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RE: questions about rdfs:Datatype [Was: RE: Seeking normative definition of datatyping]

From: <Art.Barstow@nokia.com>
Date: Tue, 3 Dec 2002 09:20:12 -0500
Message-ID: <5C76D29CD0FA3143896D08BB1743296AB0033D@bsebe001.americas.nokia.com>
To: <bwm@hplb.hpl.hp.com>
Cc: <www-rdf-comments@w3.org>

Hi Brian,

> From: ext Brian McBride [mailto:bwm@hplb.hpl.hp.com]
> Do let us know if you find this too confusing.

Since the Primer is 100% Informative, it has equivalent weight 
as a posting to rec.humor.  That is, one really never knows if 
anything (i.e. the examples) in the Primer should be taken as 
fact (and thus copied).

Anyhow, for starters, the definition of rdfs:Datatype in the Vocab doc
seems too sparse.  What is the meaning of:

[[
rdfs:Datatype - represents those resources that are RDF datatypes.
]]

What is this class used for?  How does one implement support for this?
What is its relationship to the rdf:datatype attribute?

Concepts says:

[[
RDF provides no mechanism for defining new datatypes. XML Schema 
Datatypes [XML-SCHEMA2] provides an extensibility framework suitable 
for defining new datatypes for use in RDF.
]]

I think it would be very useful if a normative example or description
for doing the above was included.  

BTW, the links in [1] do lead to datatyping info but the primer's
Typed Literals section doesn't appear to include any of those links.

> What the WG has done is to define how to represent datatyped 
> values in RDF, 
> given there is a datatype meeting the constraints that RDF 
> imposes defined 
> somewhere.  One of the things we have not done is to provide an RDF 
> mechanism for defining new datatypes.
> So at present there is no mechanism to use rdfs:Datatype to 
> define new 
> datatypes nor to describe the lexical space of a datatype.

I wasn't able to parse the first sentence but if rdfs:Datatype
is not used to define datatypes (I can't imagine why I thought
it would be used for that purpose:-)), then the Vocab spec should 
clearly state that.

I'm looking for a normative (in-band) solution for two problems:

1. How to state a property's values may only contain a fixed set
 of strings.

2. How to state the values of a container may only contain
 strings from a fixed set.

I presmue #1 is addressed by defining an appropriate datatype using 
XML schema.  Is that correct?

I didn't see a solution for #2.  Do the new specs address this problem?

Thanks,

Art
---

[1] http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Nov/0527.html
Received on Tuesday, 3 December 2002 09:20:16 GMT

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