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All of these problems don't matter as much if all you are designing is a validation language. They mainly become problematic when you want to perform operations on these types either in a programming or query language.
________________________________
From: Michael Kay [mailto:michael.h.kay@ntlworld.com]
Sent: Fri 10/10/2003 9:13 AM
To: Dare Obasanjo; 'Eric van der Vlist'; xml-dev@lists.xml.org
Subject: RE: [xml-dev] fundamental facets - inquiry from the XML SchemaWorking Group
I think it would be quite feasible to define a system that allowed
pluggable primitive types. It should be quite possible to describe a
type as an object supporting a particular IDL interface, and allow
implementors to map this IDL interface to concrete programming language
bindings.
I'm not sure it's true that The problems that "The XQuery working group
has already had a painful time dealing with the fact that ... not enough
emphasis was placed on defining operations on these types just
validation. The problems are different:
* some of the types aren't well-enough defined (e.g. anyURI, which
doesn't say what the mapping is between the lexical space and the value
space)
* some of them have context-sensitive lexical representations (QName,
NOTATION)
* the type hierarchy is badly thought out (e.g. no supertype for
numerics, anyURI not being a subtype of string).
* the equality operation (based on identity in the value space) is too
rigid for a query language: you want to be able to treat two values as
equal without losing the distinctions between them, e.g. the number of
trailing zeros in a decimal
* the date/time/duration types just occupy an absurdly large proportion
of the space
* base64 and binHex are two different lexical representations of the
same values
I don't think many of the problems are directly to do with operations
being underspecified. It's just a badly designed and poorly specified
set of not-very-primitive types. A much smaller set with better
extensibility mechanisms would have served us all far better.
Michael Kay
> -----Original Message-----
> From: Dare Obasanjo [mailto:dareo@microsoft.com]
> Sent: 10 October 2003 16:21
> To: Eric van der Vlist; xml-dev@lists.xml.org
> Subject: RE: [xml-dev] fundamental facets - inquiry from the
> XML SchemaWorking Group
>
>
> Really, and what spec would define how you perform operations
> on these types? The XQuery working group has already had a
> painful time dealing with the fact that when the W3C XML
> Schema working group created their type system not enough
> emphasis was placed on defining operations on these types
> just validation.
>
> The ability to add your own primitive types seems to make
> sense for validation but puts a significant burden on
> technologies that depend on W3C XML Schema such as XQuery.
>
> ________________________________
>
> From: Eric van der Vlist [mailto:vdv@dyomedea.com]
> Sent: Fri 10/10/2003 6:52 AM
> To: xml-dev@lists.xml.org
> Subject: Re: [xml-dev] fundamental facets - inquiry from the
> XML SchemaWorking Group
>
>
>
>
> To make it short, can't we take this opportunity to build a
> datatype system in which people could add their own primitive types?
>
> Eric
> --
> See you in Philadelphia for XML 2003.
>
> http://www.xmlconference.org/xmlusa/
> Upcoming schema
> tutorial:
> - Philadelphia (7/12/2003)
> http://makeashorterlink.com/?V28612FC5
> Tutoriel XSLT:
> -
> Paris (25/11/2003) http://makeashorterlink.com/?L2C623FC5
> --------------------------------------------------------------
> ----------
> Eric van der Vlist http://xmlfr.org
> http://dyomedea.com
> (W3C) XML Schema ISBN:0-596-00252-1
> http://oreilly.com/catalog/xmlschema
> --------------------------------------------------------------
> ----------
>
>
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