mod-metaAttributes.html 22.4 KB

Raw Blame History Permalink

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html lang="en" xml:lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta name="generator" content="HTML Tidy, see www.w3.org" />
<title>XHTML 2.0 - XHTML Metainformation Attributes Module</title>
<link rel="start" type="text/html" href="Overview.html" />
<link rel="contents" type="text/html" href="Overview.html#toc" />
<link rel="prev" type="text/html" href="mod-meta.html" />
<link rel="next" type="text/html" href="mod-object.html" />
<link rel="stylesheet" type="text/css" href="xhtml.css" />
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-WD.css" />
</head>
<body>
<div class="navbar">[<a accesskey="P" href="mod-meta.html">previous</a>] &#160; [<a accesskey="N" href="mod-object.html">next</a>] &#160;[<a accesskey="T" href="Overview.html#toc">table of
contents</a>] &#160;[<a accesskey="E" href="elements.html">elements</a>] &#160;[<a accesskey="A" href="attributes.html">attributes</a>]

<hr />
</div>

<h1><a id="s_metaAttributesmodule" name="s_metaAttributesmodule">24.</a> XHTML Metainformation Attributes Module</h1>

<div class='subtoc'>
<p><strong>Contents</strong></p>

<ul class='toc'>
<li class='tocline'>24.1. <a href="#col_Metainformation" class="tocxref">Metadata Attribute Collection</a></li>

<li class='tocline'>24.2. <a href="#sec_24.2." class="tocxref">Meta and RDF</a></li>

<li class='tocline'>24.3. <a href="#sec_24.3." class="tocxref">Metadata as Content</a></li>

<li class='tocline'>24.4. <a href="#sec_24.4." class="tocxref">Mapping Lexical Content</a></li>
</ul>
</div>

<p>This section is <em>normative</em>.</p>

<p>The Metainformation Attributes Module defines the <a class="csref" href="mod-metaAttributes.html#col_Metainformation">Metainformation</a> attribute collection. This collection allows elements to
be annotated with metadata throughout an XHTML-family document.</p>

<h2><a id="col_Metainformation" name="col_Metainformation">24.1.</a> Metadata Attribute Collection</h2>

<!-- INCLUDING ATTRIBUTE modules/attributes/about.mhtml -->
<dl class='attrDef'>
<dt><a class="adef" id="adef_metaAttributes_about"><span class="adef">about</span></a> = <span class="datatype"><a href="abstraction.html#dt_URI">URI</a></span></dt>

<dd>This attribute specifies which resource has a specified property.

<p>If this attribute is not present then the resource being referred to by a <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_property">property</a> attribute on the same element is
decided as follows:</p>

<ol>
<li>If the element on which the other metadata attributes are attached is a child of a <a class="eref" href="mod-meta.html#edef_meta_link">link</a> then the metadata inferred by the element concerns
the URI referred to in the <a class="eref" href="mod-meta.html#edef_meta_link">link</a>.</li>

<li>Otherwise, the metadata inferred by the element concerns the current document.</li>
</ol>

<div class="example">
<p>Example</p>

<pre>
&lt;meta about="http://www.example.com/" property="dc:created"&gt;2004-03-20&lt;/meta&gt;
</pre>
</div>
</dd>
</dl>

<!-- END OF ATTRIBUTE FILE modules/attributes/about.mhtml --><!-- INCLUDING ATTRIBUTE modules/attributes/content.mhtml -->
<dl class='attrDef'>
<dt><a class="adef" id="adef_metaAttributes_content"><span class="adef">content</span></a> = <span class="datatype"><a href="abstraction.html#dt_CDATA">CDATA</a></span></dt>

<dd>This attribute specifies the metadata associated with an element. If not specified, then the metadata for an element is its content.

<div class="example">
<p>Example</p>

<pre>
&lt;meta about="http://www.example.com/" property="dc:created" content="2004-03-20"/&gt;
</pre>
</div>
</dd>
</dl>

<!-- END OF ATTRIBUTE FILE modules/attributes/content.mhtml --><!-- INCLUDING ATTRIBUTE modules/attributes/datatype.mhtml -->
<dl class='attrDef'>
<dt><a class="adef" id="adef_metaAttributes_datatype"><span class="adef">datatype</span></a> = <span class="datatype"><a href="abstraction.html#dt_QName">QName</a></span></dt>

<dd>This attribute defines the datatype of the content metadata of the element. If the attribute is not specified, then the default value is <a class="xsdref" href=
"http://www.w3.org/TR/xmlschema-2/#string">string</a> as defined by [<a class="nref" href="references.html#ref_XMLSCHEMA">XMLSCHEMA</a>].

