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SV: Union types derived by restriction

From: Bryan Rasmussen <brs@itst.dk>
Date: Mon, 20 Sep 2004 11:47:54 +0200
Message-ID: <2292448FDD501C4594181CA35CBA172003B821BE@its42.itst.local>
To: 'Michael Kay' <mhk@mhk.me.uk>
Cc: xmlschema-dev@w3.org

I don't know if somethings up with your mailer, mine or the list, but I've
now received 10+ copies of this mail. I guess we'll see with this if it's
the list. 

-----Oprindelig meddelelse-----
Fra: Michael Kay [mailto:mhk@mhk.me.uk]
Sendt: 20. september 2004 11:40
Til: xmlschema-dev@w3.org
Emne: Union types derived by restriction 



In Schema Part 1 (PER 18 Mar 2004), section 3.14.6, Schema Component
Constraint: Derivation Valid (Restriction, Simple), is the rule:

3.3.2.3 The {member type definitions}, in order, must be validly derived
from the corresponding type definitions in the {base type definition}'s
{member type definitions} given the empty set, as defined in ...

However, I'm having trouble seeing how one can define a union as a
restriction of another union in which the member type definitions differ in
any way from those of the base type definition. <xs:restriction> only allows
me to change the pattern and enumeration facets, not the member types.

For example:

(a) if the base type is a union of decimal and string, can I make the
derived type be a union of integer and string? Unless I'm missing something,
I think not.

(b) if the base type is a union of dateTime, date, and time, can I make the
derived type be a union of dateTime and date? Again, I think not.

So what does rule 3.3.2.3 mean? My suspicion is that it is vacuous.

Michael Kay
Received on Monday, 20 September 2004 09:59:03 UTC

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