Path: utzoo!utgpu!water!watmath!watdragon!watsol!tbray
From: tbray@watsol.waterloo.edu (Tim Bray)
Newsgroups: comp.text
Subject: SGML defended (again)
Message-ID: <8049@watdragon.waterloo.edu>
Date: 28 Jul 88 13:43:04 GMT
Sender: daemon@watdragon.waterloo.edu
Reply-To: tbray@watsol.waterloo.edu (Tim Bray)
Distribution: world
Organization: U. of Waterloo, Ontario
Lines: 36

In article <61454@sun.uucp>, sears@sun.uucp (Daniel Sears) writes
>SGML provides rules for describing tag sets.  So let's create two very simple
>tag sets that we will assume are SGML conforming.  The first has two tags and
>the second has three.
>...
>it is possible to translate a document from the first tag set to the second.
>But it is not possible to translate a document from the second tag set to
>the first because there isn't an equivalent tag for <mark3>.  What SGML
>tries to guarantee is a way of describing the different tag sets, but it
>does not guarantee that the tag sets will be rich enough to hold all the
>objects that other tag sets may contain.

Uh, am I missing something?.  The second has more structural information
than the first.  Clearly you can't translate without 

1. Losing information, or
2. Passing the extra info through; maybe the text processor for the first
   example can be made to understand it.

If you want complete interchangability of documents, you need a general
agreement on all possible structural components of all documents.  This
is clearly impossible.  Not that we shouldn't try - the AAP effort is
worthwhile.

The next best thing is a standard, flexible, easily-parsed syntax for
marking up the structural components that do exist so that we maximize
our ability to translate them.  This is all SGML is.  But it's a *lot*
better than the alternative - parsing troff/TeX gibberish.

>In summary, the goal of structured document systems is
>quite laudable, but I think it is necessary to distinguish a system like
>SGML from that goal.
I'll buy that.  But for the time being, structural markup is the only
safe way to store text for which there may be unanticipated future uses.
This includes nearly all on-line text.
Tim Bray, New Oxford English Dictionary Project, U. of Waterloo