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Dan Connolly | 17 Feb 2011 06:31

equality reasoning with functions and existentials?

I discovered powerloom the other day via a tweet
  http://twitter.com/danja/status/37660228791042048

It looks pretty nifty.

I'm trying to tell it:

 state-code is unambiguous (i.e. its inverse is a function).
 There's a place with state-code "KS" and population 28000.
 There's also a place with state-code "KS" and state-bird western-meadowlark.

and then ask it:
 Is there a place with population 28000 and state-bird western-meadowlark?

The attached is my attempt. It's *almost* working, but not quite. I
don't understand why not.

Clues, please, anyone?

--
Dan Connolly
http://www.madmode.com/
Attachment (,same-state.plm): application/octet-stream, 1507 bytes
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Hans Chalupsky | 17 Feb 2011 21:26
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Re: equality reasoning with functions and existentials?

The problem is that PowerLoom's just-in-time forward inference isn't complete
enough here to pick up all that's required, and you have to run forward rules
explicitly.  When you define an "inverse" for a relation, the required rules
are created by forward inference which isn't triggered by the JIT in this
case.  As an aside, inverse relations in a logic system like PowerLoom are
redundant and generally a bad idea for performance reasons.  Also, if you
declare an inverse on one relation, you shouldn't also do it on the inverse,
since it will generate redundant rules.  I know, PowerLoom should adivse users
on that, but currently it doesn't :-)

Anyway, after you do a "run-forward-rules" in the trace below, you get the
answer you are looking for.

Hans

STELLA(99): (clear-module pl-user)
:VOID
STELLA(100): (deffunction the (?i) :-> (?x Thing))
|f|THE
STELLA(101): (defrelation state-code (?s ?c)
  :axioms (inverse code-state state-code))
|r|STATE-CODE
STELLA(102): (deffunction code-state (?c ?p)
  :axioms (inverse state-code code-state))   ;; this is redundant and should be avoided
|f|CODE-STATE
STELLA(103): (defrelation state-bird (?place ?birdtype))
|r|STATE-BIRD
STELLA(104): (defrelation population (?place ?pop))
|r|POPULATION
STELLA(105): (assert (exists (?x) (and (state-code (the ?x) "KS")
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