[PowerLoom Forum] forward-chaining issue

[Hans Chalupsky]

Dear Pan Xingzhi,

yes, the PowerLoom forward chainer only considers rules with simple
antecedents and rules with complex antecedents that are marked as
`:forward-only? TRUE'.  You can of course get the answer you are
looking for by using backward inference via `ask':

STELLA(163): (all-facts-of com1)
(|P|(COMPANY COM1) |P|(NUMBER-OF-MANAGERS COM1 10) |P|(NUMBER-OF-EMPLOYEES COM1 50))
STELLA(164): (ask (small-company com1))
TRUE
STELLA(165): 

The division of labor between forward and backward chaining is
primarily a performance issue, since depending on fanout, some rules
are much more efficiently run forward than backward and vice versa.
You can help PowerLoom by annotating which rules you want to run
forward and which ones backwards only.

For example, if you want this to be added with the forward-chainer,
you can mark the rule as "forward-only" with the `=>>' notation:

STELLA(165): (assert
               (forall ?c
                 (=>> (and (number-of-employees ?c 50)
                           (number-of-managers ?c 10))
                      (small-company ?c))))
|P|(FORALL (?c)
   (=>> (AND (NUMBER-OF-EMPLOYEES ?c 50) (NUMBER-OF-MANAGERS ?c 10))
       (SMALL-COMPANY ?c)))

STELLA(166): (all-facts-of com1)
(|P|(COMPANY COM1) |P|(NUMBER-OF-MANAGERS COM1 10) |P|(NUMBER-OF-EMPLOYEES COM1 50)
 |P?|(SMALL-COMPANY COM1))
STELLA(167): 

The proposition is only true in an inference-cache world associated
with the current module, which is why it is printed with a question
mark here.  These inference caches are blown away if there are any
retractions or non-monotonic changes, since then they might not be
valid anymore.

Finally, you can use the PowerLoom classifier to eagerly infer all
types of instances and add them to the KB:

STELLA(177): (setq *classify-from-non-inferable-parents-only?* false)
()
STELLA(178): (classify-instances pl-user true)
u
()
STELLA(179): (all-facts-of com1)
(|P|(COMPANY COM1) |P|(NUMBER-OF-MANAGERS COM1 10) |P|(NUMBER-OF-EMPLOYEES COM1 50)
 |P|(SMALL-COMPANY COM1))
STELLA(180): 

Caveat: by default, the variable
`*classify-from-non-inferable-parents-only?*' is set to TRUE which
prevents COM1 to be classified (this is an optimization for
classification of large hierarchies).  Currently, you can't change its
setting with a PowerLoom command which is why I changed it with a Lisp
statement above (or you would have to change the corresponding C++ or
Java variable and then recompile).  In future versions we should make
this available as a user feature that you can change.

Hans

>>>>> Xingzhi Pan <vengeance.storm at gmail.com> writes:

> Hello, friends.
> I've been trying forward-chaining in PowerLoom. It seemed that,
> sometimes PowerLoom will add inferred facts into KB, and sometimes
> not. Try to compare these:

> (defconcept company)
> (defrelation number-of-employees ((?c company)(?n INTEGER)) )
> (defrelation number-of-managers ((?c company)(?n INTEGER)) )
> (defconcept small-company ((?c company)))
> (assert (forall ?c (=> (small-company ?c) (and(number-of-employees ?c
> 50)(number-of-managers ?c 10))) ))
> (assert (small-company com1))
> (all-facts-of com1)

> and

> (defconcept company)
> (defrelation number-of-employees ((?c company)(?n INTEGER)) )
> (defrelation number-of-managers ((?c company)(?n INTEGER)) )
> (defconcept small-company ((?c company)))
> (assert (forall ?c (=> (and(number-of-employees ?c
> 50)(number-of-managers ?c 10))(small-company ?c)) ))
> (assert (company com1))
> (assert (and (number-of-managers com1 10)(number-of-employees com1 50)) )
> (all-facts-of com1)

> I found that PowerLoom will do the inference only when the antecedent
> is an 'atom' proposition. When it's something like (and P Q), nothing
> seems happened. Have I done something wrong? Or it's designed so? Any
> help would be appreciated.
> --
> Pan Xingzhi
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