Re: xs:field selecting optional items

Erik,

My quick reading of the request suggests that it's similar to one of the 
issues the WG considered earlier. See [1]. The WG considered the request 
and decided that the spec is correct and the clauses do not need to 
change. The WG also observed that this issue is a source of confusion and 
wants to clarify it in a note. See [2].

Can you confirm that this is the same issue as the one you are raising?

Note that there are 2 steps involved in Identity Constraint validation.
1. Form the "key-sequence". In this step, it is indeed allowed for a 
"field" to match nothing. (Hence the key-sequence is incomplete.)
2. Verify the key-sequence. In this step, for "unique", it's OK to have 
incomplete key-sequence, but it's not OK for "key".

So there isn't a single answer to "are incomplete key-sequences allowed". 
It depends on the variety of the identity constraint.

[1] http://www.w3.org/Bugs/Public/show_bug.cgi?id=2543
[2] http://www.w3.org/Bugs/Public/show_bug.cgi?id=4202

Thanks,
Sandy Gao
XML Parser Development, IBM Canada
(1-905) 413-3255
sandygao@ca.ibm.com


www-xml-schema-comments-request@w3.org wrote on 2007-01-18 10:24:49 AM:

> 
> 
> 
> 
> hello.
> 
> i am proposing a clarification of the section about how identity 
> constraints are validated. when i look at section 3 of the validation 
> section http://www.w3.org/TR/xmlschema11-1/#d0e20523, i see the 
> following text:
> 
> "For each node in the ·target node set· all of the {fields}, with 
> that node as the context node, evaluate to either an empty node-set 
> or a node-set with exactly one member, which has a simple type."
> 
> i would say this clearly allows having fields selecting optional 
> items. maybe this could be made more explicit, however, because 
> implementations differ. eclipse accepts xs:field selecting an empty 
> node set, whereas other implementations complain about that (they 
> seem to assume that the selector of a field must always select a node).
> 
> maybe a note could make the spec easier to understand here.
> 
> cheers and kind regards.
> 
> erik wilde   tel:+1-510-6432253 - fax:+1-510-6425814
>         dret@berkeley.edu  -  http://dret.net/netdret
>         UC Berkeley - School of Information (iSchool)
> 
>