[SCL] SCL spec

[pat hayes]

>pat hayes wrote:
>>>[small correction to my last message to avoid any confusion.]
>>>
>>>I wrote:
>>>[...]
>>>
>>>>4. Finally, as I've done in my XCL proposal, all components of
>>>>    the language that may be referred to conceptually either in
>>>>    discussions or more particularly by tools should be given a
>>>>    unique identifier. Topic Maps introduced a concept called
>>>>    Published Subject Indicators (PSIs) that are basically just
>>>>    stable URIs used as identifiers. The idea here (which would
>>>>    be useful in Topic Map, RDF, or any other web-related system)
>>>>    is that if two things identify themselves as having the same
>>>>    PSI, they are semantically equivalent.
>>
>>Oh dear, that is a VERY strong statement (and it seems to me rather 
>>naive, to be honest.) Semantically equivalent in what language, 
>>with what model theory? Do you mean they denote the same entity in 
>>all possible models? (Please don't say yes to that question, at 
>>least not quickly: see the uri at w3c.org email archive for some 
>>heated discussions.) This whole matter of there being a global 
>>semantics for URIs seems to me to be woefully under-analyzed at 
>>present, and almost everything written about it is rather naive. 
>>The REST model (and the diluted version assumed in RFC 2396) isn't 
>>up the task without being extended, for sure.
>
>Perhaps I'm being unclear. It's not that machines ever declare two
>things as having identity, but rather people.

People almost never achieve semantic equivalence in normal 
communication. Attempts to approximate it rapidly become unwieldy and 
expensive (eg legal terminology, technical in-house terminology, 
mathematical notations).

>There are no semantics
>whatsoever in URIs, in my opinion.

I disagree, but I think the semantics is subtle and has not yet been 
adequately formalized.

>They're just strings used as
>identifiers (some of which may resolve to something, but that for
>the purposes of this discussion is not important

It is when we have things like imports statements, or ontologies 
which rely on Qname syntax to resolve meanings.

>). This isn't some
>instance of nominalism, this is unambiguous identifiers within
>specific domain namespaces being used to identify concepts.
>
>>>>  For example, if OWL
>>>>    has a concept "http://www.w3.org/2002/07/owl#" and my Ceryle
>>>>    project has a concept "http://purl.org/ceryle/psi/authoring/#Thing",
>>>
>>>[...]
>>>
>>>Cut and pasting I neglected to add "Thing" to the OWL identifier.
>>>This should be "http://www.w3.org/2002/07/owl#Thing" being compared
>>>with "http://purl.org/ceryle/psi/authoring/#Thing". Sorry if this
>>>caused any confusion.
>>>
>>>Without this feature it's difficult (at a tool level) to claim
>>>identity between systems for even things such as "true" or "false".
>>
>>Why would you expect it to even be meaningful to claim identity 
>>between *systems* ? Of course it is difficult to claim identity 
>>across systems which have different underlying semantics: it ought 
>>to be difficult, because it is meaningless.  That is one of the 
>>main purposes of the application of SCL to the Web, to try to 
>>provide a globally coherent semantic framework which can underlie 
>>the various surface notations.
>
>Again, I was unclear. The purpose of PSIs is to identify concepts
>unambiguously.

That seems like an impossible goal. We know that no finite expression 
can completely identify the concepts of arithmetic, such as 'zero'.

>If you and I have two systems, and I'm trying to
>map the interpretation of concepts within your system to the
>interpretation of concepts within mine (e.g., I can determine that
>my "forall" is the same as your "forall" by reading the documentation
>of both systems, therefore their two PSIs identifying the concepts
>can be mapped as equivalent).

But you will almost never find that.  For example, the notion of 
'class' changes when one moves from RDFS to OWL.

>
>>>[perhaps someone can answer me privately on this question: I can't
>>>find "true" or "false" among OWL or RDFS. Is it there and I'm
>>>missing it, or not? Thanks.]
>>
>>Not explicitly. What do you expect those names to mean? There is a 
>>'universally true' class, ie the universe class, which is 
>>rdfs:Resource in RDFS and owl:Thing in OWL; similarly the 
>>'universally false' (empty) class in OWL is owl:Nothing. Different 
>>versions of OWL take different views on the relationship between 
>>rdfs:Resource and owl:Thing, by the way. In OWL-Full they are the 
>>same; in OWL-DL, owl:Thing is a subset of rdfs:Resource, because 
>>the OWL-DL universe doesn't contain classes or properties, for 
>>example.
>>
>>These languages do not have names for what in logic would be called 
>>the truth-values themselves.
>
>Fair enough. I was thinking in terms of truth values, not classes.

There is a natural mapping from truthvalues in logics to classes in a 
description logic.

>In Cyc
>(of which I'm most familiar) it defines #$True as
>
>    An instance of #$TruthValue. #$True is logical truth in Cyc; this is
>    the abstract logical notion--not to be confused with Lisp's T, nor
>    with the English word `true'.

That is not a definition; it is a textual comment.

>
>So if in my Ceryle system I implement an ontology using a root concept
>of "Thing" and I agree with Cyc's #$Thing, shouldn't it be possible to
>consider them equivalent

Almost certainly no. It would be a lot of work to demonstrate that 
they were, for sure. Certainly Cyc's useage in which truth-values are 
themselves items in the universe of discourse is not mirrored in SCL 
(though it could be in a CYC-oriented SCL ontology, I guess)

>, and create a map equivalency between them
>(i.e., I as a human state the relation so that my computer will consider
>them equivalent)?

