite">rel=&quot;creator&quot; resource=&quot;#me&quot;</span>&gt;Alice&lt;/h3&gt;
      ...
   &lt;/div&gt;
&lt;/div&gt;
   ...
&lt;div class=&quot;sidebar&quot;&gt;
   ...
  &lt;span vocab=&quot;http://xmlns.com/foaf/0.1/&quot; <span class="hilite">about=&quot;#me&quot;</span> typeof=&quot;Person&quot;&gt;
    &lt;span property=&quot;name&quot;&gt;Alice Birpemswick&lt;/span&gt;,
    Email: &lt;a rel=&quot;mbox&quot; href=&quot;mailto:alice@example.com&quot;&gt;alice@example.com&lt;/a&gt;,
    Phone: &lt;a rel=&quot;phone&quot; href=&quot;tel:+1-617-555-7332&quot;&gt;+1 617.555.7332&lt;/a&gt;
  &lt;/span&gt;
&lt;/div&gt;        </pre>
        <p>The <code>resource</code> attribute plays exactly the same role as <code>href</code>
          but does not provide a clickable link to the browser like <code>href</code>
          does. Also, <code>resource</code> can be used on <em>any</em>
          HTML element, in contrast to <code>href</code>. In this case,
          usage of this attribute allows Alice to “distribute” the
          various parts of the structured data on her page, although the
          data itself is identical to the one on the previous example,
          shown on <a href="#fig8">Figure 8</a>.</p>
      </div>
      <div id="using-multiple-vocabularies" typeof="bibo:Chapter" about="#using-multiple-vocabularies" class="section">
        <h3><span class="secno">3.4 </span>Using Multiple Vocabularies</h3>
        <p>The previous examples show that, for more complex cases,
          multiple vocabularies have to be used to express the various
          aspects of structured data. We have seen Alice using the
          Dublin Core, as well as the FOAF and the Creative Commons
          vocabularies, but there may be more. For example:</p>
        <ul>
          <li>She plans to install a plugin into her blog software so
            that her social networking site’s “Like” button appears at
            the bottom of each of her posts. In order to give her social
            networking site information about her blog posts’ title,
            thumbnail, and content type, she may want to use the Open
            Graph Protocol [<cite><a class="bibref" rel="biblioentry" href="#bib-OGP">OGP</a></cite>] vocabulary to mark up her content.</li>
          <li>She may want to add more information on her blog, to make
            use of <a href="http://rdfs.org/sioc/applications/">specialized
              engines</a> that can process the SIOC
            (Semantically-Interlinked Online Communities) vocabulary
            [<cite><a class="bibref" rel="biblioentry" href="#bib-SIOC">SIOC</a></cite>], a vocabulary that has been developed for the
            Social Web.
          </li>
        </ul>
        <p>Of course, Alice can use either full URLs for all the terms,
          or can use the <code>vocab</code> attribute to abbreviate the
          terms for the predominant vocabulary. But, in some cases, the
          vocabularies cannot be separated easily, which means that <code>vocab</code>
          may not solve all the problems. Here is, for example, the type
          of HTML she might end up with:</p>
        <pre class="example">&lt;html <span class="hilite">vocab=&quot;http://purl.org/dc/terms/&quot;</span>&gt;
&lt;head&gt;
   &lt;title&gt;The Trouble with Bob&lt;/title&gt;
   &lt;meta <span class="hilite">property=&quot;http://ogp.me/ns#title&quot; content=&quot;The Trouble with Bob&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;http://ogp.me/ns#type&quot; content=&quot;text&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;http://ogp.me/ns#image&quot; content=&quot;http://example.com/alice/bob-ugly.jpg&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;subject&quot; content=&quot;photography&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;created&quot; content=&quot;2011-09-10&quot;</span> /&gt;
   ...
 &lt;/head&gt;
 &lt;body&gt;
   &lt;div <span class="hilite">typeof=&quot;http://rdfs.org/sioc/ns#Post&quot;</span>&gt;
      &lt;h2 <span class="hilite">property=&quot;title&quot;</span>&gt;The trouble with Bob&lt;/h2&gt;
      &lt;h3 <span class="hilite">property=&quot;creator&quot;</span>&gt;Alice&lt;/h3&gt;
      &lt;p <span class="hilite">property=&quot;http://rdfs.org/sioc/ns#content&quot;</span>&gt;The trouble with Bob is that he takes much better photos than I do:&lt;/p&gt;
      ...
   &lt;/div&gt;
...
  &lt;/body&gt;
 &lt;/html&gt;</pre>
        <p>Note that the SIOC and the Dublin Core terms are intertwined
          for a specific blog, and it becomes an arbitrary choice to use
          <code>vocab</code> for <code>http://purl.org/dc/terms/</code>
          or for <code>http://rdfs.org/sioc/ns#</code>. The same holds
          for the header, which contains both Dublin Core and Open Graph
          Protocol terms.</p>
        <p>To alleviate this problem, RDFa offers the possibility of using <em>prefixed</em>
          terms: a special <code>prefix</code> attribute can assign
          prefixes to represent URLs and, using those prefixes, the
          vocabulary elements themselves can be abbreviated. The <code>prefix:reference</code>
          syntax is used: the URL associated with <code>prefix</code>
          is simply concatenated to <code>reference</code> to create a
          full URL. Here is how the HTML of the previous example looks
          like when prefixes are used:</p>
        <pre class="example">&lt;html <span class="hilite">prefix=&quot;dc: http://purl.org/dc/terms/ sioc: http://rdfs.org/sioc/ns# og: http://ogp.me/ns#&quot; </span>&gt;
&lt;head&gt;
   &lt;title&gt;The Trouble with Bob&lt;/title&gt;
   &lt;meta <span class="hilite">property=&quot;og:title&quot; content=&quot;The Trouble with Bob&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;og:type&quot; content=&quot;text&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;og:image&quot; content=&quot;http://example.com/alice/bob-ugly.jpg&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;dc:subject&quot; content=&quot;photography&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;dc:created&quot; content=&quot;2011-09-10&quot;</span> /&gt;
   ...
