Re: Issue: overlapping with XML Schema Part 2

[James Clark <jjc@jclark.com>]

> TREX overlaps with XML Schema part 2.  If we assume that XML Schema Part 2
is
> THE datatype system, such overlapping should be avoided.  If we plan to
make
> a new datatype spec or provide a subset of XML Schema Part 2, such
overlapping
> is probably acceptable.

I strongly believe we should *not* tie ourselves to XML Schema Part 2.
Schema Part 2 has a number of separable aspects:

a) the repertoire of primitive types
b) derivation by restriction and the repertoire of facets
c) derivation by union
d) derivation by list
e) the concrete syntax for representing all of the above

In the long run, I think I would want probably a subset of a) and b).  I
view the anonymous datatypes mechanism in TREX at the moment as a stop-gap.

As for c), I don't think derivation by union should be in the datatype
system.  Putting it in the datatype system forces you to have two ways to do
essentially the same thing. Note that XML Schema Formal Description (aka
MSL) uses the same mechanism to represent choice amongst datatypes and
choice amongst complex types.  I think d) is similar, though less clear-cut.

As for e), the syntax used by XML Schema is pretty sucky (at least to my
taste) (lots of useless simpleType elements), and in any case fits poorly
with the rest of our syntax.

I certainly don't think XML Schema Part 2 is the one true datatype system.
It has many very poorly defined features, and many features of highly
marginal utility.  I also think the whole idea of there being one system of
datatypes that suits all users is broken.  Different domains will need
different systems of datatypes.  Many document applications can get by with
a very, very simple set of datatypes.

James