Entities in XSchema

John Cowan cowan at locke.ccil.org
Tue Jun 9 22:20:45 BST 1998

Paul Prescod wrote:

> SAX provides information on ID/IDREF attributes, but I don't think that
> ESIS did, so this is more debatable.

But not all SAX-compliant parsers do: attribute type checking is a
validity constraint only, so non-validating parsers are free to
return CDATA as the type of all attributes.

As one who is fairly SGML-ignorant, I would like to know:  Just what
is in the ESIS?  (If you will, limit the answer to things XML also
> Anyhow, I wouldn't care much if we cut loose all of those types. I just
> don't think that removing them is the natural extension of not checking
> text entities.

I was attempting to adopt the distinction between "what IS so" and
"what MUST BE so" (which DTDs conflate) and see where it led.
Content models say what must be so, and entity declarations say
what is so, that much is clear.  Attribute declarations are
a mixture.
> We might not need fixed attributes. A fixed attribute is merely an
> attribute with a single choice. Can't that be represented directly as a
> choice attribute with a single choice (yes, this implies that we would
> open up "choice" attributes beyond names...any arguments with that?)
> So that would allow us to reduce the "optionality" requirement to
> "optional or required".

Okay, that leads to a model with the following (meta-)attributes
of attributes:

	syntax (name | nmtoken | names | nmtokens | general) #IMPLIED
	choices CDATA #IMPLIED  -- a list of choices or "free" if none --
	optionality: (optional | required) "optional"
John Cowan	http://www.ccil.org/~cowan		cowan at ccil.org
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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