 &lt;/head&gt;
 &lt;body&gt;
   &lt;div <span class="hilite">typeof=&quot;sioc:Post&quot;</span>&gt;
      &lt;h2 <span class="hilite">property=&quot;dc:title&quot;</span>&gt;The trouble with Bob&lt;/h2&gt;
      &lt;h3 <span class="hilite">property=&quot;dc:creator&quot;</span>&gt;Alice&lt;/h3&gt;
      &lt;p <span class="hilite">property=&quot;sioc:content&quot;</span>&gt;The trouble with Bob is that he takes much better photos than I do:&lt;/p&gt;
      ...
   &lt;/div&gt;
 &lt;/body&gt;
 &lt;/html&gt;</pre>
        <p>The usage of prefixes can greatly reduce possible errors by
          concentrating the vocabulary choices to one place in the code.
          Just like <code>vocab</code>, the <code>prefix</code>
          attribute can appear anywhere in the HTML file, only affecting
          the elements below. <code>prefix</code> and <code>vocab</code> can also be mixed, for example:</p>
        
        <pre class="example">&lt;html <span class="hilite">vocab=&quot;http://purl.org/dc/terms/&quot;</span> <span class="hilite">prefix=&quot;sioc: http://rdfs.org/sioc/ns# og: http://ogp.me/ns#&quot; </span>&gt;
&lt;head&gt;
   &lt;title&gt;The Trouble with Bob&lt;/title&gt;
   &lt;meta <span class="hilite">property=&quot;og:title&quot; content=&quot;The Trouble with Bob&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;og:type&quot; content=&quot;text&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;og:image&quot; content=&quot;http://example.com/alice/bob-ugly.jpg&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;subject&quot; content=&quot;photography&quot;</span> /&gt;
   &lt;meta <span class="hilite">property=&quot;created&quot; content=&quot;2011-09-10&quot;</span> /&gt;
   ...
 &lt;/head&gt;
 &lt;body&gt;
   &lt;div <span class="hilite">typeof=&quot;sioc:Post&quot;</span>&gt;
      &lt;h2 <span class="hilite">property=&quot;dc:title&quot;</span>&gt;The trouble with Bob&lt;/h2&gt;
      &lt;h3 <span class="hilite">property=&quot;creator&quot;</span>&gt;Alice&lt;/h3&gt;
      &lt;p <span class="hilite">property=&quot;sioc:content&quot;</span>&gt;The trouble with Bob is that he takes much better photos than I do:&lt;/p&gt;
      ...
   &lt;/div&gt;
 &lt;/body&gt;
 &lt;/html&gt;</pre>
        <div class="note"> An important issue may arise if the <code>html</code>
          element contains a large number of prefix declarations. The
          character encoding (i.e., UTF-8, UTF-16, ascii, etc.) used for an HTML5 file is declared using a meta
          element in the header. In HTML5 this meta declaration must
          fall within the first 512 bytes of the page, or the HTML5
          processor (browser, parser, etc.) will try to detect the
          encoding some using heuristics. A very “long” <code>html</code>
          tag may therefore lead to problems. One way of avoiding the
          issue is to place most of the prefix declarations on the <code>body</code>
          element.</div>
        <div id="default-prefixes--initial-context" typeof="bibo:Chapter" about="#default-prefixes--initial-context" class="section">
          <h4><span class="secno">3.4.1 </span><span id="default-profiles">Default Prefixes (Initial Context)</span></h4>
          <p>A number of vocabularies
            are very widely used by the Web community with well-known prefixes—the Dublin Core
            vocabulary is a good example. These common vocabularies tend
            to be defined over and over again, and sometimes Web page
            authors forget to declare them altogether.</p>
          <p>To alleviate this issue, RDFa 1.1 has the concept of an <em>initial
              context</em> that defined a set of default prefixes.
            These prefixes, whose list is maintained and regularly updated (i.e., new prefixes added) by the <acronym title="World Wide Web Consortium">W3C</acronym>,
            provide a number of pre-defined prefixes that are known to
            the RDFa processor. Prefix declarations in a document always
            override declarations made through the defaults, but if a
            web page author forgets to declare a common vocabulary such
            as Dublin Core or FOAF, the RDFa Processor will fall back to
            those. The list of default prefixes are, of course,
          <a href="http://www.w3.org/2011/rdfa-context/rdfa-1.1">available on the Web</a> for everyone to read.</p>
           <p>For example, the following example does <em>not</em>
            declare the <code>dc:</code> prefix using a <code>prefix</code>
            attribute:</p>
          <pre class="example">&lt;html&gt;
 &lt;head&gt;
   &lt;meta <span class="hilite">property=&quot;dc:title&quot;</span> content=&quot;The trouble with Bob&quot; /&gt;
   &lt;meta <span class="hilite">property=&quot;dc:created&quot;</span> content=&quot;2011-09-10&quot; /&gt;
   ...