<div class="example">
<p>Example</p>

<pre>
&lt;meta about="http://www.example.com/" property="dc:created" datatype="xsd:date"&gt;2004-03-20&lt;/meta&gt;
</pre>
</div>
</dd>
</dl>

<!-- END OF ATTRIBUTE FILE modules/attributes/datatype.mhtml --><!-- INCLUDING ATTRIBUTE modules/attributes/property.mhtml -->
<dl class='attrDef'>
<dt><a class="adef" id="adef_metaAttributes_property"><span class="adef">property</span></a> = <span class="datatype"><a href="abstraction.html#dt_QName">QName</a></span></dt>

<dd>This attribute indicates which property is being defined by the element. If it is not specified, the property is <code>reference</code>.

<div class="example">
<p>Example</p>

<pre>
&lt;meta about="http://www.example.com/" property="dc:creator"&gt;John Smith&lt;/meta&gt;
</pre>
</div>

<p>Authors may use the following properties, listed here with their conventional interpretations.</p>

<p>User agents, search engines, etc. are free to interpret these properties as necessary.</p>

<p>The list of predefined values (in the XHTML2 namesapce) are given below. Users may extend this collection of relationships, however new values must be defined in their own namespace, and the
relationship names must be referenced in documents as qualified names (e.g., <code>dc:creator</code> for the Dublin Core "creator" relationship).</p>

<p>Note that in order to reference relationship definitions via QName, their namespace must be defined via an xmlns attribute somewhere suitable:</p>

<div class="example">
<p>Example</p>

<pre>
&lt;html ....  xmlns:dc="http://purl.org/dc/elements/1.1/"&gt;
</pre>
</div>

<dl>
<dt>description</dt>

<dd>Gives a description of the resource.</dd>

<dt>generator</dt>

<dd>Identifies the software used to generate the resource.</dd>

<dt>keywords</dt>

<dd>Gives a comma-separated list of keywords describing the resource.</dd>

<dt>reference</dt>

<dd>The default value, gives no explicit information about the relationship with the resource.</dd>

<dt>robots</dt>

<dd>Gives advisory information intended for automated web-crawling software. This specification does not define values for this property.</dd>

<dt>title</dt>

<dd>Specifies a title for the resource.</dd>
</dl>

<p>Note that previous versions of XHTML included an <code>author</code> property; this has now been replaced with the Dublin Core <code>creator</code> property.</p>

<p>Note that:</p>

<div class="example">
<p>Example</p>

<pre>
&lt;head&gt;
    &lt;title&gt;My Life and Times&lt;/title&gt;
</pre>
</div>

<p>is just a shorthand for:</p>

<div class="example">
<p>Example</p>

<pre>
&lt;head&gt;
    &lt;meta property="title"&gt;My Life and Times&lt;/meta&gt;
</pre>
</div>

<p>Note that the <a class="aref" href="mod-core.html#adef_core_title">title</a> attribute which is available on all XHTML2 elements, is just a shorthand for a common case:</p>

<div class="example">
<p>Example</p>

<pre>
&lt;a href="Jakob.html" title="Author biography"&gt;Jakob Nielsen&lt;/a&gt;'s Alertbox for January 11, 1998
</pre>
</div>

<p>is equivalent to:</p>

<div class="example">
<p>Example</p>

<pre>
&lt;meta about="#jakob" property="title"&gt;Author biography&lt;/meta&gt;
&lt;a href="Jakob.html" id="jakob"&gt;Jakob Nielsen&lt;/a&gt;'s Alertbox for January 11, 1998
</pre>
</div>

<p>Note that this allows you to specify richer, marked-up text for a title when needed.</p>
</dd>
</dl>

<!-- END OF ATTRIBUTE FILE modules/attributes/property.mhtml --><!-- INCLUDING ATTRIBUTE modules/attributes/rel.mhtml -->
<dl class='attrDef'>
<dt><a class="adef" id="adef_metaAttributes_rel"><span class="adef">rel</span></a> = <span class="datatype"><a href="abstraction.html#dt_QName">QName</a></span></dt>

<dd>This attribute describes the relationship between the resource specified by the <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_about">about</a> attribute (or its default value)
and the resource referred to by the <a class="aref" href="mod-hyperAttributes.html#adef_hyperAttributes_href">href</a> attribute.

