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RE: Is xdt:anyAtomicType itself atomic?

From: Michael Rys <mrys@microsoft.com>
Date: Wed, 10 Nov 2004 14:48:35 -0800
Message-ID: <BAE415CEAA831548800F68C44E905AF5DD362B@RED-MSG-60.redmond.corp.microsoft.com>
To: "Paul J. Lucas" <plucas@bea.com>, <public-qt-comments@w3.org>

I don't think Mike and I disagree (see below for a clarification of my
sentence). There are two aspects to types in XQuery: Their position in
the type hierarchy with is determined by named typing and derivation
rules. In that case xdt:anyAtomicType lives between xs:anySimpleType and
above all the built-in primitive atomic types. It is considered the most
general atomic type and is abstract.

On the other hand, a type also has an extend that contains all instances
that can be considered an instance of that type. Since our type system
is polymorphic, an instance of a subtype is an instance of its
supertype. Thus the extend of instances that are considered instances of
xdt:anyAtomicType is the union of all the instances of its subtype. 

I hope this clarifies it. 

Best regards

> -----Original Message-----
> From: public-qt-comments-request@w3.org [mailto:public-qt-comments-
> request@w3.org] On Behalf Of Paul J. Lucas
> Sent: Wednesday, November 10, 2004 1:48 PM
> To: public-qt-comments@w3.org
> Subject: RE: Is xdt:anyAtomicType itself atomic?
> On Wed, 10 Nov 2004, Michael Kay wrote:
> > No, it's not defined as the union of all atomic types, it is defined
> the
> > supertype of all atomic types. It's the parent type of all atomic
> in
> > the same way as anySimpleType is the parent of all simple types ...
> 	According to the Formal Semantics, section 3.4.1, Predefined
> 	Types, xs:anySimpleType *is* defined as the union of all
> 	primitive atomic types and xdt:anyAtomicType *is* defined as
> 	the union of atomic types.
> 	My question was not about the definition of xdt:anyAtomicType
> 	since that is quite clearly defined as a union as cited above.
> 	My question was about what "atomic" means and whether
> 	xdt:anyAtomicType, as defined, is considered "atomic."
> On Tue, 9 Nov 2004, Michael Rys wrote:
> > XQuery's type system and the subtype hierarchy are based on named
> > A named union type in that system is defined as being a subtype of
> > xs:simpleType and not a subtype of xs:anyAtomicType. So in that
> > the type itself is not atomic.
> 	That, to me, quite clearly says that xdt:anyAtomicType is not
> 	itself atomic.

[Michael Rys] "the type itself" should read "the type T itself".

> 	It would be nice if the two of you agreed.
> 	- Paul
Received on Wednesday, 10 November 2004 22:49:08 UTC

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