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   Re: [xml-dev] can you use inheritance (extension) in relax ng?

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Gustaf Liljegren wrote:
> At 06:54 2003-10-25 -0700, Dare Obasanjo wrote:
>>As a document validation language RNG is simpler, more
>>expressive and less verbose than W3C XML Schema. As a
>>datayping language W3C XML Schema is the only game in
>>town [...]
> Can you (or someone else) elaborate on this? I don't understand what
> features are missing från RNG as a "datatyping language" (what's that?). It
> has the existing datatypes from WXS, it has the ability to construct regex
> patterns, it has named patterns for complex types. What's not there?

RNG doesn't have type derivation. You can parameterize an existing type 
but you can't define a new named type based on an existing one.

RNG doesn't have "complex types" at all. One might argue that nothing is 
better than XML Schema's faux-OOP extension types, but a case could be 
made for named patterns. Some think it handy in a query language to 
know, e.g., that all arguments to a function match a certain pattern. 
(Some don't.)

More subtly, RNG is designed for validation, not type assignment. 
Because RNG patterns are closed under union, it can easily happen that a 
given sequence is valid according to more than one pattern, and there is 
no decision procedure to choose which pattern to use in assigning a 
type. XML Schema resolves such issues by a "first match" rule for its 
union (simple) types and by disallowing ambiguity in complex types.

> I think the day Microsoft turns to RNG will be a lucky day for XML.

Amen to that.

Bob Foster

> Gustaf
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