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RE: LC-93 disjoint datatypes

From: Vun Kannon, David <dvunkannon@kpmg.com>
Date: Tue, 10 Oct 2000 12:13:29 -0400
Message-Id: <1BFA1EA02439D21193A20008C7A4B20F04F65A2A@USMNYEXC04>
To: "'C. M. Sperberg-McQueen'" <cmsmcq@acm.org>
Cc: W3C XML Schema Comments list <www-xml-schema-comments@w3.org>
Thank you. At first blush, the new proposal does satisfy my basic request.
I'm unsure how the union of types across different schemas will look, but I
have to admit to not having read the new spec carefully. I'm envisioning a
situation in which one schema defines 
colorsA={red,yellow,green}
, a second schema defines 
colorsB= first:colorsA union {pink,blue}
eventually, an instance of a third schema containing
attribute name="currentColor" type="schema2:colorsB"
has
<trafficLight currentColor="schema2:pink"/>
but if the color was green what is the attribute value? schema1:green or
schema2:green?

Have I created a union with the type or the set of values the type
aggregates? I hope that question makes sense.
Thanks,
David vun Kannon

> -----Original Message-----
> From: C. M. Sperberg-McQueen [mailto:cmsmcq@acm.org]
> Sent: Monday, October 09, 2000 10:01 PM
> To: Vun Kannon, David
> Cc: W3C XML Schema Comments list
> Subject: LC-93 disjoint datatypes
> 
> 
> Dear Mr. Van Kunnon:
> 
> The W3C XML Schema Working Group has spent the last several months
> working through the comments received from the public on the last-call
> draft of the XML Schema specification.  We thank you for the comments
> you made on our specification during our last-call comment period, and
> want to make sure you know that all comments received during the
> last-call comment period have been recorded in our last-call issues
> list (http://www.w3.org/2000/05/12-xmlschema-lcissues).
> 
> Among other issues, you raised the point registered as issue LC93,
> which suggests that XML Schema be modified to make it possible to
> build a simple datatype out of other simple datatypes with disjoint
> lexical spaces.
> 
> Ashok Malhotra replied in May that this is not possible (and indeed
> it was not possible at that time).
> 
> More recently, however, after discussion of the issue you raised, in
> conjunction with related issues raised by others, the WG agreed to
> adopt a proposal to allow simple types to be constructed as the union
> of other simple types.  There is no requirement that the lexical
> spaces be disjoint: the value passed is tried against each member type
> in turn, and the first one it matches is the one which applies.  (This
> means that A union B will not behave in exactly the same way as B
> union A, so schema authors are urged to exercise caution.)  This means
> that it is possible to create union types for (for example) (a)
> anything from this enumeration of strings, or (b) any string.  The
> xsi:type attribute may be used in the instance as a discriminator to
> force the value to be associated with a particular member type.
> 
> It would be helpful to us to know whether you are satisfied with the
> decision taken by the WG on this issue, or wish your dissent from the
> WG's decision to be recorded for consideration by the Director of
> the W3C.
> 
> with best regards,
> 
> -C. M. Sperberg-McQueen
>   World Wide Web Consortium
>   Co-chair, W3C XML Schema WG
> 
> 
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Received on Tuesday, 10 October 2000 12:13:52 GMT

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