Re: How to specify validation properties in DTDs?

Chris Maden (crism@ora.com)
Tue, 24 Mar 1998 10:18:45 -0500

[Parik Rao]
> Hi, I'm trying to figure out how do I do parameter validation in my
> DTD. For example, I have an element which specifies a SIZE as an
> attribute. I'd like to enforce certain rules : the charaacter data
> in size is digits and the size is always less than 1,000,000 (for
> example). As far as I can figure out, there is no way to do this!
> E.g.
>
> <ATTLIST MYELEMENT
> SIZE CDATA #REQUIRED
> >
>
> Well, how do I set validation parameters for size? I tried to play
> around with entity but really couldn't come up with anything:
>
> <!ENTITY % NUMBERONLY ...now I'm stuck>
> <!ATTLIST MYELEMENT SIZE %NUMBERONLY;>
>
> Anyone done this sort of thing? Is this sort of validation beyond
> the scope of DTDs?

On the nose: this is beyond the scope of DTDs.

This kind of restriction must be specified as an application
restriction, and enforced by means outside the current scope of XML.
A stylesheet might be able to check the attribute value, and throw an
error if it doesn't conform (if the XSL WG decides to have error
handling); an XML application could check this information after the
parser parses the data.

There's also work ongoing about XML-Data, which would permit you to
specify restrictions like this. However, it's not done (or close, I
think).

-Chris

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