From: Peter F. Patel-Schneider (pfps@research.bell-labs.com)
Date: 10/04/01
Hi: Here is a little document that I prepared. It takes (most) of the datatype ideas from DAML+OIL (March 2001) and recasts them informally as an extension to RDF Schema. Now for the political part: 1/ I think it would be better if this were to come from the joint committee. Can we discuss this at the next meeting and adopt it (or not)? 2/ Things are moving fast on the RDF front, so if the joint committee can't make a decision soon, I may have to unilaterally reluctantly decide to push it out from just me. 3/ Where should this go? I'm almost of the opinion that it should go to the Semantic Web coordination group instead of the RDF Core Working Group. Comments, please. peter Adding Datatypes to RDF Schema Peter F. Patel-Schneider Here is a method for adding datatypes to RDF Schema that fits well with what I see as the RDF Schema philosophy. INTRODUCTION First some desiderata: 1/ The datatype scheme should be backward compatible with RDF and RDF Schema as they are currently constituted. From this, I get that the following n-triples should still be allowed: John age "5" . John streetAddress "12a" . Mary streetAddress "5" . 2/ The datatype scheme should allow type information to be specified in the same way that RDF Schema provides ``type'' information for resources. From this, I get that the following is a (or, perhaps, the) way to specify the type of a literal: Mary age "07" . age rdfs:range ????:integer . John age "05" . THE PROPOSAL The basic idea of the proposal is quite simple. 1/ Change the value space for literals from an uninterpreted quasi-character space to the disjoint union of a collection of value spaces. 2/ Allow untyped literals to denote any element of this value space for which they are lexical representations. 3/ Use special URIs to refer to these value spaces and incorporate their meaning into the meaning of RDF Schema. For technical details on one way to do something very close to this, see the model theory for DAML+OIL at http://www.daml.org/2001/03/model-theoretic-semantics.html What sort of URIs and value spaces could be used? Just about any kind. Primitive XML Schema datatypes would work and will be used in the following examples. The mechanism can be extended to all XML Schema datatypes and with some extensions probably even to all of XML Schema. EXAMPLES AND COMMENTARY A n-triple example using XML Schema datatypes: John age "5" . All that is known so far is that John's age is some data value that can be lexicalized as 5. John streetAddress "05" . Mary streetAddress "5" . It is not know yet whether John's age is the same data value as Mary's street address. Also John and Mary could turn out to have the same streetAddress John age "05" . It is not known yet whether John has two ages. age rdfs:range xsd:integer . Now we know that the two statements about John's age denote the same information. streetAddress rdfs:range xsd:string . Now we know that John's street address is different from Mary's street address. An RDF/XML version of more-or-less the above example: <rdf:RDF> .... <rdf:Property rdf:ID="streetAddress"> <rdfs:range rdf:resource="xsd:string" /> </rdf:Property> <Person rdf:ID="John"> <age>5</age> <streetAddress>05</streetAddress> </Person> <Person rdf:ID="Mary"> <streetAddress>5</streetAddress> </Person> <Person rdf:about="John"> <age>05</age> </Person> .... <rdf:Property rdf:ID="age"> <rdfs:range rdf:resource="xsd:integer" /> </rdf:Property> </rdf:RDF>
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