[rules-users] Negation semantics in Drools
Paul Fodor
paul.i.fodor at gmail.com
Fri Apr 17 17:13:43 EDT 2009
Hi Edson,
The "insertLogical" doesn't work for non-stratified programs.
For instance, in the win-nowin example, if there is a move(1,2) and
a move(2,1), the order in which the two facts are inserted determines the
final model (please see hte tests below).
In logic programming, this example has two stable models: {win(1)} and
{win(2)}, or a well-founded model {} (win(1) and win(2) are both undefined).
Regards,
Paul.
*
package
* tests;
*
import
* tests.Test.Win;*
import
* tests.Test.Move;
*
rule
* "direct"
*when*
m : Move(x : first, y : second)
*not* Win(first == y)
*then*
*insertLogical*(*new* Win(m.getFirst()));*
end
*
move
1
2
move
2
1
Test:
reading rulefile: win.drl ...
reading datafile: win_upper3_drools.drools ...
loading cputime: 0.016
loading walltime: 0.016
calculating ...
computing cputime: 0.0
computing walltime: 0.0040
Derived facts in memory:move(1, 2).
win(2).
move(2, 1).
3
move
2
1
move
1
2
Test:
reading rulefile: win.drl ...
reading datafile: win_upper4_drools.drools ...
loading cputime: 0.016
loading walltime: 0.016
calculating ...
computing cputime: 0.0
computing walltime: 0.0040
Derived facts in memory:move(2, 1).
win(1).
move(1, 2).
3
2009/4/17 Edson Tirelli <tirelli at post.com>
>
>
> 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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>>>>
>>>
>>>
>>>
>>> --
>>> 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
>
> _______________________________________________
> rules-users mailing list
> rules-users at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>
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