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[Bug 6513] [XQuery] inconsistent terminology in definition of derives-from()

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Date: Sun, 27 Sep 2009 21:59:58 +0000
To: public-qt-comments@w3.org
Message-Id: <E1Ms1mg-0005VH-8f@wiggum.w3.org>

--- Comment #18 from Michael Kay <mike@saxonica.com>  2009-09-27 21:59:58 ---
I believe a better approach to solving this problem would be along the
following lines:

Some of the rules for SequenceType matching require determining whether a given
schema type encountered as a type annotation in an instance document is the
same as or derived from an expected schema type. 

This determination is done by reference to a schema S (that is, a set of schema
components). This schema S is the union of:

(1) the in-scope schema definitions in the static context of the query module

(2) the schema used for validating the instance document

(3) potentially, further schema components that have been made available to the
processor in an implementation-dependent way.

A type error [err:XPTY0004] *may* [or *must*?] be raised if this union does not
constitute a valid schema (for example, if there are conflicts between types
present in the static context and types used dynamically for validating

We can then reduce the definition of derives-from to:

# derives-from(AT, ET) raises a type error [err:XPTY0004] if either AT or ET is
not present in S
# derives-from(AT, ET) returns true AT and ET are both present in S, and if one
or more of the following three conditions is true:

   1. AT is the same type as ET 
   2. AT is derived by restriction or extension from ET
   3. S contains some schema type IT such that derives-from(IT, ET) and
derives-from(AT, IT) are true.
# Otherwise, derives-from(AT, ET) returns false

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Received on Sunday, 27 September 2009 22:00:06 UTC

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