[SCL] Approach to a concrete syntax

[Murray Altheim]

Tanel Tammet wrote:
 > Murray Altheim wrote:
 >
 >> I suppose it's less interesting because there is less understanding
 >> now that the issues of markup have hit the table.
 >
 >
 > In a way, yes: I'd like to avoid putting too much stress on the
 > markup issues right now. Not that they are unimportant, though.
 >
 >> I think you're missing my point: in expressing SCL in RDF you have no
 >> ability to avoid the complexities.
 >
 >
 > I do completely agree to what you say here. What I was saying is that
 > we have several issues at hand (*) complexity issue, where I'd like to
 > avoid covering all possible the problems which may appear (*) RDF issue.
 > I do NOT think that RDF issue simplifies things (that is why I did
 > not initially try to make SCL-in-XML RDF-compatible). IMHO both the
 > complexity issue and the RDF issue have to be taken seriously.
 >
 > Even more: since attempts for RDF compatibility (whatever this will mean)
 > will by nature bring additional potential complexities, we should then be
 > ESPECIALLY careful to avoid going into all the rising actual and
 > potential complexities.

I think we're on the same page, or should I say, in the same room.

In going from the strict, model-theoretic semantics of SCL into an
expression in XML, we're altering the form of expression from use
of the commonly-used expressions of FOL (such as upside down As and
backward Es) to an expression in XML markup, constituting an XML
markup language. This in SGML parlance would be called "an application
of SGML". It is a strict syntax that has a direct relationship with
the semantics it embodies.

When we express character data in a computer system we use a specific
character set. In XML this is Unicode/ISO 10646. The character set
for XML includes the characters used in expressions of classical
FOL, such as ∀ (upside down "A" if your emailer doesn't display
this correctly) and ∃ (backwards "E"). I believe it would be
possible in SGML (but not in XML) to design an SGML application
that could actually use these characters directly as markup
characters, and I think it'd even be possible to express FOL in
SGML without alteration. There could be a few hitches, point is,
SGML doesn't require you to use angle brackets. These can be altered
in the SGML declaration.

The entire set of "characters" are actually termed "glyphs" in
Unicode*, owing to their absence of interpretation. They're just
abstract symbols with no meaning whatsoever, absent interpretation
in a given context. They're not even "characters" yet!

An expression of "classical" FOL is a form of markup, expressing
the formal, model-theoretical semantics of FOL using an accepted
lexical notation.

What I believe we can do with XML is treat that minimally. I'll
endeavour to fix up Chris' draft as promised, and also alter my
XCL Level 1 syntax to match his as closely as possible, with the
minor alterations I've proposed to Pat, and which are already
there but not as clear as could be. Then, following on from Level
1 is XCL Level 2, a lexically-different but semantically
identical XML markup language. The only difference between Level
1 and 2 in practice is that the latter is web-enabled, and may
form the basis of other forms of logic *without* requiring new
syntax. And any alterations in syntax will *hopefully* be with
only very minor changes. I can envision an extension that would
express the situational calculus with only a few small changes.
Now, I don't claim to be a mathematician, but I'm pretty sure I
can pull this off. I do understand that Pat has little interest
in that, which is fine. I have little interest in the details of
the logic itself. I'm trying to meet him halfway.

Murray

* BTW, if you want to express these as characters in XHTML/HTML
documents, you can use the character entities defined in XHTML,
which are shown in

     http://kmi.open.ac.uk/projects/ceryle/doc/docs/NOTE-charents.html

......................................................................
Murray Altheim                  <http://kmi.open.ac.uk/people/murray/>
Knowledge Media Institute
The Open University, Milton Keynes, Bucks, MK7 6AA, UK

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