RDF literals

From: pat hayes (phayes@ai.uwf.edu)
Date: 11/05/02

  • Next message: Boley, Harold: "RE: Slides "RuleML Meets RDF" for today's Joint Committee telecon and RDF's bNodes"
    Guys, I wonder if you might find RDF typed literals useful? These 
    consist of a literal string plus a uriref which is supposed to 
    indicate a datatype, and the convention is that in 'datatyped RDFS' 
    they denote the value of the string under the lexical2value mapping 
    of that datatype, eg "100"^^xsd:number  (Ntriples notation) denotes a 
    hundred. (If there is no such datatype, they essentially act like an 
    unknown uriref: ie they denote something but the reasoner don't know 
    what.)  The point that we havn't emphasized is that RDF is not itself 
    restricted to any particular collection of datatypes, so you are free 
    to invent your own and to use them in RDF, and the result is legal 
    RDF. For these purposes, what counts as a datatype is something which
    1. defines a class of legal lexical forms (strings)
    2. defines a mapping from the class of lexical forms to some class of values
    2a. in practice, is able to provide an algorithm for computing the 
    pullback of identity under the inverse of the mapping on the lexical 
    space (eg by computing a canonical lexical form though tha s not the 
    only way)
    3. has a uriref.
    So, for example, one way you could use literals to encode, say, 
    urirefs and obey the RDF thought police would be to use xsd:anyURI as 
    a datatype; similarly for XML and rdfS:XMLLiteral; and similarly for 
    any other thing you wanted to encode (invent your own dataype and 
    <yourdatatypeURI>. rdf:type rdfs:Datatype .
    to keep the RDFS parsers happy.)
    Of course you can define your own rdfs:subClassOf rdfs:Datatype and 
    have rules which apply to it. In fact, if you want to get creative, 
    it could also *be* an rdfs:Datatype.... :-)
    Best wishes
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