XHTML+RDFa (Extensible Hypertext Markup Language + Resource Description Framework in attributes) is an extended version of the
XHTML
Extensible HyperText Markup Language (XHTML) is part of the family of XML markup languages which mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which Web pages are formulated.
While HTML, pr ...
markup language
A markup language is a Encoding, text-encoding system which specifies the structure and formatting of a document and potentially the relationships among its parts. Markup can control the display of a document or enrich its content to facilitate au ...
for supporting RDF through a collection of attributes and processing rules in the form of well-formed
XML
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding electronic document, documents in a format that is both human-readable and Machine-r ...
documents. XHTML+RDFa is one of the techniques used to develop
Semantic Web
The Semantic Web, sometimes known as Web 3.0, is an extension of the World Wide Web through standards set by the World Wide Web Consortium (W3C). The goal of the Semantic Web is to make Internet data machine-readable.
To enable the encoding o ...
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
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
Core 1.1. In other words, it is an
RDFa
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
support through
XHTML Modularization XHTML modularization is a methodology for producing modularized markup languages in a number of different schema languages (currently DTDs, XML Schema and Relax NG) so that the modules can easily be plugged together to create markup languages.
Alt ...
.
RDFa
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
in
XHTML
Extensible HyperText Markup Language (XHTML) is part of the family of XML markup languages which mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which Web pages are formulated.
While HTML, pr ...
version 1.0 became a
World Wide Web Consortium
The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working together in ...
(W3C) Recommendation on 14 October 2008.
The current recommendation is
RDFa
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
+
XHTML
Extensible HyperText Markup Language (XHTML) is part of the family of XML markup languages which mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which Web pages are formulated.
While HTML, pr ...
version 1.1, which became a W3C Recommendation on 7 June 2012 and was updated with a ”Second Edition” on 22 August 2013 and a ”Third Edition” on 17 March 2015.
Version 1.1 is based o XHTML™ 1.1 - Module-based XHTML - Second Edition Version 1.0 was based on the first edition.
Overview
Conventional Web documents contain large amounts of structured data that can be rendered in
web browsers
A web browser, often shortened to browser, is an application for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's scree ...
. 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
In communications and computing, a machine-readable medium (or computer-readable medium) is a medium capable of storing data in a format easily readable by a digital computer or a sensor.
It contrasts with ''human-readable'' medium and data.
T ...
metadata
Metadata (or metainformation) is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including:
* Descriptive ...
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.
RDFa can serve as a bridge between the "human and data webs".
The potential in web documents enriched with RDFa is increasing since major search engines begin to process them while indexing. Yahoo indexes
RDFa
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
and microformats since 2008 and Google since 2009.
The
RDFa
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
attribute specifications make it possible to describe structured data in any
markup language
A markup language is a Encoding, text-encoding system which specifies the structure and formatting of a document and potentially the relationships among its parts. Markup can control the display of a document or enrich its content to facilitate au ...
. The
RDFa
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
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
A content management system (CMS) is computer software used to manage the creation and modification of digital content (content management).''Managing Enterprise Content: A Unified Content Strategy''. Ann Rockley, Pamela Kostur, Steve Manning. New ...
. However, there is good tendency.
Drupal
Drupal () is a free and open-source web content management system (CMS) written in PHP and distributed under the GNU General Public License. Drupal provides an open-source back-end framework for at least 14% of the top 10,000 websites worldwide ...
7, for example, supports
RDFa
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
.
Since the “a” in RDFa stands for attributes, it is straightforward to use CSS selectors to style the code.
RDFa
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
modules is claimed to be an example
markup language
A markup language is a Encoding, text-encoding system which specifies the structure and formatting of a document and potentially the relationships among its parts. Markup can control the display of a document or enrich its content to facilitate au ...
. The Document Type Definition (DTD) is published at the
W3C
The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working together in ...
website.
According to the
document type declaration
A document type declaration, or DOCTYPE, is an instruction that associates a particular XML or SGML document (for example, a web page) with a document type definition (DTD) (for example, the formal definition of a particular version of HTML 2.0 - ...
, the identifiers of an XHTML+RDFa document should look like the following:
An example XHTML+RDFa document:
XHTML+RDFa document example
...
Authoring
The
RDFa
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within web documents. The Resource Descript ...
metadata
Metadata (or metainformation) is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including:
* Descriptive ...
is embedded as an
XHTML
Extensible HyperText Markup Language (XHTML) is part of the family of XML markup languages which mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which Web pages are formulated.
While HTML, pr ...
attribute of the document element, generally the
XHTML
Extensible HyperText Markup Language (XHTML) is part of the family of XML markup languages which mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which Web pages are formulated.
While HTML, pr ...
tag. The annotation syntax provided by RDFa can be used to express RDF statements in
XHTML
Extensible HyperText Markup Language (XHTML) is part of the family of XML markup languages which mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which Web pages are formulated.
While HTML, pr ...
documents.
Validation
XHTML+RDFa documents can be validated individually online at the
W3C Markup Validation Service
The Markup Validation Service is a validator by the World Wide Web Consortium (W3C) that allows Internet users to check pre-HTML5 HTML and XHTML documents for Well-formed element, well-formed markup against a document type definition (DTD). Marku ...
RSS
RSS ( RDF Site Summary or Really Simple Syndication) is a web feed that allows users and applications to access updates to websites in a standardized, computer-readable format. Subscribing to RSS feeds can allow a user to keep track of many ...
W3C
The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working together in ...
.
Examples
XHTML syntax, additional namespaces and semantic markup.
XHTML+RDFa example
HTML
Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is often assisted by technologies such as Cascading Style Sheets ( ...
*
List of XML and HTML character entity references
In SGML, HTML and XML documents, the logical constructs known as ''character data'' and ''attribute values'' consist of sequences of characters, in which each character can manifest directly (representing itself), or can be represented by a series ...
*
Microdata (HTML)
Microdata is a WHATWG HTML specification used to nest metadata within existing content on web pages. Search engines, web crawlers, and browsers can extract and process Microdata from a web page and use it to provide a richer browsing experience ...