[SCL] SCL spec

[pat hayes]

>[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.

>>  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.

>[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.

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.)


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