Re: [xml-dev] XML spec and XSD

[David Carlisle <davidc@nag.co.uk>]

> I am really not sure, why entities are not allowed to be defined in
> XSD. I believe, there is some design principle behind that, and also
> the XML Schema WG must be aware about this issue I believe.

essentially for the same reason that XSD should not be referenced from
the xml spec. XSD (like Relax NG, XSLT etc) all work on the infoset
produced by parsing an XML document, thus they require an XML parser to
provide them input, to expand entities etc.

DTD processing on the other hand does not work by taking an infoset as
input but is instead a modified parser that reports validation outcomes.

XSD can not define entities as it is too late in the chain. If the
document uses entity references that are not defined to the parser then
the document is in error (or not well formed if there is no external DTD
reference at all).

David

________________________________________________________________________
The Numerical Algorithms Group Ltd is a company registered in England
and Wales with company number 1249803. The registered office is:
Wilkinson House, Jordan Hill Road, Oxford OX2 8DR, United Kingdom.

This e-mail has been scanned for all viruses by Star. The service is
powered by MessageLabs. 
________________________________________________________________________