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RDF has a standard XML syntax which has nice merging properties but isn't so nice for authors and doesn't integrate well with DTDs, XML Schemas, and the like. There will always be various alternative formats that can be used to encode information and publish it as structured data on the Web. In order to make this information available to RDF systems, some sort of pre-processing is necessary. This page collects general approaches and concrete mappings.


GRDDL is a technique for processing XML/XHTML dialects (especially microformats) as custom RDF syntaxes by having each document point, directly or indirectly, to a transformation to an RDF graph. GRDDL accomodates a wide variety of dialects (at the expense of asking consumers to execute potentially untrusted code). In theory, GRDDL can be combined with arbitrary transformation mechanisms, for now it's mostly based on XSLTs.

RDFa and eRDF are designs for serializing RDF in HTML. They allow a single parser (or GRDDL transformation!) to work for data from any domain and provide a direct relationship between the RDF data and the HTML document structure, which can improve human interaction with enriched Web content (e.g. for copy-and-paste of information).

Custom parsers can be used to convert a particular serialization to RDF. Dialect-specific parsers can be valuable for non-XML/tagsoup formats, or in systems where XSLT is not an efficient approach.

HTML-based Dialects

Dialect Domain Schema Mapping Status
Dublin Core in HTML (legacy) Bibliographic Metadata Dublin Core dc-extract Valid 2003-2003, now superseded
Dublin Core in HTML (current) Bibliographic Metadata Dublin Core dc-html2rdfxml.xsl Maintained by DCMI
eRDF generic RDF extract-rdf.xsl, profile by IanDavis
GeoURL markup Geo (lat/long) GeoInfo grokGeoURL.xsl e.g. Joe Lambda's homepage
glink HTML links/link@rel #html, DC groklinks.xsl maintained by DannyAyers
hCalendar Calendars and Events RDF Calendar glean-hcal.xsl, hcal profile maintained by DanConnolly since Dec 2002
hCard Contact Information vcard ontologies (2006) hcard2rdf.xsl, hcard profile maintained by Walsh, Halpin, and Suda since Nov 2006; used in xtech schedule
hDoap Software project description DOAP hDoap maintained by DannyAyers
hReview Opinions, Ratings and Reviews RDF Review hreview2rdfxml.xsl See RDF Review
hTurtle generic RDF XSLT service, profile by SeanPalmer
metaprof meta/link@rel + generic various xh2rdf.xsl maintained by MasahideKanzaki
RDFa generic RDF RDFa profile by Fabien Gandon, collaborating with the GRDDL and RDFa WGs
Rel-License Licenses Creative Commons grokCC.xsl e.g. Joe Lambda's homepage
Rel-Tag Tags, Keywords, Categories Tag Ontology, SKOS, DC  ? (todo DannyAyers)
Site Summaries Syndication RSS html2rss.xsl in production on the W3C homepage
XFN Social Graph XFN + # as namespace grokXFN.xsl maintained(?) by DanConnolly
Site Summaries Syndication RSS html2rss.xsl in production on the W3C homepage
XFN Social Graph XFN+hCard as FoaF hFoaF.xsl Maintained by MartinMcEvoy
hAudio Audio Syndication hAudio as Music Ontology Mo-hAudio.xsl Maintained by MartinMcEvoy
RDF-3T generic RDF RDF-3T Maintained by MartinMcEvoy

Non-HTML based dialects

Dialect Domain Schema Mapping
RSS Syndication RSS 1.0 feed-rss1.0.xsl
Atom Syndication Atom/OWL atom2rdf_xslt-1.0.xsl
Atom Syndication RSS 1.0 atom2rss10.xsl
OPML Feedlists FOAF/RSS 1.0 opml2blogroll.xsl
OPML Feedlists FOAF/RSS 1.0/SKOS opml2skosroll.xsl
Metalink File sharing metalink (under revision 2007-10)
APML Attention Profiling apml -
SAWSDL web service description SAWSDL profile, SAWSDL_GRDDL.xsl
XTM topic maps XTM profile, XTM_GRDDL.xsl
  • there are several other XSLTs around, discussion is in-progress on which is best for Atom/GRDDL
  • * OPML tends to be used ad hoc, it's only minimally specified and data in the wild varies wildly, hence it's impossible to give definitive mappings

migrating from MicroModels, grddlmicromodels, EmbeddingRDFinHTML, CustomRdfDialects/GrddableMicroformats, etc.