<div class="example">
<p>Example</p>

<pre>
&lt;link href="top.html" rel="contents"/&gt;
</pre>
</div>

<p>This example defines a link to a table of contents for the current document.</p>

<div class="example">
<p>Example</p>

<pre>
&lt;link href="doc.ps"
      rel="alternate"
      media="print"
      hreftype="application/postscript" /&gt;
</pre>
</div>

<p>This example defines a link to an alternate version of the document especially suited to printing.</p>

<p>Authors may use the following relationship names, listed here with their conventional interpretations.</p>

<p>User agents, search engines, etc. may interpret these relationships in a variety of ways. For example, user agents may provide access to linked documents through a navigation bar.</p>

<p>Users may extend this collection of relationships. However, extensions must be defined in their own namespace, and the relationship names must be referenced in documents as qualified names (e.g.,
dc:creator for the Dublin Core "creator" relationship).</p>

<p>Note that in order to reference relationship definitions via QName, their namespace must be defined via an xmlns attribute somewhere suitable:</p>

<div class="example">
<p>Example</p>

<pre>
&lt;html ....  xmlns:dc="http://purl.org/dc/elements/1.1/"&gt;
</pre>
</div>

<dl>
<dt>alternate</dt>

<dd>Designates alternate versions for the document. When used together with the <a class="aref" href="mod-hyperAttributes.html#adef_hyperAttributes_hreflang">hreflang</a> attribute, it implies a
translated version of the document. When used together with the <a class="aref" href="mod-hyperAttributes.html#adef_hyperAttributes_hrefmedia">hrefmedia</a> attribute, it indicates a version intended
for that type of device.</dd>

<dt>start</dt>

<dd>Refers to the first resource in a collection of resources. A typical use case might be a collection of chapters in a book.</dd>

<dt>next</dt>

<dd>Refers to the next resource (after the current one) in an ordered collection.</dd>

<dt>prev</dt>

<dd>Refers to the previous resource (before the current one) in an ordered collection.</dd>

<dt>up</dt>

<dd>Refers to the resource "above" in a hierarchically structured set.</dd>

<dt>contents</dt>

<dd>Refers to a resource serving as a table of contents.</dd>

<dt>index</dt>

<dd>Refers to a resource providing an index.</dd>

<dt>glossary</dt>

<dd>Refers to a resource providing a glossary of terms.</dd>

<dt>copyright</dt>

<dd>Refers to a copyright statement for the resource.</dd>

<dt>chapter</dt>

<dd>Refers to a resource serving as a chapter in a collection.</dd>

<dt>section</dt>

<dd>Refers to a resource serving as a section in a collection.</dd>

<dt>subsection</dt>

<dd>Refers to a resource serving as a subsection in a collection.</dd>

<dt>appendix</dt>

<dd>Refers to a resource serving as an appendix in a collection.</dd>

<dt>help</dt>

<dd>Refers to a resource offering help (more information, links to other sources of information, etc.)</dd>

<dt>bookmark</dt>

<dd>Refers to a bookmark. A bookmark is a link to a key entry point within an extended document. The <a class="aref" href="mod-core.html#adef_core_title">title</a> attribute may be used, for example,
to label the bookmark. Note that several bookmarks may be defined for a document.</dd>

<dt>meta</dt>

<dd>Refers to a resource that provides metadata, for instance in RDF.</dd>

<dt>icon</dt>

<dd>Refers to a resource that represents an icon.</dd>

<dt>p3pv1</dt>

<dd>Refers to a P3P Policy Reference File. See [<a class="nref" href="references.html#ref_P3P">P3P</a>].</dd>

<dt>profile</dt>

<dd>
<p>Refers to a resource that defines relationships or provides metadata, for instance in RDF. User agents may use this URI in two ways:</p>

<ul>
<li>As a globally unique name. User agents may be able to recognize the name (without actually retrieving the profile) and perform some activity based on known conventions for that profile. For
instance, search engines could provide an interface for searching through catalogs of XHTML documents, where these documents all use the same profile for representing catalog entries.</li>

<li>As a link. User agents may dereference the URI and perform some activity based on the actual definitions within the profile (e.g., authorize the usage of the profile within the current XHTML
document). This specification does not define formats for profiles.</li>
</ul>

<p>This example refers to a hypothetical profile that defines useful properties for document indexing. The properties defined by this profile -- including "author", "copyright", "keywords", and
"date" -- have their values set by subsequent <a class="eref" href="mod-meta.html#edef_meta_meta">meta</a> declarations.</p>

<div class="example">
<p>Example</p>

<pre>
 &lt;html ... xmlns:mp="http://www.example.com/profiles/rels"&gt;
  &lt;head&gt;
      &lt;title&gt;How to complete Memorandum cover sheets&lt;/title&gt;
      &lt;link rel="profile" href="http://www.example.com/profiles/slideshow" /&gt;
  &lt;/head&gt;
  &lt;body&gt;
      &lt;div class="slide"&gt;
          some slide content...
      &lt;/div&gt;
  &lt;/body&gt;
...
</pre>
</div>
</dd>

