[rules-users] Mechanism to prevent redundant inferences

[Tracey Lall]

Hi folks

  I am writing a logical inference engine in drools. Logical sentences (class
Sentence) which are proven are indicated by the fact Proven( sentence =
$sentence )

All Proven(sentence) facts are asserted using the drools logical mechanism
(since logical backtracking is required).

For efficiency purposes I want to be able to suppress firing any rules which
 assert proof of a logical sentence which has already been proven (there may
be multiple inferences which prove the same sentence).

If the non existence of a proof of a sentence (not exists
Proven(sentence=$sentence) is included in the lhs conditions then that
causes problems when the rule logically asserts Proven(sentence) since the
insertion invalidates the lhs conditions and hence the rule causes its own
retraction (the inserted fact handle return is null).

As a way around this I created a class Piton() to record whether a
particular rule has fired. The lhs conditions then become:

(Proven( predicate == $sentence ) or Piton( fireName == $descriptor ) )
And then in the body of the rule the first thing it asserts is the fact:

Piton( fireName == $descriptor )

Where $descriptor is a string built from the rulename  + the set of facts
which matched the lhs (ie a descriptor which is unique to the rule fire)

With this approach when a rule asserts Proven(sentence) because it has also
asserted  Piton( fireName == descriptor ) ) the lhs of the rule still
matches the the rule fire is not retracted.

This approach works, but it is rather tedious to implement since the
descriptor must be defined in such as way to make it unique (or as far as
possible unique) to the particular rule activation. Since the drools
variable is not accessible in the lhs of a rule (and hence the activation
details are not accessible in the lhs), this means that the descriptor must
be handcoded to consist of all matching facts for that lhs.

Is this approach the only way to prevent multiple rule firings for the same
proof, or is there a simpler way to achieve this?

Any advice greatly appreciated!

thanks

Tracey
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