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RE: /WD-xpath-datamodel-20030502/

From: Kay, Michael <Michael.Kay@softwareag.com>
Date: Wed, 21 May 2003 18:54:35 +0200
Message-ID: <DFF2AC9E3583D511A21F0008C7E62106073DCE63@daemsg02.software-ag.de>
To: Ashok Malhotra <ashokma@microsoft.com>, Norman Walsh <Norman.Walsh@Sun.COM>, "Kay, Michael" <Michael.Kay@softwareag.com>
Cc: David.Pawson@rnib.org.uk, public-qt-comments@w3.org

> We need to be careful here...
> 
> | We have added statements in the XPath and XSLT specifications saying
> | that the set of types may be extended by implementors, I think the 
> | Data Model document probably needs to say something to reflect this.
> 
> Users cannot create new primitive datatypes.

Users of XSLT 1.0 have indeed been able to create new primitive data types,
as part of the "extension function" mechanism. For example, an extension
function sql:dbConnect() can return an object of type "database connection".
The only thing you can do with such an object is pass it to another
extension function; but it's still useful. Of course such types can never
appear as the value of a node.

We have stated in the XSLT spec that the same capability is available in
XSLT 2.0, though the effect (like everything connected with extension
functions) is somewhat implementation-defined, and we are still debating
exactly how much we want to constrain it. Some people have suggested that
such "external objects" should be represented by an object within our type
system acting as a surrogate, for example an anyURI or a hexBinary; but this
seems unnecessarily clumsy.

Michael Kay


  All they can do 
> is restrict the existing 19 XML Schema primitive types. Since 
> the value space of a restricted type is a subset of the value 
> space of the primitive type (I'm only discussing atomic 
> types, not lists and unions
> here) the value space of atomic types cannot be extended by 
> users. Users can create new datatypes that cover some subset 
> of this value space.  
> 
> All the best, Ashok
> > -----Original Message-----
> > From: public-qt-comments-request@w3.org [mailto:public-qt-comments- 
> > request@w3.org] On Behalf Of Norman Walsh
> > Sent: Monday, May 19, 2003 1:41 PM
> > To: Kay, Michael
> > Cc: David.Pawson@rnib.org.uk; public-qt-comments@w3.org
> > Subject: Re: /WD-xpath-datamodel-20030502/
> > 
> > 
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > / "Kay, Michael" <Michael.Kay@softwareag.com> was heard to say:
> > |> From section 5.
> > |> quote.
> > |> The value space of the atomic values is the union of the value 
> > |> spaces of the nineteen primitive XML Schema types. unquote.
> > |>
> > |> Does this imply that no types (or at least atomic types) 
> from any 
> > |> other source are valid within this data model?
> > |>
> > |> Is this lockout for anything other than XML schema types or some 
> > |> direct derivation?
> > |>
> > |> Or more specifically, lockin to XML schema types?
> > |>
> > |
> > | We have added statements in the XPath and XSLT 
> specifications saying
> > that
> > | the set of types may be extended by implementors, I think the Data
> Model
> > | document probably needs to say something to reflect this.
> > 
> > Yes.
> > 
> >                                         Be seeing you,
> >                                           norm
> > 
> > - --
> > Norman.Walsh@Sun.COM    | Whatever you may be sure of, be sure of
> this:
> > XML Standards Architect | that you are dreadfully like 
> other Web Tech. 
> > and Standards | people.--James Russell Lowell Sun 
> Microsystems, Inc.  
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> 
Received on Wednesday, 21 May 2003 12:58:44 GMT

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