<dt>role</dt>

<dd>Indicates the purpose of the resource. For some possible values, see <a href="mod-roleAttribute.html#s_roleAttributemodule">the Role Attribute</a> module.</dd>

<dt>cite</dt>

<dd>Refers to a resource that defines a citation (see <a class="eref" href="mod-text.html#edef_text_cite">cite</a>) .</dd>
</dl>

<div class="issue">
<p id="s_metaAttributesmodule_issue_0" class="issueTitle">Relationship 'required'</p>

Linktype 'required'</div>
</dd>
</dl>

<!-- END OF ATTRIBUTE FILE modules/attributes/rel.mhtml --><!-- INCLUDING ATTRIBUTE modules/attributes/rev.mhtml -->
<dl class='attrDef'>
<dt><a class="adef" id="adef_metaAttributes_rev"><span class="adef">rev</span></a> = <span class="datatype"><a href="abstraction.html#dt_QName">QName</a></span></dt>

<dd>This attribute is the complement of the <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_rel">rel</a> attribute and describes the reverse relationship between the resource
specified by the <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_about">about</a> attribute (or its default value) and the resource referred to by the <a class="aref" href=
"mod-hyperAttributes.html#adef_hyperAttributes_href">href</a> attribute. For a list of relationship names, see the <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_rel">rel</a>
attribute.

<div class="example">
<p>Example</p>

<pre>
&lt;link href="doc.html" rev="contents"/&gt;
</pre>
</div>

<p>This example states that the current document is the table of contents for the referenced document.</p>
</dd>
</dl>

<!-- END OF ATTRIBUTE FILE modules/attributes/rev.mhtml -->
<p>Implementation: <a href="relax_module_defs.html#a_rmodule_Metainformation_Attributes">RELAX NG</a></p>

<h2><a id="sec_24.2." name="sec_24.2.">24.2.</a> Meta and RDF</h2>

<p>The metadata attributes can be used to generate RDF statements, which consist of a subject, a predicate, and an object.</p>

<p>The attributes <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_rel">rel</a>, <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_rev">rev</a> and <a class="aref"
href="mod-metaAttributes.html#adef_metaAttributes_property">property</a> represent predicates. The predicate is obtained by concatenating the namespace URI and the local part of the QName of the
attribute value.</p>

<p>For attribute <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_rel">rel</a>, the subject is the <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_about">about</a>
property, and the object is the value of the <a class="aref" href="mod-hyperAttributes.html#adef_hyperAttributes_href">href</a> attribute; for attribute <a class="aref" href=
"mod-metaAttributes.html#adef_metaAttributes_rev">rev</a>, the subject and object roles are reversed: the subject is the <a class="aref" href="mod-hyperAttributes.html#adef_hyperAttributes_href">
href</a> attribute, and the object is the value of the <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_about">about</a> property.</p>

<p>For attribute <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_property">property</a>, the subject is the <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_about">
about</a> property, and the object is the string literal in the <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_content">content</a> attribute, or otherwise the XML literal that is
the content of the element, decorated as necessary with the value of the <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_datatype">datatype</a> attribute.</p>

<p>The about property is obtained as follows:</p>

<ul>
<li>If the element that the attributes are on has an <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_about">about</a> attribute, then that is used.</li>

<li>Otherwise for <a class="eref" href="mod-meta.html#edef_meta_meta">meta</a> and <a class="eref" href="mod-meta.html#edef_meta_link">link</a> elements:

<ul>
<li>If the parent element has an explicit <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_about">about</a> attribute, then that is the about property.</li>

<li>Otherwise, if the parent element has an <a class="aref" href="mod-core.html#adef_core_id">id</a> attribute, then that is the about property.</li>

<li>Otherwise, the about property is a 'blank node' representing the parent element (which is like an invisible automatically generated <a class="aref" href="mod-core.html#adef_core_id">id</a> on the
element).</li>
</ul>
</li>

<li>For all other elements, the about property is the closest <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_about">about</a> attribute on an ancestor of the current element. If
there is no such attribute, it is the [<a class="nref" href="references.html#ref_URI">URI</a>] of the containing document.</li>
</ul>

<h2><a id="sec_24.3." name="sec_24.3.">24.3.</a> Metadata as Content</h2>

<p>One use of the metadata attributes is with elements that represent document content, since the same string literal can be used to specify both document content, and metadata.</p>

