XSchema Spec Section 2.4, Draft 2

francis francis at redrice.com
Fri Jun 26 16:14:53 BST 1998

John Cowan wrote:
> Chris Maden wrote:
> > <XSC:AttDef Name="one-of-these" Type="IDRef" Required="Yes"
> > Enumeration="index biblio gloss"/>
> >
> > You can't do that with DTDs.  The value for one-of-these must be
> > specified, and it must be a legitimate IDREF, but it is constrained to
> > one of the specific IDs listed.
> Forgive me, but I find this particular instance incomprehensible.
> Why would you want to refer to only one of a specific set of IDs?

Is this the SGML v. DP culture gap in action? I spend my days building
GUI screens to constrain input to hard-coded sets of IDs (radio buttons)
or variable sets of IDs (combo-box, list box), partly so that I can
guarantee the input will fit into databases which, in turn, compete for
business on the power of their referential integrity support. 

This is key DP usability we're discussing here - in fact my reaction was
"hey, there's a nice comprehensible example!"

Admittedly I would have fleshed it out a bit - 

<XSC:AttDef Name="OrderNo" Type="IDRef" Required="Yes"
Enumeration="Order00234 Order00235 Order00237"/>
<XSC:AttDef Name="PartNo" Type="IDRef" Required="Yes"
Enumeration="Widget Sprogget Fluggit"/>

I'm still no expert on XML, but am I right in thinking that using only
DTDs there would be no way of declaring that OrderNo may be "Order00234"
but may not be "Widget", while PartNo may be "Sprogget" but may not be

I suspect that another DP type concern will be the extent to which the
schema can be interpreted reliably at build time - when the design
decisions are being made and agreed - as opposed to at run time, when
the internal subset and parameter entities are instantiated...

=[More Snips]=


Francis Norton

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