'''RDF''' or '''Resource Description Framework''' is a generic model for describing objects and data. The basic unit of RDF is the triple, which consists of a subject, predicate, and object.

== Representations ==

RDF/XML is a common representation, and unfortunately is intimidating, miserable to work with by hand, and just barely gets by as human unreadable (it's designed for machine consumption).

RDF/N-triples (aka RDF/N3) is a quick-and-easy representation by Tim-Berners Lee. He has a [[http://www.w3.org/2000/10/swap/Primer|beginner's N3 primer]].

[[http://www.w3.org/TeamSubmission/turtle/|Turtle]] is another natural language-looking, N3-like syntax by Dave Beckett.

[[http://n2.talis.com/wiki/RDF_JSON_Specification|RDF/JSON]] is a description for RDF in JSON, perfect for use in browser-based web applications. Freebase also uses some kind of RDF-in-JSON representation, though different.

[[http://json-ld.org/|JSON-LD]] (JSON for Linked Data) is another RDF-in-JSON format which appears to be easier to integrate into existing JSON documents (à la adds namespacing to JSON).

Dave Beckett has a [[http://journal.dajobe.org/journal/posts/2010/01/24/rdf-syntaxes-2-0/|summary on various RDF representations in 2010]].

== RDFa ==

'''RDFa''' is a mechanism for embedding RDF triples in HTML attributes.

=== Discussion ===

 * [[http://www.jenitennison.com/blog/node/124|HTML5/RDFa arguments]]: why RDFa isn't being included in HTML5

=== Representing dates ===

Since HTML5's <time> element is dead, something like:

{{{#!highlight html
<span property="dc:date">2011-11-03</span>
}}}

or 

{{{#!highlight html
<span prefix="dc: http://purl.org/dc/elements/1.1/ xsd: http://www.w3.org/2001/XMLSchema" property="dc:date" content="2011-11-03T03:00Z" datatype="xsd:datetime">
Nov 03, 2011
</span>
}}}

where the date is represented in [[http://www.w3.org/TR/NOTE-datetime|W3CDTF]] (a variant of ISO 8601).


=== Competing formats ===

Microformats are oriented around special attribute values that go into elements' class= attributes. It has no support for namesspaces. It is not compatible with RDF.

Microdata is a section of the draft [[HTML5]] specification that adds a set of new attributes (itemprop, etc) to better expose data than microformats. Has some kind of support for namespaces. It can be made compatible with RDF.

 * [[http://blog.foolip.org/2009/08/23/microformats-vs-rdfa-vs-microdata/|Microformats vs RDFa vs Microdata]]: great article contrasting the three competing formats

== Ontologies ==

 * [[http://www.w3.org/2011/rdfa-context/rdfa-1.1|Widely-used vocabularies in RDFa v1.1]]
 * [[http://www.w3.org/wiki/TaskForces/CommunityProjects/LinkingOpenData/CommonVocabularies|List of Common vocabularies]], from a W3C wiki page
 * [[http://bioportal.bioontology.org/ontologies|Biology-related ontologies]]