[rules-users] Negation semantics in Drools
Edson Tirelli
tirelli at post.com
Fri Apr 17 12:45:42 EDT 2009
I did not had time to analyze what jess is doing, but note that what is
important is the final answer. In your example, with Move(1,2) and
Move(2,3), the final answer must be Win(2), right? And that is what Drools
will answer, does not matter the order in which the data is entered into the
engine.
BUT, *very important*: the following construct in backward chaining:
win(X):- move(X,Y), not(win(Y)).
Is better represented in forward chaining using *logicalInsert* instead
of a regular *insert*:
rule "direct" % Drools
when
m : Move(x : first, y : second)
not Win(first == y)
then
logicalInsert(new Win(m.getFirst()));
end
Since in your backward chaining rule, only one win() predicate
instantiation will remain true.
So, even with differences in the reasoning algorithm, the answer is
correct.
Please explain further if I am missing anything.
Edson
2009/4/17 Paul Fodor <paul.i.fodor at gmail.com>
> Hi Edson, Greg,
> I don't think the rule is written wrong. This is how the win-nowin program
> is written in logic programming: X wins if there is a move from X to some Y
> and Y doesn't win:
> win(X):- move(X,Y), not(win(Y)).
>
> rule "direct" % Drools
>
> when
> m : Move(x : first, y : second)
> not Win(first == y)
> then
> insert(new Win(m.getFirst()));
> end
>
> I think that it's interesting that, in Jess (another production rule
> system), the stratified model is always computed right, no matter what was
> the order of the facts in the database. If you want to take a look, please
> see the equivalent program in Jess for win-nowin that I attached. Just run
> it with:
> jess test.clp
>
> win_upper1_jess.jess
>
> (move (cur 1) (next 2))
> (move (cur 1) (next 3))
> (move (cur 2) (next 4))
> (move (cur 2) (next 5))
> ...
>
> win_upper2_jess.jess
>
> (move (cur 2) (next 4))
> (move (cur 2) (next 5))
> (move (cur 1) (next 2))
> (move (cur 1) (next 3))
> ...
>
> test.clp:
>
> (deftemplate move (slot cur) (slot next))
> (deftemplate win (slot val))
>
> (defrule find_win
> (move (cur ?cur) (next ?next))
> (not (win (val ?next)))
> =>
> (assert (win (val ?cur)))
> )
>
> (defquery query-win
> (win (val ?val))
> )
> (open "win_result.txt" output a)
> (printout output ./win_upper1_jess.jess crlf)
> (reset)
> (load-facts "./win_upper1_jess.jess")
> (bind ?tmx (call java.lang.management.ManagementFactory getThreadMXBean))
> (deffunction cputime () (return (* (?tmx getCurrentThreadCpuTime) 1E-9)))
> (bind ?starttime_wall (time))
> (bind ?starttime_cpu (cputime))
> (run)
> (bind ?query_result (run-query* query-win))
> (bind ?count 0)
> (while (?query_result next)
> (++ ?count)
> )
> (printout output "solutions: " ?count crlf)
> (bind ?endtime_cpu (cputime))
> (bind ?endtime_wall (time))
> (bind ?walltime (- ?endtime_wall ?starttime_wall))
> (bind ?cputime (- ?endtime_cpu ?starttime_cpu))
> (printout output "computing cputime: " ?cputime crlf)
> (printout output "computing walltime: " ?walltime crlf)
> (close output)
>
> Regards,
> Paul Fodor.
> 2009/4/16 Edson Tirelli <tirelli at post.com>
>
>
>> Ha, thanks a lot Greg. I need new glasses... he is actually comparing
>> with the parameter "second", but when creating the win fact, using the
>> parameter "first".
>>
>> not Win(first == m.second)
>> insert(new Win(m.first));
>>
>> Yes, in this case the engine is working exactly as it should.
>>
>> Anyway, I added the (fixed) test case to the codebase, just in case. :)
>>
>> Thanks,
>> Edson
>>
>> 2009/4/16 Greg Barton <greg_barton at yahoo.com>
>>
>> You don't have to worry. The engine is acting as it should.
>>>
>>> The rule Paul had was this, a bit simplified for clarity:
>>>
>>> rule "direct"
>>> when
>>> m : Move()
>>> not Win(first == m.second)
>>> then
>>> insert(new Win(m.first));
>>> end
>>>
>>> If the insertion order is [Move(1,2), Move(2,3)] then the rule matches
>>> first on Move(2,3) and Win(2) is inserted. No other rule fires because now
>>> Move(1,2) and Win(2) match up, removing the instantiation with Move(1,2)
>>> from the agenda.
>>>
>>> If the insertion order is [Move(2,3), Move(1,2)] then the order is this:
>>>
>>> matched Move(1,2) insert Win(1)
>>> matched Move(2,3) insert Win(2)
>>>
>>> The insertion of Win(1) in the first firing does NOT prevent the
>>> instantiation with Move(2,3) from then firing.
>>>
>>> So it's all good. :) Sample code and output attached.
>>>
>>> --- On Thu, 4/16/09, Greg Barton <greg_barton at yahoo.com> wrote:
>>>
>>> > From: Greg Barton <greg_barton at yahoo.com>
>>> > Subject: Re: [rules-users] Negation semantics in Drools
>>> > To: "Rules Users List" <rules-users at lists.jboss.org>
>>> > Date: Thursday, April 16, 2009, 8:50 PM
>>> > It is on the latest snapshot release,
>>> > 5.0.0.20090417.005612-483
>>> >
>>> > --- On Thu, 4/16/09, Edson Tirelli <tirelli at post.com>
>>> > wrote:
>>> >
>>> > > We need to investigate if that is still happening
>>> > in
>>> > > latest trunk.
>>> >
>>> >
>>> >
>>> > _______________________________________________
>>> > rules-users mailing list
>>> > rules-users at lists.jboss.org
>>> > https://lists.jboss.org/mailman/listinfo/rules-users
>>>
>>>
>>>
>>>
>>> _______________________________________________
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>>> rules-users at lists.jboss.org
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>>>
>>>
>>
>>
>> --
>> Edson Tirelli
>> JBoss Drools Core Development
>> JBoss, a division of Red Hat @ www.jboss.com
>>
>> _______________________________________________
>> rules-users mailing list
>> rules-users at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/rules-users
>>
>>
>
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>
--
Edson Tirelli
JBoss Drools Core Development
JBoss, a division of Red Hat @ www.jboss.com
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