[SCL] Representing constraints that go beyond EBNF

[Murray Altheim]

John F. Sowa wrote:
 > Murray,
 >
 > I'm glad that we agree on many of the most important issues.
 > What you tell me about those people makes me feel better
 > about them, and if we find ourselves working with them
 > at some point, I would be happy to do so.

A number of these people have done a lot of "volunteer" work,
on unpaid standards work, open source, free documentation, etc.
And some of them might very well be interested in SCL, so I
think it's just good policy to consider them as potential allies.
There's no point in scratching the litter box their way.

 > In any case, the main point I wanted to make is that we can
 > adopt the practice of defining a language in itself.  That
 > is done in the ISO standard for Z, which uses Z to define Z.
 > Following are the steps:
 >
 >   1. EBNF, by itself, cannot state the context-sensitive
 >      constraints that associate bound variables with their
 >      defining points (i.e., quantifiers or declarations).

Understood.

 >   2. EBNF can be defined as a concrete syntax for a subset of
 >      FOL (or SCL).  I recommend that we include a section in
 >      the proposed standard that defines ISO EBNF as a concrete
 >      syntax for a subset of SCL.  (This would be a normative
 >      section that would also serve as an illustration of how
 >      SCL can be used to define the semantics of a language.)

Agreed. Would that specific subset have a name? A particular
domain of usability? Or would it simply be a subset because
it was the part of SCL that was defineable via EBNF?

 >   3. Those parts of the syntax and semantics that need greater
 >      expressive power than EBNF can be stated in any of the
 >      concrete languages defined in the document (KIF, CGIF,
 >      or traditional infix notation for predicate calculus).

Because neither KIF nor CGIF are standards, I would think probably
the infix notation for predicate calculus would be best, even
though it's not a standard. (?) If at some point KIF becomes an
ANSI or ISO standard we could reconsider and write an Annex.

 >   4. Therefore, we can use two concrete languages for defining
 >      the syntax and semantics of SCL:  EBNF for the context-free
 >      constraints on SCL syntax, and KIF for the model-theoretic
 >      semantics and for the context-sensitive constraints on the
 >      syntax.
 >
 >   5. The combination of KIF and EBNF would constitute a complete
 >      formal definition of SCL in SCL conformant languages.

Substituting a standardized or at least traditional constraint
language on the rest, this sounds like a plan.

 > Instead of using KIF as the defining language, we could use any
 > other concrete notation, such as traditional infix notation. That
 > would have the advantage of using two already well established
 > languages:  EBNF and traditional predicate calculus.

Yes. As above.

 > In fact, we could make the Z people feel happy by defining Z as an
 > SCL conformant language, and then using Z as the supplement to EBNF.
 > That would have the advantage of (1) bringing Z into the SCL fold and
 > (2) honoring the ISO slogan of "Buiding standards on other standards."

I don't think standards are really about making other standards happy.
If there's some agenda to bringing the SCL and Z work together, that
should probably be taken up as a separate standards activity under the
same aegis as this work, but after we're finished. If you haven't
burned out Harry during the first phase, then tackle it. But getting
just SCL finished is plenty of work.

 > John
 >
 > PS: The criticism "don't know logic" isn't the only one I throw around.
 > I have also run into many people designing languages who don't have
 > a clue about the difference between a regular grammar, a context-free
 > grammar, or a context-sensitive grammar.  That doesn't make them
 > stupid, but it often leads them to design kludges.

I think you also have to realize that (a) people use different
terminology than you do if they come from a different domain, and
(b) people's expertise is often not in what you think it is, even
based upon their ostensible qualifications and background. Mine is
a case in point. While I can't exactly explain what my expertise
is (!), it's not in filmmaking, my BA. DocBook was developed by a
guy with an advanced degree in ancient Arabic history, HyTime by
somebody trying to figure out how to describe musical notation.
And there are certainly some mathematicians and logicians who'd
be better off as gardeners. They may "know logic" but they are
woefully inadequate as communicators, socially inept and unable
to explain themselves or their ideas to others. And they as well
as anyone can design kludges. I worked with faculty on a university
campus for nine years, and the mathematics professors were the
worst communicators of any department. Good design doesn't come
about simply because of expertise in a given field, it comes from
being able to elucidate ideas clearly and concisely. It's what
I see as a difficulty here: you guys think you know exactly what
SCL is, but you're having a heck of a time with the communication
part. Complex things are hard to describe, it goes with the
territory. I don't mean to pick on mathematicians particularly;
this is true of all people, all fields.

I just think it's not a good policy to deride people you don't
know very well, as sometimes the reasons they're doing what they're
doing are not clear from the outside, and you might find that they
are actually allies in the struggle, not enemies.

Murray

...........................................................................
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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