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Re: question about frames

From: Gary Hallmark <gary.hallmark@oracle.com>
Date: Thu, 08 May 2008 23:43:50 -0700
Message-ID: <4823F2A6.7060903@oracle.com>
To: RIF WG <public-rif-wg@w3.org>

Michael and Jos,

Thanks for clear answers to a not-so-clear question.  Let me expand just 
a bit.  In my PR system (OBR), the action that corresponds most
closely to a rule "head" or conclusion is the so-called "assert new" 
action.  This action creates a new java object (a frame instance of a 
given class) , initializes its javabean properties (slots) with given 
values, and asserts it to Jess.

I want to translate some subset of my rules to BLD, namely rules without 
negation, aggregation, or actions other than assert new.

Here is a simple rule (fusing OBR and BLD syntax):

IF and(?p#P ?p[x->?x]) THEN assert new Q[x->?x]

Do I translate to this:

forall ?x ?p (Q(?x) :- and(?p#P ?p[x->?x]))

That seems a little wrong.  OBR doesn't support relations, only frames, 
but it lets one use frames instead of relations. But BLD doesn't really 
let one dispense with relations and use only frames.  Is this also an 
issue for RDF + RIF?

Possibly this translation, that seems more faithful to the original, is 
closer to legal BLD:

forall ?x ?p ?q (and(?q#Q ?q[x->?x]) :- and(?p#P ?p[x->?x] 

here, new() is a builtin that returns a new instance of a frame.  Is 
"new", not being a mathematical function, no-good for BLD semantics?
it seems to interfere with removing the conjunct from the head.

kifer@cs.sunysb.edu wrote:
>> I'm wondering how to write some simple rules using frames because frames 
>> map to the Java beans that Oracle Business Rules uses as its facts 
>> better than relations.  Or so I hoped.  The problem I seem to be having 
>> is with frame OIDs.  I don't want to have to specify them in a rule 
>> conclusion.  For example, consider the simple rule using relations p and q:
>> forall(?x) Q(?x) :- P(?x)
>> How do I do this using frames instead of relations?  I think I want
>> forall(?x, ?p) and(exists(?q) ?q#Q[x->?x]) :- ?p#P[x->?x]
>> Unfortunately this is illegal in BLD because heads cannot be formulas, 
>> only atomic.  How can I conclude (assert) that frame a instance exists 
>> without giving its OID?  Or do we need some kind of gensym builtin for 
>> this?
> What you want to do is not possible *in principle* in a Horn-based language
> like BLD. The best you can do is to approximate this with a function symbol:
> forall ?x ?p and(f(?p)#Q  f(?p)[x->?x]) :- and(?p#P ?p[x->?x])
> or (depends on what you are up to)
> forall ?x ?p and(f(?x ?p)#Q  f(?p)[x->?x]) :- and(?p#P ?p[x->?x])
> What you want to do is possible in FLD, however. (More precisely, in an
> FLD-based extension of BLD.)
> 	--michael  
Received on Friday, 9 May 2008 06:45:07 UTC

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