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XQuery and RDF datatypes was: RDF specifications

From: Jonathan Borden <jborden@mediaone.net>
Date: Tue, 4 Dec 2001 17:16:52 -0500
Message-ID: <01f701c17d11$6140fe90$0a2e249b@nemc.org>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: <www-rdf-interest@w3.org>
Peter F. Patel-Schneider wrote:

> In fact, the XQuery Data Model supports precisely this interface, or
> so I gather from my reading of the specification.

Perhaps you mean the XQuery 1.0 Formal Semantics (XQFS)
http://www.w3.org/TR/query-semantics/ ? Or XML Schema Formal Description
(XSFD) http://www.w3.org/TR/xmlschema-formal/ ?

both are currently WD and are intended to _supercede_ XML Schema 1.0
datatypes (just so we are clear about what we are discussing :-)

I thought we were discussing XML Schema datatypes, if you are instead
talking XQuery algebra then I couldn't agree more on that value of
incorporating this into RDF for several reasons (read on).

>
> > This is my entire point, even though it is quite apparent that two types
are
> > equal (their instance sets are identical), discovery of such type
> > equivalence is not necessarily possible by a type system that uses
> > _hierarchy alone_ in determining type algebra operations i.e. are two
types
> > equal, supersets or subsets. An _explicit_ type heirarchy tells you this
> > "because I say so", but more generally a type formalism allows such type
> > equivalences to be computed from the equations that define the types
> > themselves.
>
> Sure, and so you need access to an implementation of XML Schema datatypes,
> such as will be (or is) provided by an implementation of the XQuery Data
> Model.

Ok, this is much what I am saying, that RDF datatypes ought be aware of XML
in a 'formal way'. XDuce and XSFD are similar (as is the RELAXNG formal
semantics
http://www.oasis-open.org/committees/relax-ng/spec-20011203.html#data-model)
,
and XQFS builds upon this. Let me point out the open issue with operators
for simple datatypes: http://www.w3.org/TR/query-semantics/#Issue-0056
because is largely what the above discussion boils down to.

My statement was that XML Schema 1.0 datatypes was not itself sufficient,
which is precisely why XSFD and XQFS are necessary.

>
> My stance is quite simple.
>
> 1/ RDF should incorporate XML Schema datatypes.

I am not sure how RDF can 'incorporate' XML Schema datatypes alone. Do you
mean that the RDF DT semantics should incorporate XSFD and/or XQFS? Or do
you mean that RDF should incorporate the concepts of 'string' 'integer' and
'date'?

>
> 2/ The XQuery data model provides a relatively easy interface to get the
>    resultant typed literals into RDF.

yes! I strongly agree. Not only that but Jonathan Robie has shown me a
_terrific_ example using XQuery on XML/RDF datasets -- yet one more reason
why RDF++ ought keep close to XML++. XQuery is one of the most promising
technologies I've seen come out of these efforts.

>
> 3/ If semantic typing is needed, it can be done using a slightly modified
>    version of the code in an implementation of the XQuery data model.
>    (Basically, you need direct access to the part of the implementation
>    that performs the lexical-to-value mapping for XML Schema datatypes.)

Careful, because there are known inconsistencies between XML Schema _1.0_
and XSFD as well as XQFS (this is much of the _reason_ they were developed
_after_ XML Schema 1.0 was specified). Hopefully the work of XSFD/XQFS will
be incorporated into XSD 1.1.

A dizzying array of specifications isn't it?

Jonathan Borden (who is told interesting things at meetings about XQuery
because he is frequently mistaken for Jonathan Robie, and who can spell XML
Query Formal Semantics, but has no idea what it all means :-)
Received on Tuesday, 4 December 2001 17:17:17 GMT

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