Semantics (was Re: Inheritance in XML [^*])

[Tim Bray]

At 01:15 PM 4/23/98 -0400, 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. 

Well, we just have a difference of perception.  I think that
"element", "element type", "notation", and so on are profoundly
*syntactic* constructs.  I think an element is  a piece of an XML
document that is bounded by tags; an entity is a chunk of
text that is either provided literally or referred to via URL.  It
is true that the spec provides operational rather than purely grammatical
descriptions of some aspects of things, but that is largely for
convenience.  Dan Connolly has argued repeatedly and forcefully that
the spec could be completely re-written to avoid discussion of the
processor's actions (he is right) and that this would be an improvement
(I'm not convinced).

The fact that the XML processor has a couple of required *behaviors*,
most notably error handling, does not constitute anything like
what I think of in connection with the term "semantic".

I suppose you can argue that declaration in DTDs do have a semantic
of grammatical constraint.  OK, granted. 

But in the instance, Elements and attributes don't mean anything in and 
of themselves.  They doubtless have semantics that are used by humans and 
computer programs in particular application domains, but that's none of 
our business.

And finally... words are only of use in facilitating human 
communication when there is some shared understanding as to their
denotation and connotation.  The term "semantic", judged by this standard,
has clearly and empirically lost its usefulness in this discussion.

But of this I am confident: elements, attributes, and entities don't
mean anything in and of themselves. -Tim


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