Re: [xml-dev] DTDs, W3C Schemas, RELAX NG, Schematron?

[John Cowan <jcowan@reutershealth.com>]

Eddie Robertsson scripsit:

> See comments below.

Thanks for the review.

> > 5) RNG allows a (simple) datatype to be restricted not only by facet,
> > but by explicit extension and exception.  One can write 'xsd:integer -
> > "0"' to mean a nonzero integer (although unfortunately "00" will still
> > validate), or 'xsd:integer | "Inf" | "+Inf" | "-Inf"' when a value may
> > be integral or infinite.
> 
> This can quite easily be done using union types in XML Schema

I see that.  -1 for me.

> or if you want to
> restrict an integer type you can use the various facets provided for this.

But restrictions by facet are only pre-set ones.  You can restrict
an integer to be between -5 and +5, but you can't restrict a token,
say, not to be "foo".  Whereas in RNG that is just xsd:token - "foo".

> > 11) RNG lists consist of non-whitespace separated by whitespace, and the
> > non-whitespace need not be all of the same (simple) type.  A pattern like
> > "list {xsd:integer, xsd:string}+" is perfectly valid, and matches content
> > like "2 foo 5 bar".
> 
> This can be done by creating a list type from a union type in XML Schema.

True.  I didn't word this sharply enough.  If you want a list consisting
of alternating numbers and strings, RNG can do that but XSD can't:
a list type created from a union type is "list {(xsd:integer|xsd:string}+}",
and matches things like "2 5 foo bar".

> > What does RNG lack?  Mainly, it has no notion of keys or other identity
> > constraints, except for DTD-compatible ID and IDREF(S).  RNG validators
> > also don't provide any sort of PSVI, and indeed only a subset of legal
> > RNG schemas would be able to produce type tags at all (validity is always
> > decidable, but just *which* rule(s) were applicable may not always be).
> 
> What about default values?

Right.  I was lumping that with the PSVI under the heading of
infoset augmentations.  I will mention it explicitly in the next version.

-- 
John Cowan <jcowan@reutershealth.com>     http://www.reutershealth.com
I amar prestar aen, han mathon ne nen,    http://www.ccil.org/~cowan
han mathon ne chae, a han noston ne 'wilith.  --Galadriel, _LOTR:FOTR_