 &lt;/head
   ...
&lt;/html&gt;</pre>
          <p>However, an RDFa processor still recognizes the <code>dc:title</code>
            and <code>dc:creator</code> short-hands and expands the
            values to the corresponding URLs. The RDFa processor is able
            to do this because the <code>dc</code> prefix is part of
            the default prefixes in the initial
            <a href="http://www.w3.org/2011/rdfa-context/rdfa-1.1"><code>http://www.w3.org/2011/rdfa-context/rdfa-1.1</code></a>
            context.</p>
          <p class="note">Default prefixes are used as a mechanism to
            correct RDFa documents where authors accidentally forgot to
            declare common prefixes. While authors may rely on these
            to be available for RDFa 1.1 documents, the
            prefixes may change over the course of 5-10 years, although
            the policy of <acronym title="World Wide Web Consortium">W3C</acronym> is that once a prefix is defined as part
            of a default profile, that particular prefix will <em>not</em>
            be changed or removed. Nevertheless, the best way to ensure
            that the prefixes that document authors use always map to
            the intent of the author is to use the <code>prefix</code>
            attribute to declare these prefixes. </p>
          <p>Since default prefixes are meant to be a last-resort
            mechanism to help novice document authors, the markup above
            is not recommended. The rest of this document will utilize
            authoring best practices by declaring all prefixes in order
            to make the document author’s intentions explicit.</p>
        </div>
      </div>
    </div>
    <div id="rdfa-tools" typeof="bibo:Chapter" about="#rdfa-tools" class="section">
      
<!-- OddPage -->
<h2><span class="secno">4. </span>RDFa Tools</h2>
      <p>There is a wide variety of tools that can be used to generate
        or process RDFa data. Good sources for these are the <a href="http://www.w3.org/2001/sw/wiki/RDFa">RDFa
          page of the <acronym title="World Wide Web Consortium">W3C</acronym> Semantic Web Wiki</a>, or the <a href="http://rdfa.info/rdfa-implementations/">RDFa
         Wiki’s implementation page</a>. The RDFa Wiki also contains
        further examples and information on how to get involved.</p>
    </div>
    <div id="some-more-advanced-rdfa-examples" typeof="bibo:Chapter" about="#some-more-advanced-rdfa-examples" class="section">
      
<!-- OddPage -->
<h2><span class="secno">5. </span>Some More Advanced RDFa Examples</h2>
      <p>This section contains a set of more advanced RDFa examples.
        They are provided to help the reader understand a few more RDFa
        usage patterns. Many of these examples describe not only how to
        encode data into RDF but also what an application might try to
        do with the data. Note that the implementation of those examples
        may require programmatic access to the RDFa content.</p>
      <div id="importing-data" typeof="bibo:Chapter" about="#importing-data" class="section">
        <h3><span class="secno">5.1 </span>Importing Data</h3>
        <p> Amy has enriched her band’s web-site to include event
          information. Google Rich Snippets are used to mark up
          information for search engines to use when displaying enhanced
          search results. Amy also uses some JavaScript code that automatically extracts the event
          information from a page and adds an entry into a personal
          calendar. </p>
        <p> Brian finds Amy’s web-site through Google and opens the
          band’s page. He decides that he wants to go to the next
          concert. Brian is able to add the details to his calendar by
          clicking on the link that is automatically generated by the
          JavaScript tool. The JavaScript extracts the RDFa from the web
          page using, and places the event into
          Brian's personal calendaring software—Google Calendar. Amy
          automatically extracts
          the event information from a page and adds an entry into
          her personal calendar using some JavaScript code.
        </p>
        <pre class="example">&lt;div <span class="hilite">vocab=&quot;http://rdf.data-vocabulary.org/#&quot;</span> <span class="hilite">typeof=&quot;Event&quot;</span>&gt; 
  &lt;a <span class="hilite">rel=&quot;url&quot;</span> <span class="hilite">href=&quot;http://amyandtheredfoxies.example.com/events&quot;</span> 
     <span class="hilite">property=&quot;summary&quot;</span>&gt;Tour Info: Amy And The Red Foxies&lt;/a&gt;
  &lt;span <span class="hilite">property=&quot;location&quot;</span> <span class="hilite">typeof=&quot;Organization&quot;</span>&gt;
    &lt;a <span class="hilite">property=&quot;url&quot;</span> <span class="hilite">href=&quot;http://www.kammgarn.de/&quot;</span>&gt;&lt;span <span class="hilite">property=&quot;name&quot;</span>&gt;Kammgarn&lt;/span&gt;&lt;/a&gt;
  &lt;/span&gt;
  &lt;div&gt;&lt;img <span class="hilite">property=&quot;photo&quot;</span> <span class="hilite">src=&quot;foxies.jpg&quot;</span>/&gt;&lt;/div&gt;
  &lt;span <span class="hilite">property=&quot;summary&quot;</span>&gt;Hey K-Town, Amy And The Red Foxies will rock Kammgarn in October.&lt;/span&gt;
  When: 
  &lt;span <span class="hilite">property=&quot;startDate&quot;</span> <span class="hilite">content=&quot;2009-10-15T19:00&quot;</span>&gt;15. Oct., 7:00 pm&lt;/span&gt;-
  &lt;span <span class="hilite">property=&quot;endDate&quot;</span> <span class="hilite">content=&quot;2009-10-15T21:00&quot;</span>&gt;9:00 pm&lt;/span&gt;
  Category: &lt;span <span class="hilite">property=&quot;eventType&quot;</span>&gt;concert&lt;/span&gt;
&lt;/div&gt;</pre>
        <p>Note that this example also uses the <code>src</code>
          attribute; just <code>href</code> is recognized by RDFa, so
          is <code>src</code>. The example relates, via a link with
          “flavor” to the image whose URL is <code>foxies.jpg</code>. Note also that, when using <code>rel</code> and <code>property</code>
        on the same element, <code>property</code> is used to generate a literal object, whereas the <code>rel</code> is used to add
        the “flavor” to the link. Finally, the example makes use of the fact that <code>property</code> (or <code>rel</code>),
        when used with <code>typeof</code>, creates a blank node that becomes the subject for the statements in the subtree.</p>
      </div>
      <div id="automatic-summaries" typeof="bibo:Chapter" about="#automatic-summaries" class="section">
        <h3><span class="secno">5.2 </span>Automatic Summaries</h3>
        <p> Mary is responsible for keeping the projects section of her
          company’s home page up-to-date. She wants to display
          info-boxes that summarize details about the members associated
          with each project. The information should appear when hovering
          the mouse over the link to each member's homepage. Since each
          member’s homepage is annotated with RDFa, Mary writes a script
          that requests the page’s content and extracts necessary
          information via the RDFa API. </p>
        <p>To use unique identification for the different interest
          areas, Mary decides to use URLs rather than simple text. She
          chooses to use the terms defined by <a href="http://dbpedia.org">DBpedia</a>.
          DBPedia is a dump of Wikipedia data that is expressed as a
          vocabulary. It is widely used on the Semantic Web for
          identifying concepts in the human world. The usage of the <code>resource</code>
          allows her to add a reference to the human readable version of
          the interest page on Wikipedia. Indeed, since both the <code>resource</code>
          and the <code>href</code> attributes may appear on the same
          element, the former takes precedence in RDFa while the latter
          can be used to re-direct the person viewing the page to a
          human-readable form of the DBPedia entry. Finally Mary uses
          an RDFa script to extract this kind of information
          from the HTML source in order to populate the infoboxes.</p>
        <pre class="example">&lt;div <span class="hilite">prefix=&quot;dc: http://purl.org/dc/terms/ foaf: http://xmlns.com/foaf/0.1/&quot;</span>
     <span class="hilite">about=&quot;#me&quot;</span> <span class="hilite">typeof=&quot;foaf:Person&quot;</span>&gt;
  &lt;span <span class="hilite">property=&quot;foaf:name&quot;</span> <span class="hilite">content=&quot;Bob&quot;</span>&gt;My&lt;/span&gt; interests are:
  &lt;ol <span class="hilite">about=&quot;#me&quot;</span> <span class="hilite">typeof=&quot;foaf:Person&quot;</span> <span class="hilite">rel=&quot;foaf:interest&quot;</span>&gt;
    &lt;li&gt;&lt;a <span class="hilite">resource=&quot;http://dbpedia.org/resource/Semantic_Web&quot;</span>
           href=&quot;http://en.wikipedia.org/wiki/Semantic_Web&quot;&gt;
            &lt;span <span class="hilite">property=&quot;dc:title&quot;</span>&gt;Semantic Web&lt;/span&gt;
        &lt;/a&gt;
    &lt;/li&gt;
    &lt;li&gt;&lt;a <span class="hilite">resource=&quot;http://dbpedia.org/resource/Facebook&quot;</span>
           href=&quot;http://en.wikipedia.org/wiki/Facebook&quot;&gt;
           &lt;span <span class="hilite">property=&quot;dc:title&quot;</span>&gt;Facebook&lt;/span&gt;
        &lt;/a&gt;
    &lt;/li&gt;
    &lt;li&gt;&lt;a <span class="hilite">resource=&quot;http://dbpedia.org/resource/Twitter&quot;</span>
           href=&quot;http://en.wikipedia.org/wiki/Twitter&quot;&gt;
           &lt;span <span class="hilite">property=&quot;dc:title&quot;</span>&gt;Twitter&lt;/span&gt;
        &lt;/a&gt;
    &lt;/li&gt;     
  &lt;/ol&gt;      
&lt;/div&gt;</pre>
      <p>Mary also uses the chaining, via the <code>rel</code> attribute, to avoid repeating that attribute on
      all the entry on her interests and to set the right subject for the textual explanation of those.</p>
      </div>
      <div id="address-visualization" typeof="bibo:Chapter" about="#address-visualization" class="section">
        <h3><span class="secno">5.3 </span>Address Visualization</h3>
        <p> Richard has created a site that lists his favorite
          restaurants and their locations. He doesn’t want to generate
          code specific to the various mapping services on the Web.