<p>For example, articles often have the following repetitive structure, where the same values are used for metadata properties and actual content rendered to the reader:</p>

<div class="example">
<p>Example</p>

<pre>
  &lt;html xmlns="http://www.w3.org/2002/06/xhtml2/"
        xmlns:dc="http://purl.org/dc/elements/1.1/"&gt;
    &lt;head&gt;
      &lt;title&gt;... title ...&lt;/title&gt;
      &lt;meta property="dc:date"&gt;2004-03-23&lt;/meta&gt;
      &lt;meta property="dc:title"&gt;
            High-tech rollers hit casino for &amp;#163;1.3m
      &lt;/meta&gt;
      &lt;meta property="dc:creator"&gt;Steve Bird&lt;/meta&gt;
    &lt;/head&gt;
    &lt;body&gt;
      ...
      &lt;span class="date"&gt;2004-03-23&lt;/span&gt;
      &lt;span class="headline"&gt;
            High-tech rollers hit casino for &amp;#163;1.3m
      &lt;/span&gt;
      &lt;span class="byline"&gt;By Steve Bird&lt;/span&gt;
      &lt;span class="standfirst"&gt;
        Word of a hand-held device which can beat the roulette wheel
        has gambling bosses quaking
      &lt;/span&gt;
      ...
      &lt;p&gt;...&lt;/p&gt;
    &lt;/body&gt;
  &lt;/html&gt;
</pre>
</div>

<p>By making use of the meta attributes this can be shortened to the following:</p>

<div class="example">
<p>Example</p>

<pre>
  &lt;html xmlns="http://www.w3.org/2002/06/xhtml2/"
        xmlns:dc="http://purl.org/dc/elements/1.1/"&gt;
    &lt;head&gt;
      &lt;title&gt;... title ...&lt;/title&gt;
    &lt;/head&gt;
    &lt;body&gt;
      ...
      &lt;span property="dc:date"
          class="date"&gt;
          2004-03-23
      &lt;/span&gt;
      &lt;span property="dc:title"
          class="headline"&gt;
          High-tech rollers hit casino for &amp;#163;1.3m
      &lt;/span&gt;
      By &lt;span property="dc:creator"
               class="byline"&gt;Steve Bird&lt;/span&gt;
      &lt;span class="standfirst"&gt;
          Word of a hand-held device which can beat the
          roulette wheel has gambling bosses quaking
      &lt;/span&gt;
      ...
      &lt;p&gt;...&lt;/p&gt;
    &lt;/body&gt;
  &lt;/html&gt;
</pre>
</div>

<p>This is often easier to maintain since an author editing their document is at the same time editing the metadata.</p>

<h2><a id="sec_24.4." name="sec_24.4.">24.4.</a> Mapping Lexical Content</h2>

<p>Another use for the meta attributes on other mark-up elements is to provide a <em>normalized</em> value for some text. This is especially important to certain types of consumers of metadata, such
as search engines.</p>

<p>For example, the following article would be difficult to locate:</p>

<div class="example">
<p>Example</p>

<pre>
Tomorrow the &lt;span&gt;Prime Minister&lt;/span&gt; is expected to fly to ...
</pre>
</div>

<p>However, by using <a class="aref" href="mod-hyperAttributes.html#adef_hyperAttributes_href">href</a> and <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_content">content</a> we
can indicate exactly which Prime Minister is being referred to, and when the journey is due to take place:</p>

<div class="example">
<p>Example</p>

<pre>
&lt;span content="2004-03-20"&gt;Tomorrow&lt;/span&gt; the
&lt;span href="http://example.com/people/TonyBlair/1"&gt;Prime Minister&lt;/span&gt;
is expected to fly to ...
</pre>
</div>

<p>Note that if no <a class="aref" href="mod-metaAttributes.html#adef_metaAttributes_property">property</a> is present then the example just given is equivalent to:</p>

<div class="example">
<p>Example</p>

<pre>
&lt;span property="reference"
    content="2004-03-20"&gt;
    Tomorrow
&lt;/span&gt;
the &lt;span property="reference"
    href="http://example.com/people/TonyBlair/1"&gt;
    Prime Minister
&lt;/span&gt;
is expected to fly to ...
</pre>
</div>

<hr />
<div class="navbar">[<a href="mod-meta.html">previous</a>] &#160; [<a href="mod-object.html">next</a>] &#160; [<a href="Overview.html#toc">table of contents</a>] &#160;[<a href=
"elements.html">elements</a>] &#160;[<a href="attributes.html">attributes</a>]</div>
</body>
</html>