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RE: Attribute groups

From: Snow, Corey <CSNOW@ddpwa.com>
Date: Fri, 15 Mar 2002 11:28:03 -0800
Message-ID: <200203151928.g2FJS4q23855@thumper.deltadentalwa.org>
To: "'Jeni Tennison'" <jeni@jenitennison.com>
Cc: "'xmlschema-dev@w3.org'" <xmlschema-dev@w3.org>
> 
> Hi Corey,

Hi Jeni- thanks for your reply.

> > 
> What you're describing is a "co-occurrence constraint" in which the
> presence of one attribute affects whether the presence of another
> attribute is allowed.
> 
> XML Schema is notoriously bad at co-occurrence constraints. The usual
> advice in this situation would be to do one of the following:

Well, at least I'm not running into a problem that I should have been able
to resolve quickly or easily. :)

> 
>   - Express the distinct attribute combinations as separate complex
>     types both derived from the same abstract complex type; make the
>     element have the abstract type as its type; use the xsi:type
>     attribute to identify which of the two types is being used in the
>     particular instance. (Note that this involves changing the look of
>     your XML instance documents.)
> 

This is expressly what I was trying to avoid, unfortunately. I was hoping
not to have to modify the instance documents too much. However, since this
is to support a content-management system, I can probably come up with a
simple markup that I can transform to the appropriate markup so as to avoid
confusing my users with esoteric XML attributes. :)

Here's another question for you, then- is it possible, using abstract types
and/or elements, to create a "polymorphic" element? 

>   - Express as much as you can in XML Schema, then use Schematron or
>     another schema adjunct to express the co-occurrence constraint.
> 

I've been hearing a lot about Schematron, so I think I need to look into it.
I've never played with it much. I know that there's some information on it
in "Professional XML Schemas", which I have a copy of, so I'll start there.

Regards,

Corey Snow

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Received on Friday, 15 March 2002 14:28:36 GMT

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