          Instead of creating specific markup for Yahoo Maps, Google
          Maps, MapQuest, and Google Earth, he instead adds address
          information via RDFa to each restaurant entry. This enables
          him to build a general tool that extracts the address
          information and access the mapping tool the user wishes. </p>
        <pre class="example">&lt;div <span class="hilite">vocab=&quot;http://www.w3.org/2006/vcard/ns#&quot;</span> <span class="hilite">typeof=&quot;VCard&quot;</span>&gt;
  &lt;span <span class="hilite">property=&quot;fn&quot;</span>&gt;Wong Kei&lt;/span&gt;
  &lt;span <span class="hilite">property=&quot;street-address&quot;</span>&gt;41-43 Wardour Street&lt;/span&gt;
  &lt;span <span class="hilite">property=&quot;locality&quot;</span>&gt;London&lt;/span&gt;, &lt;span property=&quot;country-name&quot;&gt;United Kingdom&lt;/span&gt;
  &lt;span <span class="hilite">property=&quot;tel&quot;</span>&gt;020 74373071&lt;/span&gt;
&lt;/div&gt;</pre>
      </div>
      <div id="linked-data-mashups" typeof="bibo:Chapter" about="#linked-data-mashups" class="section">
        <h3><span class="secno">5.4 </span>Linked Data Mashups</h3>
        <p> Marie is a chemist, researching the effects of ethanol on
          the spatial orientation of animals. She writes about her
          research on her blog and often makes references to chemical
          compounds. She would like any reference to these compounds to
          automatically have a picture of the compound's structure shown
          as a tooltip, and a link to the compound’s entry on the
          National Center for Biotechnology Information [NCBI] Web site.
          Similarly, she would like visitors to be able to visualize the
          chemical compound in the page using a new HTML5 canvas widget
          she has found on the web that combines data from different
          chemistry websites. </p>
        <pre class="example">&lt;div <span class="hilite">vocab=&quot;http://rdf.freebase.com/rdf/&quot;</span>&gt;
   My latest study about the effects of 
   &lt;span <span class="hilite">about=&quot;en.ethanol&quot;</span> 
      <span class="hilite">typeof=&quot;http://dbpedia.org/ontology/ChemicalCompound&quot;</span> 
      <span class="hilite">property=&quot;chemistry.chemical_compound.pubchem_id&quot;</span> 
      <span class="hilite">content=&quot;702&quot;</span>&gt;ethanol&lt;/span&gt; on mice's spatial orientation show that ...
&lt;/div&gt;</pre>
        
<!--  http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=702  -->

      </div>
      <div id="enhanced-browser-interfaces" typeof="bibo:Chapter" about="#enhanced-browser-interfaces" class="section">
        <h3><span class="secno">5.5 </span>Enhanced Browser Interfaces</h3>
        <p> Dave is writing a browser plugin that filters product offers
          in a web page and displays an icon to buy the product or save
          it to a public wishlist. The plugin searches for any mention
          of product names, thumbnails, and offered prices. The
          information is listed in the URL bar as an icon, and upon
          clicking the icon, displayed in a sidebar in the browser. He
          can then add each item to a list that is managed by the
          browser plugin and published on a wishlist website. </p>
        <p>Because many of his pages make use of the Good Relation
          ontology [<cite><a class="bibref" rel="biblioentry" href="#bib-GR">GR</a></cite>], which is widely used to markup products, Dave
          decides to make use of the <code>vocab</code> facility of
          RDFa to simplify his code. He also forgets to declare the <code>rdfs</code>
          prefix, but since it is defined by the RDFa default profile,
          the data that he intended to express using the <code>rdfs</code>
          prefix will still be extracted by all conforming RDFa
          processors.</p>
        <pre class="example">&lt;div <span class="hilite">prefix=&quot;foaf: http://xmlns.com/foaf/0.1/&quot;</span>&gt;
 
  &lt;div <span class="hilite">vocab=&quot;http://purl.org/goodrelations/v1#&quot;</span> <span class="hilite">about=&quot;#offering&quot;</span> <span class="hilite">typeof=&quot;Offering&quot;</span>&gt;
    &lt;div <span class="hilite">property=&quot;foaf:page&quot;</span> <span class="hilite">resource=&quot;http://www.amazon.com/Harry-Potter-Deathly-Hallows-Book/dp/0545139708&quot;</span>&gt;&lt;/div&gt;
    &lt;div <span class="hilite">property=&quot;rdfs:label&quot;</span>&gt;Harry Potter and the Deathly Hallows&lt;/div&gt;
    &lt;div <span class="hilite">property=&quot;rdfs:comment&quot;</span>&gt;In this final, seventh installment of the Harry Potter series, J.K. Rowling 
    unveils in spectactular fashion the answers to the many questions that have been so eagerly 
    awaited. The spellbinding, richly woven narrative, which plunges, twists and turns at a 
    breathtaking pace, confirms the author as a mistress of storytelling, whose books will be read, 
    reread and read again.&lt;/div&gt;
    &lt;div&gt;
       &lt;img <span class="hilite">property=&quot;foaf:depiction&quot;</span> src=&quot;http://ecx.images-amazon.com/images/I/51ynI7I-qnL._SL500_AA300_.jpg&quot; /&gt;
    &lt;/div&gt;
    &lt;div <span class="hilite">property=&quot;hasBusinessFunction&quot;</span> <span class="hilite">resource=http://purl.org/goodrelations/v1#Sell&quot;</span>&gt;&lt;/div&gt;
    &lt;div <span class="hilite">property=&quot;hasPriceSpecification&quot; typeof=&quot;UnitPriceSpecification&quot;</span>&gt;Buy for
      &lt;span <span class="hilite">property=&quot;hasCurrency&quot;</span> <span class="hilite">content=&quot;USD&quot;</span>&gt;$&lt;/span&gt;
      &lt;span <span class="hilite">property=&quot;hasCurrencyValue&quot;</span>&gt;7.49&lt;/span&gt;
    &lt;/div&gt; Pay via: 
      &lt;span <span class="hilite">property=&quot;acceptedPaymentMethods&quot;</span> <span class="hilite">resource=&quot;http://purl.org/goodrelations/v1#PayPal&quot;</span>&gt;PayPal&lt;/span&gt;
      &lt;span <span class="hilite">property=&quot;acceptedPaymentMethods&quot;</span> <span class="hilite">resource=&quot;http://purl.org/goodrelations/v1#MasterCard&quot;</span>&gt;MasterCard&lt;/span&gt;
    &lt;/div&gt;
  &lt;/div&gt;
   
&lt;/div&gt;</pre>
      </div>
      <div id="publication-lists" typeof="bibo:Chapter" about="#publication-lists" class="section">
        <h3><span class="secno">5.6 </span>Publication lists</h3>
        <p>Mark wants to publish his publication list, which contains references to articles, books, book chapters, etc.
