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Re: C.4 Undeclared entities?



At 2:30 PM 10/20/96, Charles F. Goldfarb wrote:
>O.K. "In nature" *was* a bit poetic, but my assertion is still true. However, I
>should clarify that by "DTD" I mean the abstraction called a "document type
>definition", not SGML's declarations that describe the portion of a DTD that
>SGML knows how to deal with. (Most SGML practitioners use "DTD" to mean what I
>called the "external subset" in my posting.)
   Your Platonic idealism is quaint, but the nominalists among us will
disagree. At any rate, these (putative) philosophical entities _need_ not
be addressed in the XML standard.


>In other words, every object is an instance of a class; therefore, every
>document is an instance of (at least one) class of documents, known as a
>"document type". A DTD is the description of the properties of members of that
>class.

There is an infinite set of such classes.

>That's true. I was referring to the DTD that most closely accounts for the
>particular instance. For want of a better term, let's call it the "maximally
>precise" DTD. For example, if an instance were:

>example deleted...

>The latter would be just one of an unbounded set of guesses, as you say. The
>former has the property that it describes this instance exactly, and no other.

To make a statement like this, you need to define a well-founded ordering
on DTDs, with the property that any set of DTDs has one and only one least
upper bound. You need to prove that these properties hold.

Once you have, then you can talk about _the_ minimal DTD. This is not a
case where handwaving will do.  A book on denotational semantics of
programming languages might clarify these issues.

>The maximally precise DTD is more real than the rest of them because it is the
>only one that can be justified. In the above example, we can't use p+ because
>there is no evidence that a "doc" exists with other than two "p"s in its
>content.

First you have to prove that such an object exists.

Pardon the philosophical note, but how else should one respond to
syntaxt-definition discussions where the mind of God plays a significant
role!

  -- David

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