[SCL] SCL OMD metamodel

[pat hayes]

Folks, just for info: A small group of people (Elisa Kendall, David 
Frankel, Deb McGuinness) have been drafting some ODM descriptions of 
logics in connection with a Darpa project headed by Deb. They bring a 
new perspective to all of this stuff. So far they have done KIF and 
are busy doing SCL, with me tagging along. They expect to have it 
finished by next week some time, at which point we can put it on the 
SCL website for all to peruse and where it will be a very useful 
resource for us. ODM is the flagship standard for this kind of 
abstract syntax description. This is why I needed to get the core 
syntax locked down ASAP, btw.

(I tried to distribute this thing by email, but the attachment was 
too much for the SCL webserver. I'll put it up on a website when it 
is done.)

In the meantime, the first session produced some suggestions. First 
was that having equational atoms singled out as a special case is not 
really useful and complicated the syntax class hierarchy needlessly: 
and that in any case, there is considerable expressive utility in 
allowing a variadic equality. I have therefore taken the liberty of 
removing equations as a syntactically distinct sentence form, and 
instead classifying '=' as a special name, i.e. one to which a fixed 
semantics is attached. There are other such names in SCL in any case, 
so we have a precedent.

Now we can write things like

(= = owl:sameAs)

by the way :-)

Also, working through this process identified a bug in the EBNF 
grammar which I have now fixed by making a syntactic distinction 
between 'reserved' strings (and, not, or, forall, etc.) which define 
the SCL syntax and therefore cannot be used as names under any 
circumstances, and 'special names' which are just names in the syntax 
but which have special *semantic* conditions attached.

The main document at http://www.ihmc.us/users/phayes/SCL_december_3.html
now has these changes in the syntax.

Pat
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