        He can use the Bibliographic Ontology [<cite><a class="bibref" rel="biblioentry" href="#bib-BIBO">BIBO</a></cite>] for that purpose. However, the problem he has is that many of his
        publications have co-authors and, in the publication world, the <em>order</em> of the authors in a citation is
        important. </p>
        <p>Mark can use the <code>inlist</code> feature of RDFa. Using this feature guarantees that the order of the
        resources, as they appear in the HTML text, is preserved in terms of structured data, too:</p>
        
  <pre class="example">&lt;p prefix=&quot;bibo: http://purl.org/ontology/bibo/ dc: http://purl.org/dc/terms/ typeof=&quot;bibo:Chapter&quot;&gt;
  “&lt;span property=&quot;dc:title&quot;&gt;Semantic Annotation and Retrieval&lt;/span&gt;”, by
  &lt;span <span class="hilite">inlist</span> property=&quot;dc:creator&quot;&gt;Ben Adida&lt;/span&gt;,
  &lt;span <span class="hilite">inlist</span> property=&quot;dc:creator&quot;&gt;Mark Birbeck&lt;/span&gt;, and
  &lt;span <span class="hilite">inlist</span> property=&quot;dc:creator&quot;&gt;Ivan Herman&lt;/span&gt;.
&lt;/p&gt;</pre>
    </div>
    </div>
     <div id="you-said-something-about-rdf" typeof="bibo:Chapter" about="#you-said-something-about-rdf" class="section">
      
<!-- OddPage -->
<h2><span class="secno">6. </span>You Said Something about RDF?</h2>
      <p> RDF, the Resource Description Framework, is the abstract data
        representation we have drawn out as graphs in the examples
        above. Each arrow in the graph is represented as a
        subject-property-object triple: the subject is the node at the
        start of the arrow, the property is the arrow itself, and the
        object is the node or literal at the end of the arrow. A set of
        such RDF triples is often called an “RDF graph”, and is
        typically stored in what is often called a “Triple Store” or a
        “Graph Store”. </p>
      <p> Consider the first example graph: </p>
      <div style="margin: 0pt auto; text-align: center;" class="figure">
        <a href="diagrams/title-and-author.svg" class="figurelink"> <img src="diagrams/title-and-author.png" alt="relationship value is text" />
        </a> </div>
      <p> The three RDF triples for this graph are written, using the
        Turtle syntax [<cite><a class="bibref" rel="biblioentry" href="#bib-TURTLE">TURTLE</a></cite>], as follows: </p>
      <pre class="example">&lt;http://www.example.com/alice/posts/trouble_with_bob&gt;
    &lt;http://purl.org/dc/terms/title&gt; &quot;The Trouble with Bob&quot; ;
    &lt;http://purl.org/dc/terms/subject&gt; &quot;photography&quot; ;
    &lt;http://purl.org/dc/terms/created&gt; &quot;2011-09-10&quot; .</pre>
      <p> Also, the <strong>TYPE</strong> arrows we drew are no
        different from other arrows. The <strong>TYPE</strong> is just
        another property that happens to be a core RDF property, namely
        <code>rdf:type</code>. The <code>rdf</code> vocabulary is
        located at <code>http://www.w3.org/1999/02/22-rdf-syntax-ns</code>.
