Regarding this particular question from my initial message:
> Any thoughts from anyone about what would be involved in modifying
the Jena code base to support this?
It looks like what I'm asking for would be reasonably easy. It looks
like the high-level steps would be:
* Modify the rule representation to store a numeric priority
* Define a rule syntax modification for how to state a numeric priority
* Modify the rule parser to parse out the numeric priority and put it
into the rule representation
* In RETEConflictSet, write a new method to choose a rule to fire
based on these priorities. The place to call that method (hopefully
the only place needed) would be in RETEConflictSet.fireOne.
So I guess I'll add the following question: Does that sound right to
those to know the code well?
Cheers,
David
On 10/5/2016 6:15 PM, David Martin wrote:
Hi Niels,
Thanks for the excellent observations/suggestions. Yes, I think you
are right that we could adopt these techniques that leverage what's
provided in the basic RETE algorithm, which are already implemented in
Jena. However, we strongly prefer a more streamlined approach. For
one thing, the "bookkeeping" clauses and assertions in the rules can
get to be really cumbersome and can seriously impact the readability
of the rules, and can be hard for the rules author to wrap his head
around once you get beyond a few rules. Rules ease-of-authoring is a
big requirement for us.
So we've concluded that we want an approach that's very easy for the
rules writer to read and think about, and more tightly integrated with
rule-firing choices that happen under the hood.
We've thought a little bit about using the techniques you've mentioned
to support a preprocessing approach. That is, the rules author would
simply write the numeric priorities, but some kind of preprocessor
would generate the bookkeeping clauses and assertions just before (or
just after) the rules are loaded. That might work out pretty well,
but I'd still like to find out if the Jena gurus think this could be
done in a more elegant fashion by modifying the existing Java
rule-firing code. (And if anyone has already worked on this.)
Best regards,
David
On 10/5/2016 3:57 PM, Niels Andersen wrote:
David,
Could you put the priority into the rule and then let the rule
completion trigger the next set of rules?
Another option is to create the rule so that each rule tests to see
if there are any overlapping rules that have a higher priority.
Niels
-----Original Message-----
From: David Martin [mailto:[email protected]]
Sent: Wednesday, October 5, 2016 15:28
To: [email protected]
Subject: Adding priorities to Jena rules?
Hi all,
We are working on a system that employs Jena rules, and we're finding
it would be extremely valuable to have a capability for specifying
rule priorities. We are using the forwardRETE reasoning mode.
What we're thinking of would be the ability of the rules author to
assign a numeric priority to each rule. When the system chooses a
rule to fire, if there are multiple possibilities, one of the rules
with the highest numeric priority is chosen.
Priorities have been added in various ways to many different rules
reasoning systems. Indeed, Wikipedia's article on RETE mentions rule
priorities as one of the typical considerations used in conflict
resolution.
My questions:
Is there anything like this already in Jena, which I am not yet aware
of?
Has anyone ever designed or implemented an approach to support
priorities in Jena rules?
Is this something that might be on the roadmap for future evolution
of Jena rules?
Any thoughts from anyone about what would be involved in modifying
the Jena code base to support this?
Finally, in the current implementation, is the ordering of rules
(order in which the rules have been loaded) decisive in conflict
resolution?
Thanks!
David
