RDFa (Resource Description Framework in Attributes) is a W3C Recommendation that adds attribute-level extensions to HTML, XHTML, and XML-based document types for embedding rich metadata within web documents. The Resource Description Framework data-model mapping enables the use of RDFs for embedding RDF subject-predicate-object expressions within XHTML documents. RDFa also enables the extraction of RDF model triples by compliant user agents.
๐ History
RDFa was first proposed by Mark Birbeck in the form of a W3C note entitled XHTML and RDF, presented to the Semantic Web Interest Group at the W3C’s 2004 Technical Plenary. Later that year the work became part of the sixth public Working Draft of XHTML 2.0. The purpose of RDFa was always to provide a way to add metadata to any XML-based language.
๐ Key Milestones
In April 2007 the XHTML 2 Working Group produced a module to support RDF annotation within the XHTML 1 family. October 2007 saw the first public Working Draft of a document entitled RDFa in XHTML: Syntax and Processing. In October 2008 RDFa 1.0 reached recommendation status. RDFa 1.1 reached recommendation status in June 2012.
๐ง Variants and Standards
RDFa Lite is a W3C Recommendation (1.0 and 1.1) since 2009, consisting of five attributes: vocab, typeof, property, resource, and prefix. RDFa 1.1 Lite is upwards compatible with RDFa 1.1. The “HTML+RDFa” syntax of 2008 was also termed “RDFa 1.0”, so there is no “RDFa Core 1.0” standard.
๐ Usage Statistics
As of 2013 these standards were encoding events, contact information, products, and so on. The statistics of 2017 show that usage of HTML+RDFa is now less than that of Microformats.
| Version | Year | Status | Key Feature |
|---|---|---|---|
| RDFa 1.0 | 2008 | Recommendation | First RDFa standard for XHTML |
| RDFa 1.1 | 2012 | Recommendation | No longer relies on XML-specific namespace mechanism |
| RDFa Lite 1.0/1.1 | 2009 | Recommendation | Five attributes: vocab, typeof, property, resource, prefix |
| HTML+RDFa 1.1 | 2015 | Standard | Support for RDFa in HTML4 and HTML5 |