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CORE: nascent issues list

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Fri, 15 Aug 2008 16:07:45 +0100
Message-ID: <48A59BC1.8020502@hplb.hpl.hp.com>
To: RIF WG <public-rif-wg@w3.org>

We have discussed the starting points for Core as:
   - roughly the datalog subset of BLD, plus Frame syntax and externs
   - the intersection of PRD and BLD
   - something as simple to implement as possible while still being useful

I thought it might be useful to try to enumerate the questions that 
would need to be resolved to ground this out. I'm not proposing all of 
these as formal issues yet, nor describing them in adequate detail, just 
trying to collect an initial list to get a sense of where the problems are.

1. Decidability?

Should there be a rule safety criteria? Should it be normative?

2. Handling of external functions?

DTB defines many operations that would be useful in CORE but defines 
them as functions rather than predicates.
Options here would include:
(a) allow some syntactically restricted assignment-like use of equality 
in CORE to allow the results of external functions to be accessed;
(b) define predicate versions of those functions as part of CORE.
(c) define predicate versions of those functions in DTB.

3. Support for skolem functions or some equivalent?

C.f. Gary's thread. In applications terms it's useful to be able to 
create new objects (to use PR terminology). In BLD this can be achieved 
by use of function symbols. Some equivalent is a requirement on PRD. How 
does this impact CORE?

Options here might include:
(a) not in CORE
(b) restricted use of function symbols just for this purpose, if the 
restrictions can be well defined
(c) some genSym builtin

4. Membership/subclass?

We've previously suggested these be omitted form CORE on the grounds 
that CORE is minimal and those were contentious.

For PR systems based on an object model there seems to be some argument 
these are needed and are thus in the intersection of PRD and BLD. So 
should they be in CORE?

5. Frames only?

Not sure this is a serious option but thought I'd raise it.

As far as I can tell many PR systems only support an object data model 
and so would natively only support Frames, not uniterms. The same is 
also true of RDF rule languages like N3 and Jena.

It would in principle be possible to have a CORE with just Frame syntax 
plus external predicates but no non-external uniterms which would reduce 
the implementation barrier for such systems.



What other issues have I missed?

Dave
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Received on Friday, 15 August 2008 15:09:11 GMT

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