You as a human can do whatever you like, but it would be a very bad 
(dangerous) idea to write software on that basis.

>
>Would you say that Cyc's set of constants for #$implies, #$not, #$and,
>#$or, #$forAll, #$thereExists, would these have identity (semantically)
>with the SCL list of tokens, "implies", "not", "and", "or", "forall",
>"exists"?

Definitely not.

>If so (and this I would imagine can be determined by reading
>the documentation of each), thenn (is there an equivalent to iff?) we
>can map the PSIs between them:
>
>          http://purl.org/xcl/1.0/#implies
>    maps to
>          http://www.cyc.com/cycdoc/vocab/fundamental-vocab.html#True
>
>          http://purl.org/xcl/1.0/#exists
>    maps to
>          http://www.cyc.com/cycdoc/vocab/fundamental-vocab.html#thereExists
>
>   et cetera.

Well, yes, but we can do this with any other URIs or indeed any other 
identifiers at all.  What functionality does the PSI provide in 
particular?

>assuming the publishers of Cyc decided to use their HTML URLs
>as PSIs. This would simply be a matter of them declaring that to
>be the case, and to conform to the PSI recommendations/best
>practices, to publish some metadata about the set. You can see
>this at:
>
>   http://purl.org/xcl/1.0/#psimeta
>
>Now, I'm perhaps (okay, likely) naive, but I'm not sure what else
>one can do to state the equivalence between two concepts.

I would presume that the relationship between them would be stated in 
an SCL ontology of some kind. The simplest 'mapping' would just a 
bunch of equations, though that is unlikely to be adequate in this 
case.

>
>[Actually, since the Cyc publishers might be listening, I'd certainly
>advocate "publishing" the PSI set for Cyc. Last time I talked with
>Doug he said that the individual URLs for each Cyc constant could be
>considered stable. One could publish them under their current URLs,
>or add each constant name to some base URL. The former would be
>preferred, IMO, as the OASIS technical committee handling PSIs has
>recommended that PSIs resolve to human-readable documentation (if
>I remember correctly). You could create a PURL domain for Cyc do
>this redirecting in that manner so that the Cyc PSIs would be
>independent of the web site domain, perhaps a strategy for gradual
>transition over to opencyc. So these two would be equivalent, the
>first redirecting to the second:]
>
>    http://purl.org/cyc/fundamental-vocab.html#True
>    http://www.cyc.com/cycdoc/vocab/fundamental-vocab.html#True
>
>[At some point, you'd just change the redirect from cyc.com to
>opencyc.org... any questions on this just ask.]
>
>>Pat
>>
>>PS. You might find the translation of OWL into Lbase (a version of 
>>SCL) helpful in keeping track of things 
>>http://lists.w3.org/Archives/Public/www-archive/2003Mar/att-0018/LBASE-new.html
>>(This is slightly out of date now on the XML literal details, so 
>>ignore that stuff at the beginning; and its incomplete as OWL has 
>>grown since it was written, but it will give you the idea.)
>
>Thanks -- will do. I must admit my first reading of LBase didn't
>stick in my head, but I think I understand a few of these things
>a bit better now.
>
>Ahh, just occurred to me. I see in Cyc both #$tuple and #$Relation.
>During the telecon we talked about n-tuples, whereas I'd been thinking
>syntax-wise more along the lines of #$Relation.
>
>Now, a question came up (I think from John) about whether Topic
>Maps are/will be important technology. I believe so, but that's
>just my opinion. What I think is more important is that for the
>CL specs we include PSIs,

PSIs are a new idea for me. I am not particularly impressed so far 
and I don't see any wide use in other communities. But what the hell, 
there is no harm, I guess, in having a set of them. However it is 
important for SCL that we do not mandate the use of PSIs (or indeed 
any other particular syntactic conventions)

>so that *whatever* technology is used
>in implementing CL-based systems, there's a way to unambiguously
>label each language component (what did John call these? grammar
>things? can't remember now. I'd been calling them syntax
>"productions"). So if RDF or TM fails or succeeds, if URLs are
>still being used as identifiers in ten years, CL concepts will
>still be identifiable.
>
>Enough for now. Chris, when you edit your next version of the spec,
>could you be so kind as to perhaps add in square bracketed tokens
>for each part of the abstract syntax you think should be identified
>as a "grammar thing"? (gad, my memory today is shot). If you look
>at the XML Recommendation
>
>   http://www.w3.org/TR/REC-xml
>
>you can see what I mean by production numbers ([1], [2], etc.).
>
>Murray
>
>......................................................................
>Murray Altheim                    http://kmi.open.ac.uk/people/murray/
>Knowledge Media Institute
>The Open University, Milton Keynes, Bucks, MK7 6AA, UK               .
>
>   [...T]here will be a simulated biological attack on Chicago, with
>   thousands of patients showing symptoms of serious illnesses
>   beginning to appear in the city's hospitals on Tuesday. [...] The
>   exercise is planned to end on a positive note, with suspects being
>   arrested at the end of the week.
>             -- "US drills for terror attacks", BBC News, 12 May 2003
>
>   The terrorist attack is taken for granted, but endlessly postponed.
>   The true catastrophe is that we are living under a permenent threat
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>
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