        The contact information example from above should thus be
        diagrammed as: </p>
      <div style="margin: 0pt auto; text-align: center;" class="figure">
        <a href="diagrams/type.svg" class="figurelink"> <img src="diagrams/type.png" alt="blank node with rdf:type foaf:Person" /> </a> </div>
      <p> The point of RDF is to provide a universal language for
        expressing data. A unit of data can have any number of
        properties that are expressed as URLs. These URLs can be reused
        by any publisher, much like any web publisher can link to any
        web page, even ones they did not create themselves. Given data,
        in the form of RDF triples, collected from various locations,
        and using the RDF query language SPARQL [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SPARQL-QUERY">RDF-SPARQL-QUERY</a></cite>],
        one can search for “friends of Alice’s who created items whose
        title contains the word ‘Bob’,” whether those items are blog
        posts, videos, calendar events, or other data types. </p>
      <p> RDF is an abstract data model meant to maximize the reuse of
        vocabularies. RDFa is a way to express RDF data within HTML, in
        a way that is machine-readable, and by reusing the existing
        human-readable data in the document. </p>
      <div id="custom-vocabularies" typeof="bibo:Chapter" about="#custom-vocabularies" class="section">
        <h3><span class="secno">6.1 </span>Custom Vocabularies</h3>
        <p> As Alice marks up her page with RDFa, she may discover the
          need to express data, such as her favorite photos, that is not
          covered by existing vocabularies. If she needs to, Alice can
          create a custom vocabulary suited for her needs. Once a
          vocabulary is created, it can be used in RDFa markup like any
          other vocabulary. </p>
        <p> The instructions on how to create a vocabulary, also known
          as an RDF Schema, are available in Section 5 of the RDF Primer
          [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SCHEMA">RDF-SCHEMA</a></cite>]. At a high level, the creation of a vocabulary
          for RDFa involves: </p>
        <ol>
          <li>Selecting a URL where the vocabulary will reside, for
            example: <code>http://example.com/photos/vocab#</code>.</li>
          <li>Publishing the vocabulary document at the specified
            vocabulary URL. The vocabulary document defines the classes
            and properties that make up the vocabulary. For example,
            Alice may want to define the classes <code>Photo</code> and
            <code>Camera</code>, as well as the property <code>takenWith</code>
            that relates a photo to the camera with which it was taken.</li>
          <li>Using the vocabulary in an HTML document either with the <code>vocab</code>
            attribute or with the prefix declaration mechanism. For
            example: <code>prefix=&quot;photo:
              http://example.com/photos/vocab#&quot;</code> and <code>typeof=&quot;photo:Camera&quot;</code>.</li>
        </ol>
        <p> It is worth noting that anyone who can publish a document on
          the Web can publish a vocabulary and thus define new data
          fields they may wish to express. RDF and RDFa allow fully
          distributed extensibility of vocabularies. </p>
      </div>
    </div>

    <div id="acknowledgments" typeof="bibo:Chapter" about="#acknowledgments" class="section">
      
<!-- OddPage -->
<h2><span class="secno">7. </span>Acknowledgments</h2>
      <p>At the time of publication, the active members of the RDF Web
        Application Working Group were:</p>
      <ul>
        <li>Ben Adida, Creative Commons</li>
        <li>Benjamin Adrian, German Research Center for Artificial
          Intelligence (DFKI) GmbH</li>
        <li>Mark Birbeck, webBackplane.com (Invited Expert)</li>
        <li>Markus Gylling, DAISY Consortium</li>
        <li>Stéphane Corlosquet, Massachusetts General Hospital</li>
        <li>Jean-Pierre Evain, European Broadcasting Union</li>
        <li>Ivan Herman, <acronym title="World Wide Web Consortium">W3C</acronym></li>
        <li>Toby Inkster (Invited Expert)</li>
        <li>Gregg Kellogg (Invited Expert)</li>
        <li>Niklas Linström (Invited Expert)
        </li>
        <li>Shane McCarron, Applied Testing and Technology, Inc.
          (Invited Expert)</li>
        <li>Knud Möller, DERI Galway at the National University of
          Ireland and Talis Group Ltd.</li>
        <li>John O'Donovan, British Broadcasting Corporation</li>
        <li>Steven Pemberton, Centre for Mathematics and Computer
          Science (CWI)</li>
        <li>Nathan Rixham (Invited Expert)</li>
        <li>Thomas Steiner, Google, Inc.</li>
        <li>Ted Thibodeau, OpenLink Software</li>
        <li>Robert Weir, IBM Corporation</li>
      </ul>
    </div>
  

<div id="references" class="appendix section" typeof="bibo:Chapter" about="#references">
<!-- OddPage -->
