wd-xml-names: external dtd subsets (and external entities in general)

james anderson James.Anderson at mecomnet.de
Tue Aug 11 22:21:49 BST 1998

Tim Bray wrote:
> At 09:28 PM 8/11/98 +0200, james anderson wrote:
> >II. please establish a method to bind a prefix which covers the internal and
> >external dtd subsets.
> This was discussed by the WG and eventually voted down; the advantages
> of the attribute approach, combined with the desire to avoid having
> multiple ways to do the same thing, led to the PI approach being
> amputated.
> >without such a mechanism, the dtd's denotation is undefined.
> I don't understand what you mean by "denotation".  In general, the
> usefulness of your postings would be improved by more attention
> to the use of terminology, and where you need to use a new term
> (e.g. "extent" in your previous posting and "denotation" here) you
> should provide a definition for it.

re: scope and extent.

The terms are relevant since, as (I believe) Mr Durand has already noted, the
prefixes can be understood as variable bindings. In fact, it is possible to
implement them as dynamic variable bindings within the decoding process.

I work with Steele's definitions. (from his reference on common lisp)
He devotes chapter 3 to them. I believe it is online, but know, unfortunately
only of a location for the document in its entirety.
(http://www.cast.uni-linz.ac.at/st/vision/software/lisp.html) The concepts are
not his alone, but his is the reference which I have on my desk.

The following definitions are excerpted from the Common Lisp hyperspec
courtesy of Harlequin: (http://www.harlequin.com/education/books/HyperSpec)

extent n. the interval of time during which a reference to an object, a
binding, an exit point, a tag, a handler, a restart, or an
environment is defined. 

scope n. the structural or textual region of code in which references to an
object, a binding, an exit point, a tag, or an environment (usually
by name) can occur. 

They are not 100% adequate, as it is not clear how they apply to attribute
declarations, for which the "spatial or textual region" is unclear.

re: denotation.

In the process of implementing an XML processor, I have (defacto) produced an
operational semantics for XML. Whereby I am not alone, just explaining. One
"half" of the semantics is the XML encoding syntax. The other "half" is a
particular storage model (DOM-like) and a collection of operations on this
store. The last part is a specification for which operations on the store are
entailed by a given encoding. I have been using "denotation" to mean just
that: the effect of a document on the store. In the case of the dtd, it would
be the entity/element/notation/... declarations which it produces.

> >if, on the other hand, such a mechanism is provided, then validation is
> >possible on the basis of namespace-aware 1.0 conformant dtd's.
> Only trivially so.  As I have pointed out, the hard part is not matching
> up the names, it's making compound DTDs.  I have also pointed out how
> a mechanical instance/DTD rewrite could address some of the issues
> of namespace-aware validation.  I have not suggested a solutoin for
> how to solve the *hard* problem, namely how to go about making a
> compound DTD, and would like to hear input on that. -Tim

In my case, the storage model restricts all stored names to be universal
names. That is, all character sequences, which appear at a point in the
encoded stream which the syntax specifies as a name, are required to denote a
universal name in the store. If this requirement is met, then it is possible
to automate the rewrite process which you described in your earlier post.
(Please look back through the recent posts; you will note a response from me
on this topic). If, on the other hand, said sequences do not denote an
universal name, then the result of the decoding is undefined, since given that
the names have no denotations (ie. they identify no name in the store), loosly
speaking, the DTD also has none.

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