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Re: ACTION 2002-01-24#4 responses on datatyping

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Wed, 6 Feb 2002 13:06:08 -0600
Message-Id: <p0510143db8872a87f543@[65.212.118.208]>
To: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org
>On RDF comments at least two topics have come up:
>
>The URI for XML Schema datatypes:
>
>http://lists.w3.org/Archives/Public/www-rdf-comments/2002JanMar/0029.html
>[[[
>Please do not bind the "xsd" prefix to the http://www.w3.org/2001/XMLSchema #
>namespace name. Furthermore, please do not refer to this namespace name as
>the XML Schema namespace, in fact the two _namespaces_ are entirely
>unrelated.
>]]]
>
>
>and
>
>query and datatypes:
>
>http://lists.w3.org/Archives/Public/www-rdf-comments/2002JanMar/0053.html
>
>e.g.
>
>
>[[[
>In that case I'd be against this [TDL global idiom], because normally I
>don't rely on
>having the schema (or schema-like constraints) available when you make
>a query, and because I prefer to make explicit queries.
>]]]
>
>
>I propose that both of these be treated as issues requiring substantive
>response:
>   - URIs for datatyping

re. that, my proposal is to have an explicit RDF assertion that an 
uriref ddd is being treated as a datatype in a graph, by using

ddd rdf:type rdf:Datatype .

(never mind about the rdfd idea.)
This usage should cause a datatype-aware RDF engine to retrieve or 
access some useable specification of the dataype in question. This 
should be sufficient, at a minimum, to enable it to then
(a) recognize whether a literal conforms to the lexical form required 
by that datatype
(b) generate a canonical internal representation of the value of such 
a literal under the lexical-to-value mapping of that datatype, 
suitable for use by external applications, and
(c) test such representations of values for equality.
(It might be helpful to have other abilities, such as generating a 
canonical lexical form from a value representation,  transforming 
lexical forms to canonical forms, or testing lexical forms for 
identity.)
This would enable the RDF engine to check the graph for datatype 
consistency, and to maintain APIs between the graph and external 
applications.

In other words, the uriref for the datatype has to provide access to 
quite a bit more than simply a namespace.

>   - how a non-schema aware application processes global type idioms.

I think that is pretty clear in the latest proposal. Literals are 
simply text strings, and can be tested for exact identity, but very 
little else, without any awareness of any datatyping schema. Range 
assertions have their usual meaning, but no particular inference can 
be made from a range assertion to an rdf:dtype  assertion; but then 
rdf:dtype carries essentially the same content as rdf:type, and has 
no 'extra' meaning, in this case; and rdf:value is almost vacuous 
(and any subproperties of it).

None of this is wrong, exactly, but it doesn't really 'do' anything 
much until you add datatypes to it, and then it kind of springs into 
life.

Pat
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Received on Wednesday, 6 February 2002 14:05:35 EST

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