Re: XML Schemas: Best Practices

[Martin Bryan <mtbryan@sgml.u-net.com>]

> It would be nice if there was a way to explicitly flag places where
> extensibility may occur: "hey, instance documents may extend <Book> at
> this point, so be sure to write your code taking this possibility into
> account

The XML Schema spec deliberately takes the opposite approach. If a complex
type should not be extended it should be flagged with final="extension" (or
final="#all" if restrictions are forbidden too). Otherwise you must presume
that the type definition can be expanded. But remember that every time it is
expanded it must be given a new name, so there is not chance of a conflict
between a reference to the original name and a reference to the expanded
name. (I don't see where substitution groups make this any differrent, as
they have to refer to a specific model/element, and these models do not have
direct inheritence properties.)

Martin Bryan
The SGML Centre