From: Dan Connolly (connolly@w3.org)
Date: 10/04/01
"Peter F. Patel-Schneider" wrote:
[...]
> 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.
Yes and no... it's somewhat appealing, but it conflicts
with a certain amount of deployed code. That's not
necessarily a complete show-stopper, but it's something
that the RDF Core WG is bound to give consideration to.
Hmmm... after mulling it over (details below) I think
I could support this proposal, at from the joint-committee
perspective.
> 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" .
It's a way. As I've said, you can get the same information
without breaking assumptions in deployed code ala:
Mary age "07".
age ??:valueProperty ageInt.
ageInt rdfs:range dt:integer.
> 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.
The status quo for interpreting literals is not "an uninterpreted
quasi-character space." The status quo is just plain unclear.
So just say:
1/ Decide that the value space for literals is 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.
any? which one? I think a precise formulation is a little
more involved than this, but from the stuff below, I get
the idea...
> 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
I looked there several times during the development of DAML+OIL
and never found the explanation
of what's going on here. Could you tell me which text explains
it?
> 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.
i.e.
(exists (?x) (and (age John ?x) (lexicalRep ?x "5"))
which, I suggest, is more naturally represented as:
John age _:x.
_:x lexicalRep "5".
i.e. some folks will see this as putting another
RDF node and arc in the graph. That doesn't bother
me, but it bothers some folks a lot.
but back to your proposal...
> 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.
I'm afraid there's a lot of deployed RDF code that concludes
they're the same. I'm not certain how much, though. It would
be worth collecting some info.
Now literals are in such a state that this sort of mass fix
might be deployable, but I'm not at all sure...
> 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" />
don't forget that rdf:resource takes a full URI,
not a qname.
> </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>
--
Dan Connolly, W3C http://www.w3.org/People/Connolly/
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