[SCL] Fwd: Common Logic status with respect to standards

Mon Nov 3 20:08:26 CST 2003

pat hayes wrote:
>> pat hayes wrote:
>> [...]
>>
>>> Murray, can you suggest how best to render SCL into XML? I think what 
>>> we should aim at here is not so much a fully-fledged XML user syntax, 
>>> so much as a way to take (almost) any SCL concrete language and 
>>> convey it down an XML pipe, so that the original form can be 
>>> extracted at the other end with minimal work using XML tools as far 
>>> as possible to 'parse' the XML. This thinks of XML as a way to convey 
>>> other syntactic forms between computers, rather than as a markup 
>>> language; but still it seems to me to be a reasonable goal.
>>
>> Any codified XML syntax is by definition a markup language, and from
>> your request I can't see exactly what you'd want that would be different
>> from what I think of as a markup language.
> 
> I may have mis-spoke: forgive me. What I meant to say was that it would 
> not itself be a language in its own right, in the sense that, say, 
> RDF/XML is a language, but rather that it would be a system of markup 
> which would facilitate the exchange of other languages (the SCL concrete 
> syntaxes). Perhaps this is trivial (?), although the issues you raised 
> about for example connecting content from several documents still seem 
> to be relevant. Also, do you have any thoughts on how to include SCL (or 
> indeed anything else) inside XHTML without causing browsers to display 
> the SCL? (If that last question is completely off the wall, ignore it.)

I don't think it's off the wall at all. As you may know, I created a
mechanism for the XHTML DTD by which it's possible to design composite
syntaxes. This can also be done in RELAXNG and XML Schema. Now, getting
something to be valid XML/XHTML is one thing, getting it to work in
browsers is another. The problem is when you try to define "browser".
Which browser, which version, which platform? Et cetera. Reliably, there's
no way to do it across all browsers. There are some that can handle
embedded non-XHTML markup, but I wouldn't say they're in the majority,
and some of them don't do it right. You could embed the XCL in comments,
but XML processors are allowed to throw out comments so you wouldn't
even see the XCL in the resultant parse tree.

So the short answer is really no. There may be ways to trick a browser
by only including empty elements, which wouldnt' be displayed, but
that would profoundly alter and limit what you could do with the syntax.
(Everything would be in an attribute value, and you couldn't have
elements containing elements -- it'd be ugly.)

>> If the document at
>>
>>      http://cl.tamu.edu/docs/scl/scl-latest.html
>>
>> is the latest, if all you want is (from what I can tell) what you say,
>> they the section "A XML DTD for SCL" already has what you want. As to
>> how that matches up with the abstract syntax, I have no idea. Nor
>> could I unless I understood SCL better, which is one of the reasons
>> why you can't act in some mechanized way in designing markup languages.
>> If you want something as simplistic as what's in the SCL document, you've
>> already got it.
> 
> Well, maybe that is all we need for the present, then.

If you have no interest in URIs or interoperability across the web,
that's all you'd need.

[...]
> Let me try to put the point in the form of a question. The SCL abstract 
> syntax allows many different concrete syntaxes to exist with the same 
> abstract form. So for example we might have a piece of textbook-logic 
> with infix connectives and relational atoms indicated like R(a,b) and 
> R(b,c), and names being character strings without whitespace. Or, we 
> might have a postfix Post-style notation in which this would be written 
> as abRbcR&; or a graphical CG-style notation, or whatever. Think of all 
> of these encoded as text in various documents: could there be a single 
> way to mark these all up in XML so that they all exhibit the same 
> abstract SCL structure on their sleeve, as it were?

I think that if the syntaxes were all each defined in a EBNF grammar
and you fed those specs to an engineer, you'd have in a week a set
of translators between the concrete syntaxes. There are even automatic
parser generators that take EBNF in, and generate a parser*. With XML,
you already have the wide availability of parsers of course. But all
of these are isomorphic, syntax-level distinctions. The meaning of
all is the same, as you want it to be. There may be some things that
the XML can express that can't be handled by the KIF or CG-style
syntax, not because of semantics, but because of things like linking
and document structure, which as you say in a message I'm just reading,
the XML is operating at a different level, at the entity/resource
level.

Murray

http://www.antlr.org/
......................................................................
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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