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- From: "Rick Jelliffe" <firstname.lastname@example.org>
- To: "Paul Prescod" <email@example.com>, <firstname.lastname@example.org>
- Date: Mon, 24 Nov 1997 16:21:14 +1100
> From: Paul Prescod <email@example.com>
> "Sometimes the actual claims for markup-based systems are overstated;
> the claim that SGML results in portable documents, for example,
> falls afoul of the observation that it is possible to put angle
> brackets around troff tags, supply a simple document type descrip-
> tor,and thereby achieve anSGML-compliant document, without gaining
> any portability or descriptiveness for the information. True
> portability requires not only that informa- tion be transportable
> from one machine to another,but that the semantics of that informa-
> tion be the same on either machine. SGML, in particular,claims to
> transfer no semantics, so it surely cannot guarantee portability."
>  "Markup Reconsidered" http://www.sil.org/sgml/raymmark.ps
Without wishing to disagree in any way with Paul, the quote is perhaps not
quite true, I think.
Sticking angle brackets on troff code may give you a document that is
syntactically *valid* SGML but, because to the extent that it uses elements
to markup processing instructions, the document does not *conform* to
SGML. Such conformance cannot be judged mechanically, but by looking at the
definitions in ISO 8879 for processing instructions and elements.
People often seem to think "SGML is a grammar; I can markup all sorts of
sloppy things; therefore SGML is a bad grammar". But SGML is more than
a queer grammar, it is a language: the terms "element" and
"processing instruction" (etc) have broad but useable meanings.
I think one problem with XML is that these definitions of what an element,
etc., actually mean are not present. XML *is* just a grammar, more or less.
But to convert it to a useful language, we often have to plug in SGML's
And again, we shouldn't then think that in all cases "SGML conformance=good;
SGML non-conformance=bad". But that is separate from "do I need
SGML validity? do I need XML well-formedness? do I need a custom syntax?".
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