<h2><span class="secno">A. </span>References</h2><div id="normative-references" typeof="bibo:Chapter" about="#normative-references" class="section"><h3><span class="secno">A.1 </span>Normative references</h3><p>No normative references.</p></div><div id="informative-references" typeof="bibo:Chapter" about="#informative-references" class="section"><h3><span class="secno">A.2 </span>Informative references</h3><dl class="bibliography" about=""><dt id="bib-BIBO">[BIBO]</dt><dd rel="dcterms:references">Frédérick Giasson and Bruce D'Arcus; <a href="http://bibliontology.com/"><cite>The Bibliographic Ontology</cite></a>. URL: <a href="http://bibliontology.com/">http://bibliontology.com/</a>
</dd><dt id="bib-CC-ABOUT">[CC-ABOUT]</dt><dd rel="dcterms:references"><a href="http://creativecommons.org/about/licenses/"><cite>Creative Commons: About Licenses</cite></a> URL: http://creativecommons.org/about/licenses/ 
</dd><dt id="bib-DC11">[DC11]</dt><dd rel="dcterms:references">Dublin Core metadata initiative. <a href="http://dublincore.org/documents/dcmi-terms/"><cite>Dublin Core metadata element set, version 1.1.</cite></a> July 1999. Dublin Core recommendation. URL: <a href="http://dublincore.org/documents/dcmi-terms/">http://dublincore.org/documents/dcmi-terms/</a>
</dd><dt id="bib-FOAF">[FOAF]</dt><dd rel="dcterms:references">Dan Brickley, Libby Miller. <a href="http://xmlns.com/foaf/spec/"><cite>FOAF Vocabulary Specification 0.98.</cite></a> 9 August 2010. URL: <a href="http://xmlns.com/foaf/spec/">http://xmlns.com/foaf/spec/</a>
</dd><dt id="bib-GR">[GR]</dt><dd rel="dcterms:references">Martin Hepp; <a href="http://purl.org/goodrelations/v1"><cite>GoodRelations Language Reference</cite></a>. URL: <a href="http://purl.org/goodrelations/v1">http://purl.org/goodrelations/v1</a>
</dd><dt id="bib-HTML-RDFA">[HTML-RDFA]</dt><dd rel="dcterms:references">Manu Sporny; et al. <a href="http://www.w3.org/TR/rdfa-in-html/"><cite>HTML+RDFa</cite></a> 25 May 2011. W3C Working Draft. URL: <a href="http://www.w3.org/TR/rdfa-in-html/">http://www.w3.org/TR/rdfa-in-html/</a> 
</dd><dt id="bib-OGP">[OGP]</dt><dd rel="dcterms:references"><a href="http://ogp.me"> <cite>The Open Graph Protocol</cite></a>.  December 2010. URL: <a href="http://ogp.me">http://ogp.me</a>
</dd><dt id="bib-RDF-PRIMER">[RDF-PRIMER]</dt><dd rel="dcterms:references">Frank Manola; Eric Miller. <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/"><cite>RDF Primer.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/">http://www.w3.org/TR/2004/REC-rdf-primer-20040210/</a> 
</dd><dt id="bib-RDF-SCHEMA">[RDF-SCHEMA]</dt><dd rel="dcterms:references">Dan Brickley; Ramanathan V. Guha. <a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210"><cite>RDF Vocabulary Description Language 1.0: RDF Schema.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210">http://www.w3.org/TR/2004/REC-rdf-schema-20040210</a> 
</dd><dt id="bib-RDF-SPARQL-QUERY">[RDF-SPARQL-QUERY]</dt><dd rel="dcterms:references">Andy Seaborne; Eric Prud'hommeaux. <a href="http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115"><cite>SPARQL Query Language for RDF.</cite></a> 15 January 2008. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115">http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115</a> 
</dd><dt id="bib-RDFA-CORE">[RDFA-CORE]</dt><dd rel="dcterms:references">Shane McCarron; et al. <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331"><cite>RDFa Core 1.1: Syntax and processing rules for embedding RDF through attributes.</cite></a> 31 March 2011. W3C Working Draft. URL: <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331">http://www.w3.org/TR/2011/WD-rdfa-core-20110331</a> 
</dd><dt id="bib-RDFA-SYNTAX">[RDFA-SYNTAX]</dt><dd rel="dcterms:references">Ben Adida, et al. <a href="http://www.w3.org/TR/2008/REC-rdfa-syntax-20081014"><cite>RDFa in XHTML: Syntax and Processing.</cite></a> 14 October 2008. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2008/REC-rdfa-syntax-20081014">http://www.w3.org/TR/2008/REC-rdfa-syntax-20081014</a> 
</dd><dt id="bib-SIOC">[SIOC]</dt><dd rel="dcterms:references">Uldis Bojārs and John G. Breslin; <a href="http://www.w3.org/Submission/2007/SUBM-sioc-spec-20070612/"><cite>SIOC Core Ontology Specification</cite></a>. W3C Member Submission. URL: <a href="http://www.w3.org/Submission/2007/SUBM-sioc-spec-20070612/">http://www.w3.org/Submission/2007/SUBM-sioc-spec-20070612/</a>
</dd><dt id="bib-SVG12">[SVG12]</dt><dd rel="dcterms:references">Craig Northway; Dean Jackson. <a href="http://www.w3.org/TR/2005/WD-SVG12-20050413"><cite>Scalable Vector Graphics (SVG) Full 1.2 Specification.</cite></a> 13 April 2005. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2005/WD-SVG12-20050413">http://www.w3.org/TR/2005/WD-SVG12-20050413</a> 
</dd><dt id="bib-TURTLE">[TURTLE]</dt><dd rel="dcterms:references">David Beckett, Tim Berners-Lee. <a href="http://www.w3.org/TeamSubmission/turtle/"><cite>Turtle: Terse RDF Triple Language.</cite></a> January 2008. W3C Team Submission. URL: <a href="http://www.w3.org/TeamSubmission/turtle/">http://www.w3.org/TeamSubmission/turtle/</a> 
</dd><dt id="bib-XHTML-RDFA">[XHTML-RDFA]</dt><dd rel="dcterms:references">Shane McCarron; et. al. <a href="http://www.w3.org/TR/2011/WD-xhtml-rdfa-20110331"><cite>XHTML+RDFa 1.1.</cite></a> 31 March 2011. W3C Working Draft. URL: <a href="http://www.w3.org/TR/2011/WD-xhtml-rdfa-20110331">http://www.w3.org/TR/2011/WD-xhtml-rdfa-20110331</a> 
</dd></dl></div></div></body></html>