Semantics (was Re: Inheritance in XML [^*])
W. E. Perry
wperry at fiduciary.com
Fri Apr 24 00:45:34 BST 1998
Tim Bray wrote:
> 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
I agree with your clearly-conveyed preference to avoid endless discussion of what
the XML definition might have been. However, we can simply agree to do just that,
without impugning the usefulness of "semantic" for the core discussion of this
list. Elements, entities and attributes do have meaning: they are, precisely,
sememes. The fundamental work for which we have chosen XML as our tool is the
definition--either by empirical derivation or by prescription--of the sememic
content of the elements entities and attributes which populate our documents. It
is such definitions which we publish in XML by means of semantically significant
context. The specific forms of that contextuality and, by necessary implication,
the semantics which it serves are the very stuff defined by the XML standard. In
short, every instance of an XML tag is, precisely, a semanteme.
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