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> > 1) Adding new value members to the value space of a type
> can't be any good
> > under any circumstances. It's possible to think up some
> use for such a
> > feature, but it would no doubt be better implemented using
> one of the other
> > mechanisms.
>
> If you mean simple type == datatype, then not only is it bad,
> it's not
> possible using W3C XML Schema. There is no derivation by extension
> from simple types.
I think that's the intent, anyway. I may be misremembering, but I thought
there was a loophole or ambiguity in the spec that might allow one to add
new enumeration values through simple type restriction? In any case it's
bad, bad,bad.
> Note here that W3C XML Schema extension is _always_ sequenced, in the
> sense that any member of a type defined by extension _must_ contain a
> member of the base type as a prefix.
What you're saying is that base members come before extended members? That's
fine, and it's not possible to extend (A, B, C[3]) with (A, B, C[3], C*) in
XML Schema, although it is possible to extend it to (A, B, C[3], D, C*).
It's that last case that I consider Not So Bad, but Paul seems to find
objectionable.
> This property does _not_ hold for substitution groups, where
> type-based patterns rather than element-based ones are the only safe
> way to go.
Not quite following you here, sorry.
>
> > 2) "Content space" refers to all specified child elements
> and attributes in
> > a type definition (there's probably a term for this
> already, but I've a
> > peasouper of mental fog today). The big fork in the road
> here is whether the
> > model group of elements is sequenced or not.
> >
> > 2a) If it's unsequenced, then addition (via extension) of
> new elements that
> > were restricted in occurrence in the supertype would likely
> break the bank.
> > For sequenced content, it seems less of a worry, taking
> Paul's XSLT example
> > as a worse case. Frankly, if you're not blocking extension
> of sequenced
> > content, you have to accept what you're given. Does that
> take too much
> > discipline? I'm the wrong person to ask, but a schema
> editor might support
> > an autoblocking configuration for complextype extension.
>
> Note here that W3C XML Schema extension is _always_ sequenced, in the
> sense that any member of a type defined by extension _must_ contain a
> member of the base type as a prefix.
>
> This property does _not_ hold for substitution groups, where
> type-based patterns rather than element-based ones are the only safe
> way to go.
>
> ht
> --
> Henry S. Thompson, HCRC Language Technology Group,
> University of Edinburgh
> W3C Fellow 1999--2002, 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/
> [mail really from me _always_ has this .sig -- mail without
> it is forged spam]
>
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