W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > May 2002

Re: user-defined datatype (facet) support needed?

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Wed, 31 Dec 1969 17:21:06 -0700
Message-Id: <p051015007c25b3a1bc7d@[130.107.66.138]>
To: Dan Connolly <connolly@w3.org>
Cc: w3c-rdfcore-wg@w3.org
>XML Schema has not only the 9 or so
>primitive types, but also bunch of facets
>for user-defined types ala "integers
>between 5 and 10".
>
>I don't think any of the recent datatyping
>proposals allows me to express that datatype.
>
>Is that a problem[ftf]?
>
>I suggest, tentatively, that it is.

I suggest it isn't.  Heres why: we shouldn't expect to be able to 
*express* a datatype in RDF. The actual definitions of the datatypes 
is done outside RDF, and RDF then *uses* the datatypes so defined 
(assuming they have somehow been given a special URI which can be 
used by an RDF engine to retrieve the relevant machinery). So if 
someone defines a datatype  like, say xsdd:integersBetweenFiveAndTen, 
then the RDF datatyping should work with that as well as with any 
other datatype. What that URI needs to 'supply' is well-defined:

1. A recognizer for members of the lexical space of the datatype.
2. A computable mapping from members of the lexical space to (some 
canonical representation of) members of the value space.

and that's all, in principle, though it wouldn't hurt to have a few 
others as well, eg an identity recognizer for lexical forms if (2) is 
expensive to compute.

>[crud; I was gonna write a bit more, but
>I've got another meeting. I think I better
>send this now, though, before I put it
>off for another three weeks...]
>
>[ftf] http://www.w3.org/2001/sw/RDFCore/20020225-f2f/#d-2002-02-26-3
>
>
>--
>Dan Connolly, W3C http://www.w3.org/People/Connolly/


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Received on Thursday, 2 May 2002 15:19:41 EDT

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