Semantics (was Re: Inheritance in XML [^*])
greyno at mcs.com
Fri Apr 24 06:37:38 BST 1998
Paul Prescod wrote:
> If XML had no semantics, then XSL, XLL and the DOM would have to
> explicitly describe the mapping from syntactic features to the abstract
> nodes that they work on. But they do not, because XML has semantic
> concepts like "element, "element type", "notation" and "attribute" that
> are *described by* the syntax.
Some questions/comments. I find your posts wonderful food for thought,
but I'm not always sure I understand them. And be advised I don't do
smileys, prefering the challenge of conveying wit and humor in English
(much harder and funner than coding), but I don't always win my battles
with the language, so please be a generous reader. So, regarding the
Replace "element", "element type", "notation", etc, with "foo", "bar",
"baz", etc. Do you still have semantics? The English words used by the
spec happen to have commonly understood "meanings" which, to my eye,
color the discussion in unfortunate ways. And what exactly is the
semantics of "semantic concepts like ... that are *described by* the
syntax"? Isn't that begging the question a little bit?
> Here's what a language with no semantics looks like:
> a -> b"q"c
> a -> ca
> b -> "d"
> c -> "e"
> Even given a parse tree, you can't do anything interesting with this
> language, because it has no semantics.
"Colorless green ideas sleep furiously." Chomsky, late 50s or
thereabouts. Adj adj n v adv.
English has semantics. The quoted sentence has syntax, not semantics.
Syntactically it's unremarkable. Semantically, it's pretty cool, but
meaningless (in the ordinary sense of meaningless; in context it's
profoundly meaningful, and even out of context it's not bad: try it out
on somebody at your next cocktail party.) The fact that we can describe
the sentence with "parts of speech" tags doesn't render it
"meaningful". (Linguists: I'm vaguely aware that Chomsky's assertions
about the fundamental difference between syntax and semantics has been
challenged. True? Relevant?) Am I missing your point, Paul?
The text of the spec may have stuff regarding *how* things are supposed
to work, but the syntax of it looks to me to be completely devoid of
implication. Unless, that is, one gets really abstract and declares,
"Oh! your language has structure! Therefore it carries some sort of
implicit meaning, reflecting your Weltanshauung, not mine! Down with
the oppressor!" (Sorry, got carried away. But the similarity with late
(political) Chomsky is striking all the same.)
So I'm left wondering why we don't have formal definition for all this
stuff. The editors of the standard look like a pretty impressive bunch,
which leaves me all the more mystified as to why prose instead of a
formal language. (I have in front of me a copy of "The Definition of
Standard ML, of which I can make neither heads nor tails - but it looks
*very* rigorous and formal.) Look at DSSSL: a wonderful, even
beautiful, work of the imagination, written in . . . legalese? Do we
really need "shall" in a technical spec?
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