[Bug 13399] [XP 3.0] Constraints on Unions in SequenceType

http://www.w3.org/Bugs/Public/show_bug.cgi?id=13399

--- Comment #2 from Michael Kay <mike@saxonica.com> 2011-07-31 19:53:37 UTC ---
Looking at this again, bug #12626 reminds me that it may be unwise to use the
phrase "whose member types..." without qualification.

Also, to align fully with "Schema Component Constraint: Type Derivation OK
(Simple)", we should allow unions that are derived from other unions by a
trivial restriction (one that involves no constraining facets) - this case
isn't very important, but we might as well handle it the same way that XSD 1.1
does.

Revised formulation: 

<quote>
the type named by an _AtomicOrUnionType_ must either be an atomic type, or an
*unrestricted union type*. An *unrestricted union type* is a type whose
{variety} is _union_, whose {facets} property is empty, and whose {member type
definitions} consists exclusively of atomic types and *unrestricted union
types*. 

Note: the definition of *unrestricted union type* excludes union types derived
by non-trivial restriction from other union types, as well as union types that
include list types in their membership. Unrestricted union types have the
property that every instance of an atomic type defined as one of the member
types of the union is also a valid instance of the union type.
</quote>

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Received on Sunday, 31 July 2011 19:53:42 UTC