[rules-users] Negation semantics in Drools
Edson Tirelli
tirelli at post.com
Fri Apr 17 17:42:36 EDT 2009
Paul,
Yes, you are right.
Now, I am curious. What is the background on this exercise? There are
some problems that are better suited for backward and others better suited
for forward chaining. Most problems would be modeled in very different ways
in each technology.
If we were just searching for the solution, it would just be the case of
writing (in forward chaining) one or two rules that would provide the
correct answer. But since this seems to be an academic exercise, I am
curious to understand the goals of it so that we can properly model it.
Cheers,
Edson
2009/4/17 Paul Fodor <paul.i.fodor at gmail.com>
> 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
> >>>>
> >>>>
> >>>>
> >>>> _______________________________________________
> >>>> rules-users mailing list
> >>>> rules-users at lists.jboss.org
> >>>> https://lists.jboss.org/mailman/listinfo/rules-users
> >>>>
> >>>
> >>>
> >>>
> >>> --
> >>> 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
> >>>
> >>
> >>
> >> _______________________________________________
> >> rules-users mailing list
> >> rules-users at lists.jboss.org
> >> https://lists.jboss.org/mailman/listinfo/rules-users
> >>
> >
> >
> >
> > --
> > 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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