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   Re: Syntax and semantics

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  • From: "W. E. Perry" <wperry@fiduciary.com>
  • To: xml-dev@xml.org
  • Date: Tue, 16 May 2000 18:49:38 -0400

Paul Prescod wrote:

> Can we move our syntax/semantics discussion to xml-dev? If you will
> resend your message I will respond to it there.

-------- Original Message --------
Subject: Re: Syntax and semantics
Resent-Date: Tue, 16 May 2000 16:53:38 -0400 (EDT)
Resent-From: xml-uri@w3.org
Date: Tue, 16 May 2000 16:53:33 -0400
From: "W. E. Perry" <wperry@fiduciary.com>
Organization: Fiduciary Automation
To: Paul Prescod <paul@prescod.net>, xml-uri@w3.org
References: <00bd01bfbe73$e7296730$a60a1712@col.w3.org>
<39205454.B26BD786@fiduciary.com> <392193A8.242955BE@prescod.net>

Paul Prescod wrote:

> A few questions:

Exactly the right questions!

>  * can you define semantics?

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. The two views are actually not that far apart,
if you accept my
opinion that in both of them it is a function, a process (see
below on
behavior) which
elaborates semantics from syntax.

>  * In what sense does XML not have semantics?

The specification of XML 1.0 stays admirably focussed on
delineating the
syntax. With few
exceptions (and in my reading most of those are to support
features and SGML
compatability--most notably the DTD itself), the spec avoids
various of the
syntactically permissible possibilities to the expression of

> 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
certainly is. Nothing in
the XML 1.0 spec mandates a canonical infoset or a tree structure.
As I
have argued at length
elsewhere, imposing either the infoset or the tree structure view
XML syntax, as
specified, greatly and gratuitously curtails the expressive and
functional possibilities
inherent in the syntax alone.

> Can any useful language,
> or meta-language, or meta-meta-language be entirely devoid of

As your example above indicates, there will always be some small
content in the
choice of, for example, less-than symbols rather than curly
braces, or
ampersands rather than
hashmarks. Those choices can be limited to the minimum logistic
requirements of orthography,
particularly when a syntactical specification is restrained, or
on assigning them any
significance beyond the orthographic. (de minimis non curat

>  * 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

> If they write a web browser that archives
> any link you click on and play's music for bold, will you defend them
> the basis that semantics are local?

No. If I want that behavior I will buy their software or use their
process (or to use Tim
Bray's terminology, dispatch to it from my local node).

> I think that behavior is local, but
> semantics absolutely must be shared.

Not shared a priori. That is the single great lesson to be drawn
from the
Internet topology
of autonomous, largely anonymous nodes which, when they act must
one another as peers
because they do not know enough about each other to infer any
relationship. Semantics
are effectively negotiated in the instance, and the ability of two
to negotiate a
successful transaction, understanding, or other disposition of
content on one occasion
implies NOTHING about their likelihood of reaching a similar
or any conclusion at
all, with analogous content on a subsequent occasion (this really
is a
Heraclitan cosmos).
The vertical industry data vocabularies (FpML, ESteel, etc., etc.)
have been the
shining demonstration of XML's acceptance in the past year are
on a closed-world
view which is anathema to the real potential of XML as syntax. All
these vocabularies are
designed to convey intent, with the expectation that intent will
correctly interpreted and
result in the execution of a desired process. It is only in a
world (a cartel, to put
it bluntly) that those expected processes could be assumed to be
generally known and
generally considered desirable activities. In the Internet
topology we
simply do not have
enough knowledge of our fellow nodes to make such assumptions, but
we may
well have the
desire to do business with or otherwise communicate with them. In
to do so, we could
first attempt to indoctrinate them in the shared assumptions and
premises of our own
milieu, but that might not work:  they may prove recalcitrant; it
turn out they are more
influential than we within the larger Internet universe; or they
simply not give us their
attention, or understand what we are trying to communicate. 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
elaborate on this
process now; I have done it at plenty length elsewhere. The only
point to
make now is that
the negotiation must be based on each node handed the other
neutral content. If
the receiver can do something useful with the content received,
then by
definition it has an
interest (expressible through process) in that message; otherwise,
does not and cannot be
compelled to except  (to the extent both sender and receiver are
and willing) by
serially providing it the pieces from which it can build, in its
context, the ability to
perform some useful process upon particular instance content.

> But behavior and semantics are
> separate. You can read the Catcher in the Rye and start a fund for
> wayward teens or decide to shoot John Lennon.

Precisely! Semantics are the outcome of, or more exactly are
in, the behavior
applied to syntactically understood content.

> > In an Internet topology, the effective definition of a
> > process is the form of its execution at a particular occasion on a >
'client-side' ....

> You speak of behavior and semantics as if they are interchangable. I
> don't feel that they are.

No. Semantics are elaborated from syntax through process


Walter Perry

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