[SCL] Re: Report on Common Logic
Murray Altheim
m.altheim at open.ac.uk
Mon Nov 3 20:24:16 CST 2003
[pat, it would be helpful if you or your email software include who wrote
what you're responding to, so we can better keep track.]
|
pat hayes wrote: |
> Tanel Tammet wrote: <----
>> Hence, the nice stuff Murray was thinking about for
>> the XML syntax should be in our report also for
>> the ABSTRACT syntax, or not at all.
>
> Well, two points.
> 1. If this really is true, then in the short term I think we should say,
> not at all. BUT..
> 2. Im not sure that this really is the case. For example, there is
> nothing in the SCL logic to suggest that XCL might not have facilities
> for combining SCL content from several distinct documents. SCL does not
> concern itself with documents or refer to entire ontologies, and we
> could legitimately regard this for example as meta-logical in a strong
> sense.
>
>> The way do to this is to reserve some function
>> and predicate symbols in SCL full, plus have
>> strings in SCL full.
>
> We certainly need strings, but there is a delicate distinction between
> character strings and the 'abstract' thingies in the SCL AS.
Yes, they're operating at two distinct levels.
>> Then we would have a capability in syntax to
>> somehow express in semantics that
>> something like
>>
>> URL(STRING("http://www.w3c.org"))
>>
>> is an URL, whatever this means (I see no
>> other way to give meaning for such things
>> than to say that there is simply a subset of strings,
>> which is called URL-s, without saying anything about
>> how these URL-s etc are used).
>
> Well, an abstract syntax could distinguish URIs from the character
> string that encodes them, although that would not be sanctioned by RFC
> 2396 and I know would be controversial. Your function then is FROM
> strings TO URls, right? If you identify them then you don't need a
> function. (BTW, I don't think we need STRING either: we can just allow
> direct quoting in a concrete syntax.)
I wouldn't recommend having URIs and URIs-as-Strings. But it's certainly
a good idea to have Strings and URIs (or what I think are still called
"URI references" -- it changes about every week or so.). You will need
"String" when you get to designing concrete syntaxes, as you'll need a
small number of datatypes as matters of constraint on the markup language.
>>>> Web Enabled:
>>>> 1. Do we want XCL documents to be able to refer to other XCL
>>>> documents over the web? This would be how modules could be used
>>>> to construct larger statements/formulae/ontologies/etc.
>>>
>>>
>>>
>>> If this can be managed easily, yes. I think there is only a need to
>>> do this at the 'top level', ie for one ontology to consist of several
>>> XCL documents. One way to do this would be to include a kind of
>>> 'importing' mechanism, meaning: include all the SCL axioms from that
>>> document in here.
>>>
>>> I think it would be good if XCL could be mixed with other content in
>>> an XML document without that affecting the SCL content.
I think there's a certain fallacy that says you can put any kind of
communication within a wrapper of another kind of communication, and
that they're insulated from each other. The interpretation of each will
be altered by that embedding. Now, we can design something that allows
you to embed XCL within XHTML (or SVG, or...), but the interpretation
of the resulting document is not really within our control, only that
of the XCL fragment.
>> I agree. But this should be ANOTHER layer, not the
>> SCL layer, which does this.
>
> Agreed: I was assuming that XCL was involved with issues like this in
> the 'layer above'. After all, XML is in some strong sense *about* the
> business of encoding structure in documents and putting together textual
> entities into assemblies of one kind or another (is that fair, Murray?)
Yes. Whether you consider that a layer above or below, it's operating
at the layer of entities, resources, documents, etc. In DocBook you
can for example declare a series of entities for the chapters of a
book, and "build" the book from a series of transcluded chapters:
<!DOCBOOK book "-//OASIS//DTD DocBook 4.1//EN" "docbook.dtd"[
<!ENTITY chap1 SYSTEM "chapter1.xml">
<!ENTITY chap2 SYSTEM "chapter1.xml">
<!ENTITY chap3 SYSTEM "chapter1.xml">
]>
<book>
&chap1;
&chap2;
&chap3;
</book>
and this is functionally/semantically identical to having one big
document with everything in one file.
Now, there's entities and there's linking. XML allows by default
the former. The latter we'd have to design in, either using XLink
or by designing our own syntax. There's advantages to both.
>> For example (to go to extremes) we will not make SCL
>> "http-enabled" and start describing http issues
>> in the SCL spec.
>>
>> Ie, it is http-enabled without any efforts from our
>> side :-)
>
> I agree, but still would like Murray to think about issues like this,
> which I know can get very delicate and will eventually (soon?) be
> important in a deployed standard.
As you're probably guessing, I'm not very delicate. I think we can
safely ignore everything outside of the purview of an XML markup
language. If we want to get too far into the muck that the W3C has
raked up, I really will bow out in disinterest. It's not worth the
pain.
>>>> 3. are there meant to be internal link targets within an XCL
>>>> document?
>>>
>>> Not it the first instance, I think.
It's relatively easy to include link targets within an XML document,
either by taking advantage of the inherent ID namespace, or by
designing a custom linking syntax. If you want to be able to define
a formula or statement and reuse it, either within the same document,
or from other documents (as a form of modular design), you'll need
this. If you don't want any linking whatsoever, you've already got
the syntax you need and you won't need me. At least much.
>> We could have them nicely, by using annotations:
>> put a special-syntax string in the annotation and
>> refer to that.
>>
>> But, again, this is ANOTHER LAYER, not SCL spec.
>
> Oh well, OK, but let us allow XML to find its natural layer.
Somewhere between the rice cakes and raw beef.
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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