XML validation

Rick Jelliffe ricko at allette.com.au
Fri May 14 19:03:54 BST 1999

 From: Bryan Cooper <bryan.cooper at veritas.com>

> In any case, what I feel is that its EASIER for me to setup an XML
> thang than what I see as a separate syntax in the DTD world

I am not particularly proposing a syntax: using semi-BNF things like XML
content models or putting them in element syntax wasnt my point. (And,
certainly, I am not
saying that validation needs to be done at the XML processor, which is
your other point.)

My point is there are lots of other structures in an XML document which
at the moment cannot be validated.  Newbies ask a predictable set of
questions: first "can I have required but in any order?" (e.g., SGML's
&), then "can I specify that if I have a size attribute you must also
specify a units attribute?".  And in SGML people wished there was a way
to constrain internal links to particular kinds of elements. I think
these would be useful and inexpensive forms of validation to have (I
think that was the point of your 50 lines of Python comment).

If we already have validator code that checks a DOM NodeList (the
element's contents), I don't know why it would be so difficult to have
validators to check the NamedNodeMaps (attributes), and to check what is
at the other end of  an IDREF (or even an XLink for that matter).  The
XML Schema:Structures draft seems too conservative in this area: if it
doesnt give substantial advantages over markup declarations I dont see
the point:  a little nicer improvement to content models for database
support and an enormous increase in size.

Rick Jelliffe

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