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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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