On 19/03/14 16:46, Christophe FAGOT wrote:
Hi Jena folks,
since I need to use Jena with its RETEEngine, I’m actually investigating what
is actually feasible / usable with this engine functionalities.
I would like to develop my own BuiltIn, used in the head of a forward rule, and
doing some actions when a new rule context appears (due to triples adding) for
the body rule, while doing some other actions when a rule context disappears
(dur to triples removal) for this body rule.
It appears in the RETEConflictSet (line 180) that a BuiltIn can receive only …
added RETERuleContext. Hence a BuiltIn action can only be called when a
RETERuleContext is added, never when a RETERuleContext is removed.
Is their a reason for that ?
The existing head builtins expect to only be fired when a potitive
deduction is made. This is a legacy of the fact that the rule system was
designed for monotonic inference and all the remove/non-monotonic
processing is a hack. It was added due to requests on the user's list
but was a mistake.
Note also that since there's no reference counting in the rule system
it's notion of removal is not reliable.
Would it be possible to add in the context whether it’s a context added or
removed, and to call the BuiltIn head action in both cases ?
No because that would change behaviour for existing rules sets,
especially any with custom builtins.
I guess you could have a custom sort of builtin which does support
firing a head-action on a remove and modify RETEConflictSet to check for
such builtins and allow those (and only those) to fire - passing the
isAdd flag as part of the call.
Dave
