[relax-ng-comment] Re: [relax-ng] Identity constraints

[James Clark <jjc@jclark.com>]

> > However, outside the database constituency, there did
> > seem to be a feeling that something lighter-weight than full XQuery was
> > needed.  I would summarize the desired level of functionality as a bit
more
> > than what's in XML Schema, but with a strong requirement that it must be
> > streamable.
>
> I don't understand how identity constraints can be streamable: you have
> to see the whole document before you know if the constraint is satisfied
> or not.

Streamable in the sense that you don't need to keep the whole document in
memory.

There's been quite a lot of work on streamable subsets of XPath, but it's
quite challenging from an implementation point of view.

James