XHTML+RDFa (Extensible Hypertext Markup Language + Resource Description Framework in attributes)
is an extended version of the
XHTML
markup language
for supporting
RDF
through a collection of attributes and processing rules in the form of
well-formed
XML
documents. XHTML+RDFa is one of the techniques used to develop
Semantic Web
content by embedding rich semantic markup.
Version 1.1 of the language is a superset of
XHTML 1.1
, integrating the attributes according to
RDFa
Core 1.1. In other words, it is an
RDFa
support through
XHTML Modularization
.
RDFa
in
XHTML
version 1.0 became a
World Wide Web Consortium
(W3C)
Recommendation
on 14 October 2008.
[1]
[2]
The current recommendation is
RDFa
+
XHTML
version 1.1, which became a W3C Recommendation on 7 June 2012
[3]
and was updated with a ”Second Edition” on 22 August 2013
[4]
and a ”Third Edition” on 17 March 2015.
[5]
Version 1.1 is based on
XHTML™ 1.1 - Module-based XHTML - Second Edition
. Version 1.0 was based on the first edition.
Overview
[
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]
Conventional Web documents contain large amounts of structured data that can be rendered in
web browsers
. This approach works fine for publishing purposes, however, a large amount of data stored in
Web documents
cannot be processed this way. XHTML+RDFa can provide
machine-readable
metadata
within the
markup code
which makes additional user functionalities available. Most important of all, actions can be performed automatically that enables up-to-date publishing, structured search and sharing.
[6]
RDFa can serve as a bridge between the "human and data webs".
[7]
The potential in web documents enriched with RDFa is increasing since major search engines begin to process them while indexing. Yahoo indexes
RDFa
and microformats since 2008 and Google since 2009.
[8]
The
RDFa
attribute specifications make it possible to describe structured data in any
markup language
. The
RDFa
markup in XHTML+RDFa reuses the
markup code
, thus eliminating the need for unnecessary duplications.
XHTML+RDFa is not widely distributed yet, probably due to the lack of support in authoring tools and
content management systems
.
[9]
However, there is good tendency.
Drupal
7, for example, supports
RDFa
.
[10]
Since the “a” in RDFa stands for attributes, it is straightforward to use
CSS selectors
to style the code.
[11]
Document Type Definition
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The combination of
XHTML 1.1
and
RDFa
modules is claimed to be an example
markup language
. The Document Type Definition (DTD) is published at the
W3C
website.
[12]
According to the
document type declaration
, the identifiers of an XHTML+RDFa document should look like the following:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.1//EN"
"http://www.w3.org/MarkUp/DTD/xhtml-rdfa-2.dtd">
An example XHTML+RDFa document:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.1//EN"
"http://www.w3.org/MarkUp/DTD/xhtml-rdfa-2.dtd">
<html
version=
"XHTML+RDFa 1.1"
xmlns=
"http://www.w3.org/1999/xhtml"
xml:lang=
"en"
lang=
"en"
>
<head>
<title>
XHTML+RDFa
document
example
</title>
</head>
<body>
...
</body>
</html>
Authoring
[
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The
RDFa
metadata
is embedded as an
XHTML
attribute of the document element, generally the
XHTML
tag. The annotation syntax provided by RDFa can be used to express
RDF
statements in
XHTML
documents.
[13]
Validation
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XHTML+RDFa documents can be validated individually online at the
W3C Markup Validation Service
or together with
CSS
and
RSS
at
W3C Unicorn
. The validity of XHTML+RDFa documents can be indicated by the XHTML+RDFa
conformance icons
of
W3C
.
Examples
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XHTML syntax, additional namespaces and semantic markup.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.1//EN"
"http://www.w3.org/MarkUp/DTD/xhtml-rdfa-2.dtd">
<html
version=
"XHTML+RDFa 1.1"
xmlns=
"http://www.w3.org/1999/xhtml"
xmlns:contact=
"http://www.w3.org/2000/10/swap/pim/contact#"
xmlns:foaf=
"http://xmlns.com/foaf/0.1/"
xmlns:rdfs=
"http://www.w3.org/2000/01/rdf-schema#"
xmlns:xsd=
"http://www.w3.org/2001/XMLSchema#"
xml:lang=
"en"
lang=
"en"
>
<head>
<title>
XHTML+RDFa
example
</title>
<meta
http-equiv=
"Content-Type"
content=
"application/xhtml+xml; charset=utf-8"
/>
<meta
http-equiv=
"Content-Style-Type"
content=
"text/css"
/>
<meta
name=
"content-language"
content=
"en"
/>
<meta
name=
"robots"
content=
"index, follow"
/>
<link
rel=
"schema.DC"
href=
"http://purl.org/dc/elements/1.1/"
/>
<link
rel=
"schema.DCTERMS"
href=
"http://purl.org/dc/terms/"
/>
<link
rel=
"alternate"
type=
"application/rss+xml"
title=
"Feed channel of XHTML+RDFa example page"
href=
"http://www.example.com/rss.xml"
/>
<meta
name=
"DC.title"
content=
"XHTML+RDFa example"
/>
<meta
name=
"DC.subject"
content=
"XHTML+RDFa, semantic web"
/>
<meta
name=
"DC.description"
content=
"Example for Extensible Hypertext Markup Language + Resource Description Framework ? in ? attributes."
/>
<meta
name=
"DC.format"
content=
"application/xhtml+xml"
/>
<meta
name=
"DC.language"
content=
"en"
/>
<link
rel=
"shortcut icon"
href=
"favicon.ico"
/>
<link
rel=
"stylesheet"
type=
"text/css"
href=
"main.css"
title=
"main styles"
/>
<link
rel=
"foaf:primaryTopic"
type=
"application/rdf+xml"
title=
"FOAF"
href=
"http://www.example.com/metadata/foaf.rdf"
/>
<script
type=
"text/javascript"
src=
"js/click.js"
></script>
</head>
<body>
<div
class=
"content"
>
<p>
<span
property=
"foaf:name"
>
Jerry
Smith
</span><br
/>
<i>
Senior
developer,
QA
</i><br
/>
<a
title=
"More about me"
rel=
"rdfs:seeAlso"
href=
"about.htm"
>
More...
</a>
</p>
<p
rel=
"contact:address"
>
93
Rose
Ave
<br
/>
<a
property=
"contact:city"
rel=
"rdfs:seeAlso"
title=
"Adelaide on Wikipedia"
resource=
"http://dbpedia.org/resource/Adelaide"
href=
"http://en.wikipedia.org/wiki/Adelaide"
>
Adelaide
</a>
</p>
<p>
<span
rel=
"foaf:phone"
resource=
"tel:+6112345678"
>
+61
12/345-678
</span>
</p>
</div>
</body>
</html>
See also
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References
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Products and
standards
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Organizations
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Community & business groups
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Closed groups
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Software
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Conferences
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Background
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Sub-topics
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Applications
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Related topics
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Standards
| Syntax and supporting technologies
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Schemas, ontologies and rules
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Semantic annotation
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Common vocabularies
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Microformat vocabularies
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