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Re: Defaulted values and identity_constraint checking

From: David Beech <David.Beech@oracle.com>
Date: Thu, 04 Jan 2001 11:37:56 -0800
Message-ID: <3A54D114.360ED16D@oracle.com>
To: "Henry S. Thompson" <ht@cogsci.ed.ac.uk>
CC: Noah_Mendelsohn@lotus.com, www-xml-schema-comments@w3.org
Oracle's interpretation was to apply the defaults first, as likely
to be most useful and intuitive.

For a key, the utility is small - you can only use a default once
within the scope of the key, otherwise you don't have a unique key.

But for a keyref, it could conceivably be useful to have a default 
like "catchall" that refers to an element with a "catchall" key.

As for the intuition, I personally tend to think of attribute
and element defaults as a front-end shorthand - it's just as though
you had explicitly written the defaults in place in the instance.
Are there situations in which that intuition is faulty?



"Henry S. Thompson" wrote:
> Noah_Mendelsohn@lotus.com writes:
> > Just want to confirm: my reading of [1] is that defaulted attribute and
> > element values do not participate in identity_constraint checking.  As far
> > as I can tell, identity constraint checking operates on the unaugmented
> > infoset, right?
> >
> > [1]
> > http://www.w3.org/TR/xmlschema-1/#Identity-constraint_Definition_details
> Sigh.  This is underspecified in the current spec., so I guess people
> could read it either way.  I'm not terribly happy with either reading,
> myself.
> ht
> --
>   Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
>           W3C Fellow 1999--2001, part-time member of W3C Team
>      2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
>             Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
>                      URL: http://www.ltg.ed.ac.uk/~ht/
Received on Thursday, 4 January 2001 14:41:14 UTC

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