RE: [xml-dev] XML spec and XSD

["Michael Kay" <mike@saxonica.com>]

>    Saying that something like, xs:redefine isn't implemented 
> consistently across different XSD processors, IMHO doesn't 
> justify condemning XSD completely. I think, even a correct 
> implementation of say, xs:redefine on one or two processors 
> is good enough. 

In the case of xs:redefine the problem is that the spec is underspecified,
so two implementations can do different things and both be consistent with
the spec: it's not the case that some of the implementations are
"incorrect". This is certainly one of the many technical weaknesses of the
XSD specification. It was of course an attempt to reproduce one of the ways
in which DTDs are used to define variant and customised content models.
Henry Thompson has produced some guidelines for use of xs:redefine which, if
you follow them, will give you interoperable behaviour and will probably
meet the requirement.

I would expect good experienced knowledgeable people like Tim Bray and Rick
Jelliffe to say "There are many weaknesses in XSD and we know today how many
of these things could have been done better" - which is perfectly true. I
would not expect them to say "XSD is a complete failure". I simply don't
think one can say that of a technology which is so widely and successfully
deployed, and which has some technical characteristics (notable the
attribution of types to elements and attributes) which are currently unique
to that technology.

Regards,

Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay