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[Bug 10882] New: [XQuery11] Why do external types introduced by external functions have to be subtypes of xs:anyAtomicType?

From: <bugzilla@jessica.w3.org>
Date: Thu, 30 Sep 2010 18:02:47 +0000
To: public-qt-comments@w3.org
Message-ID: <bug-10882-523@http.www.w3.org/Bugs/Public/>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=10882

           Summary: [XQuery11] Why do external types introduced by
                    external functions have to be subtypes of
                    xs:anyAtomicType?
           Product: XPath / XQuery / XSLT
           Version: Member-only Editors Drafts
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: XQuery 1.1
        AssignedTo: jonathan.robie@redhat.com
        ReportedBy: oliver@cbcl.co.uk
         QAContact: public-qt-comments@w3.org
             Group: XSLXQuery_WG


Section 4.18 states:

An XQuery implementation may augment the type system of [XQuery and XPath Data
Model (XDM) 1.1] with additional types that are designed to facilitate exchange
of data with host programming languages, or it may provide mechanisms for the
user to define such types. For example, a type might be provided that
encapsulates an object returned by an external function, such as an SQL
database connection. These additional types, if defined, are considered to be
derived by restriction from xs:anyAtomicType.

This should say the implementation can augment XDM with additional item types,
as I assume sequences of these types are also allowed.

I would also like to know why these types must be subtypes of xs:anyAtomicType,
and not just subtypes of item().

There are many expressions in XQuery that take arguments of type
xs:anyAtomicType and behaviours would have to be defined for these expressions.
  I guess most of the time the behaviour would be to raise an error.  If they
don't behave like atomic values, then maybe they shouldn't be atomic values.

For similar reasons that function items are not atomic values, atomic values
are a often a poor fit for new types introduced.

I would suggest changing the text to the following:

An XQuery implementation may augment the type system of [XQuery and XPath Data
Model (XDM) 1.1] with additional item types that are designed to facilitate
exchange of data with host programming languages, or it may provide mechanisms
for the user to define such types. For example, a type might be provided that
encapsulates an object returned by an external function, such as an SQL
database connection. These additional types, if defined, are considered to be
derived by restriction from xs:anyAtomicType or subtypes of item() (but not
node(), xs:anyAtomicType or function(*)).

I hate to say it but should these types not also be mentioned in the data
model?

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Received on Thursday, 30 September 2010 18:02:48 GMT

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