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Re: XPath 1.5? (was RE: typing and markup)

• To: michael.h.kay@n...
• Subject: Re: XPath 1.5? (was RE: typing and markup)
• From: Uche Ogbuji <uche.ogbuji@f...>
• Date: Tue, 07 May 2002 15:49:54 -0600
• Cc: "'Ian Fitchet'" <ian.fitchet@l...>, xml-dev@l...
• In-reply-to: Message from "Michael Kay" <michael.h.kay@n...> of "Tue, 07 May 2002 19:10:58 BST." <000a01c1f5f2$8ac45d20$6501a8c0@pcukmka>
• Sender: uche.ogbuji@f...

> >  From which follows, what does 7/5/2002 mean to you?  Either we share
> >  some (date) context that it means 7th of May or it means July 5th.
> >  It doesn't matter how you represent it so long as we both know how to
> >  interpret it.
> >
> >  Is there any means of indicating non-W3C types?
> >
> Sure, you can define a type called american-date as a restriction of
> xsd:string, constrained by a regular expression, and you can then define
> functions that convert an american-date to an xsd:date and you can then use
> standard XQuery functions and operators to do arithmetic on them. No
> problem. (Except that you'll confuse European recipients, but we're used to
> that).

This is what I mean t by paltry extension facilities.  You cannot type irrational numbers by regular expression, to take an example.

The problem is that for all things for which regex happens to work, you do get decent support in the 2nd generation of XML specs.

But you fall off a very precipitous cliff just by the accident of needing a data type that cannot be defined by regular expression.

As a system designer, this is what I call a fatally brittle system.

By allowing constraint systems to be *layered* upon XML in an orderly manner (I'd have no problem with the favorite data types of the XSDL folks being one of these possible layers), then you have a much less brittle, and IMHO far more useful system, overall.


-- 
Uche Ogbuji                                    Fourthought, Inc.
http://uche.ogbuji.net    http://4Suite.org    http://fourthought.com
Track chair, XML/Web Services One (San Jose, Boston): http://www.xmlconference.com/
DAML Reference - http://www.xml.com/pub/a/2002/05/01/damlref.html
RDF Query using Versa - http://www-106.ibm.com/developerworks/xml/library/x-think10/index.html
XML, The Model Driven Architecture, and RDF @ XML Europe - http://www.xmleurope.com/2002/kttrack.asp#themodel

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