Re: [relax-ng] Control of the combinations of patterns

[Eric van der Vlist <vdv@dyomedea.com>]

On Fri, 2003-01-03 at 12:32, James Clark wrote:
> 
> > I allow grammars which will include this one to combine this definition
> > by choice or interleave while if I write:
> >
> > foo = &bar
> >
> > I forbid combinations by choice and if I write
> >
> > foo = |bar
> >
> > I forbid combinations by interleave.
> 
> This doesn't seem very useful to me. If you forbid this, then I can instead
> completely override the definitions instead of using combine.  In the
> context of RELAX NG, this sort of thing is at most a hint to users that want
> to customize a schema, 

Yes, exactly. And in any case, even with the strictest mechanism you
can't prevent people to edit a local copy of the schema or to use
another schema :-) ...

> and, as such, I think some conventional annotation
> attributes would be enough: eg an annotation attribute on a define that says
> whether is/is not intended to be combined with choice/interleave.

Agreed. You can then be more specific in which redefinitions should be
avoided to be compatible with such and such application.

> > Questions:
> >  - would it be useful to be able to forbid both (similar to the notion
> > of "final" definition)?
> > - would it be usefull to impose that a combination is applied (notion of
> > "abstract" definition)?
> 
> You can get something very similar to an abstract definition by using
> notAllowed.  For example, in the original schema use:
> 
> a = notAllowed
> 
> Then in the overriding schema use:
> 
> a |= element ....

This is similar but works only in the case where you don't provide any
original content for the named pattern "a", not if you want to define a
content which must be combined with something else.

Thanks

Eric
-- 
Freelance consulting and training.
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Eric van der Vlist       http://xmlfr.org            http://dyomedea.com
(W3C) XML Schema ISBN:0-596-00252-1 http://oreilly.com/catalog/xmlschema
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