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February 15, 2010

VCard in RDF

Via a post to the W3C Semantic Web Interest Group mailing list from Renato Iannella, I noticed that the W3C has published an updated specification for expressing vCard data in RDF, Representing vCard Objects in RDF.

A comment from the W3C Team provides some of the background to the document, and explains that it represents a consolidation of an earlier (2001) formulation of vCard in RDF by Renato published by the W3C and a subsequent ontology created by Norman Walsh, Brian Suda and Harry Halpin, the latter also used, at least in part, by Yahoo SearchMonkey (see Local, Event, Product, Discussion).

The new document also provides an answer to a question which I've been unsure about for years: whether the class of vCards was disjoint with the class of "agents" (e.g. persons or organisations). Or, to put it another way, I wasn't sure whether the properties of a vCard could be used to describe persons or organisations, e.g. "this document was created by the agent with the vCard name 'John Smith'":

@prefix dc: <http://purl.org/dc/terms/> .
@prefix v: <http://www.w3.org/2006/vcard/ns#> .
 <> dc:creator
  [
    v:fn "John Smith"
  ] .

(This, I think, is the pattern recommended by Yahoo SearchMonkey: see, for example, the extended "product" example where the manufacturer of a product is an instance of both the v:VCard class and the commerce:Business class.)

The alternative would be that those properties had to be used to describe a vCard-as-"document" (or as something other than agent, at least), which was in turn related to a person or organisation, e.g. "this document has created by the agent who "has a vCard" with the vCard name 'John Smith'" (I invented an example "hasVCard" property here):

@prefix dc: <http://purl.org/dc/terms/> .
@prefix v: <http://www.w3.org/2006/vcard/ns#> .
@prefix ex: <http://example.org/terms/> .
 <> dc:creator
  [
    ex:hasVCard
     [
       v:fn "John Smith"
     ]
 ] .

To keep the examples brief I used blank nodes in the above examples, but URIs might have been used to refer to the vCard and agent resources too.

In its description of the VCard class, the new document says: Resources that are vCards and the URIs that denote these vCards can also be the same URIs that denote people/orgs. That phrasing seems a bit awkward, but the intent seems pretty clear: the classes are not disjoint, a single resource can be both a vCard and a person, and the properties of a vCard can be applied to a person. So I can use the pattern in my first example above without creating any sort of contradiction, and the second pattern is also permitted.

One consequence of this is that consumers of data need to allow for both patterns - in the general case, at least, though it may be that they have additional information that within a particular dataset only a single pattern is in use.

In the example above, I used an example.org URI for the property that relates an agent to a vCard. The discussion on the list highlights that there are a couple of contenders for properties to meet this requirement: (ov:businessCard from Michael Hausenblas and hcterms:hasCard from Toby Inkster. A proposal to add such a property to the FOAF vocabulary has been made on the FOAF community wiki.

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