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   Re: Syntax and semantics

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  • From: Paul Prescod <paul@prescod.net>
  • To: xml-dev@xml.org
  • Date: Wed, 17 May 2000 11:50:04 -0500

"W. E. Perry" wrote:
> ...
> In the terms of late 20th century critical theory:  that
> signified; or more fully, the body of content which is the 
> product of the signifier's inherent function. In Aristotelian 
> terms: the substance or stuff of meaning, beyond the mere 
> arrangement (syntattica) of its expression. 

I'll take that as "no"? Here are the sort of definitions that I can

An alphabet is a set.
A character is a member of an alphabet.
A string is a list of characters.
An XML document is a string that meets the following constrants: ...

> >  * In what sense does XML not have semantics?
> The specification of XML 1.0 stays admirably focussed on
> delineating the syntax. 

Actually, it mixes syntax and semantics shamelessly and inconsistently.
Stating here that "a processor must pass this to the application" and in
other places nothing at all.

> > Isn't the interpretation
> > of less-than symbols and ampersands as an annotated, tree-structured,
> > information set the "semantic content" of XML?
> As an 'information set' (and most especially as the Infoset) it
> most certainly is. Nothing in > the XML 1.0 spec mandates a 
> canonical infoset or a tree structure.

No, but that's just a bug. Some have proposed that the infoset,
namespaces and XML 1.0 be rolled into XML 1.1.

> As I have argued at length elsewhere, imposing either the infoset 
> or the tree structure view upon XML syntax, as specified, greatly 
> and gratuitously curtails the expressive and functional 
> possibilities inherent in the syntax alone.

Greatly, yes. Gratuitously, no. Similarly, mposing the XML syntax on
Unicode greatly curtails the expressive functionality of Unicode alone.
But in both cases *the whole point* is to reach into the universe of
possibilities and pick out the ones we are interested in. XML is not
interested in languages that cannot be expressed in XML syntax and is
just as uninteresed in concepts/data models that cannot be expressed as
(perhaps shallow) trees.

Let's talk about what happens if we don't have the infoset, both in
reality and in practice. In reality we have the problem that people do
not know whether this:

<![CDATA[]]><![CDATA[ ]]> 

is one text node or two.

In theory, things could get much, much worse were it not for our SGML
heritage keeping us sane. Some applications could start to treat
attribute ordering as significant. Some applications could start to
treat the distinction between ('') and ("") strings as significant. Some
could start treating the whitespace between attributes as signficant.
(If you use a tab here, it means X. If you use a space here, it means Y.
If you use two tabs here, it means Z).

Remember that the goal is not to maximize expressive paper but rather to
maximize *interoperability* and code reuse.

> >  * if semantics are entirely local, then does Microsoft have the right
> > to interpet the "a" element type in xhtml as meaning "archive" and the
> > "b" as meaning "Beethoven"?
> Absolutely, if they can implement desirable behavior from a
> process by so
> assuming.

I see. So you feel that the XHTML specification could be just element
types, with no description of either meaning or behavior. And then when
we send an XHTML document to a browser, the client and server could
somehow negotiate the meanings of the tags? I do not follow.

> That is where the value of the Semantic Web becomes apparent. One 
> pair at a time, autonomous nodes can build the semantic
> context within which they come to understand one another. I will
> not elaborate on this process now; I have done it at plenty 
> length elsewhere. 

#1. Can you provide a reference?

#2. What do we do while we wait for the Semantic Web?

#3. How can the Semantic Web ever be complete until computers are
artificially intelligence?

Consider: I have a purchase order database. The computer has no
knowledge of what that means. It is just a database with fields. You
send me a purchase order in an random vocabulary. I have no
foreknowledge of the vocabulary or its semantics. The document must be
sliced and diced so that it may go into my database. How can this be
done without a human intervenor? How can the computer know that your
company_name is what is in my database known as customer_name?

My experience is that semantic mapping is a process that takes place in
front of white boards, around meeting tables and occasionally in bars.

> The only point to make now is that the negotiation must be based 
> on each node handed the other semantically neutral content. 

Isn't the phrase "semantically neutral content" oxymoronic? I cannot
pick up Les Miserables and start reading. First I learn French. I need
the semantics behind the individual words to get the meaning of the
whole thing! And I need those semantics before I can read the book.

 Paul Prescod  - ISOGEN Consulting Engineer speaking for himself
"Hardly anything more unwelcome can befall a scientific writer than 
having the foundations of his edifice shaken after the work is 
finished.  I have been placed in this position by a letter from 
Mr. Bertrand Russell..." 
 - Frege, Appendix of Basic Laws of Arithmetic (of Russell's Paradox)

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