[rules-users] looking for more information on drools expert
Edson Tirelli
tirelli at post.com
Wed Jul 15 10:15:11 EDT 2009
Aldian,
Yes, this is the way to go:
rule "detect and set routers different from root for alarm 45"
When
* All routers which index is different from 0 are raising the alarm 45
* There is an alarm $a of numero 45 raised by an equipement $e
different from the root
Then
* execute some specific code on ($a,$e)
end
It would be like this:
when
forall( $e1 : Equipment( index != 0 )
Alarm( origin == $e1.name, probablecause == 45 ) )
$e2 : Equipment( index != 0 )
$a2 : Alarm( origin == $e.name, probablecause == 45 )
then
// do something with $e2 and $a2
end
The beauty of Rete is that although you are writing constraints like
"index != 0" and "probablecause == 45" twice in the rule, the engine will
optimize and share them, effectively executing them only once for each fact.
Performance will be very good.
Just be careful with what you do in the consequence, because if for
instance you remove $a2, the forall in the rule will immediately become
false, and all subsequent activations will be canceled.
The above is the preferred way of dealing with multiple facts of the same
type, with the rule firing once for each pair ($e2, $a2), but If you want to
gather a set of them all at once, you can use accumulate and collect CEs.
Check the manual.
Regarding the system clock, the problem is that the clock is not a fact
inside the engine, but you are using it to do your reasoning. Meaning it is
changing, but the engine does not know that.
In Drools 5 we implement temporal reasoning and the concept of session
clock. This makes your reasoning process safe, correct and also allows
reproducibility and auditability.
[]s
Edson
2009/7/15 Gab Aldian <aldian.gp at gmail.com>
> 2009/7/10, Edson Tirelli <tirelli at post.com>:
> > Hi Aldian,
> >
> > I think you misunderstood the semantics of forall(). Forall in Drools
> is
> > the same forall quantifier from the First Order Logic.
> >
> > http://en.wikipedia.org/wiki/First-order_logic
> >
> > So, if you want to write a rule that says: "When for all equipments of
> > type 'router' there is an alarm, then raise a general failure alarm".
> >
> > when
> > forall( $e : Equipment( type == "router" )
> > Alarm( source == $e ) )
> > then
> > // raise a general failure alarm
> > end
> >
> > So, if you have 10 routers in the working memory and only 9 of them
> have
> > associated alarms, this rule will NOT fire, because the condition is not
> > matched. But, if an alarm is raised for the 10th router, then all of them
> > have an associated alarm and the rule will fire.
> >
> > So, as you can see, "forall" is a quantifier CE, in the same way that
> > "not" and "exists" are quantifiers. They operate on multiple facts at
> once,
> > and as so, you can not use the variables bound inside their scope outside
> of
> > it. In the above example, if you tried to use $e in the consequence,
> which
> > of the 10 routers would it be bound to? So, since it makes no sense, the
> > engine disallow the usage of variables bound inside quantifiers outside
> of
> > them.
>
> Hello, and Thank you very much for the answer. But your explanation
> shows that my understanding of this keyword was correct. And what if I
> want to ewecute this condition/consequence:
>
> When
> * All routers which index is different from 0 are raising the alarm 45
> then
> * Execute some specific code on all these routers
> end
>
> As you can see If I attribute a $e to the routers from the condition,
> it makes sense hoping to retrieve a reference on these routers to
> execute code on them. I think I will escape this problem doing it with
> two rules:
>
> rule "all routers but the root raise 45"
> When
> * All routers which index is different from 0 are raising the alarm 45
> then
> * write somewhere that rule "all routers but the root raise 45"
> has been validated
> end
>
> rule "set routers about the alarm 45"
> When
> * there is written somewhere that "all routers but the root raise
> 45" has been validated
> * $a : Alarm is raising 45 from an equipement $e different from root
> then
> * execute some specific code on $a and $e
> end
>
> There is also the possibility to do it in only one rule, but I have
> some doubts about time optimization:
>
> rule "detect and set routers different from root for alarm 45"
> When
> * All routers which index is different from 0 are raising the alarm 45
> * There is an alarm $a of numero 45 raised by an equipement $e
> different from the root
> Then
> * execute some specific code on ($a,$e)
> end
>
> this way, drools will proceed to two verifications:
> * if forall routers which index is different from 0, they have raised
> an alarm of numero 45
> * if any alarm $a originated from a routers $e different from the
> root, is of numero 45 and then execute some code on it.
>
>
> >
> > Just to be easier to remember I call quantifier CEs "scope
> delimiters".
> > The general rule is: variables bound inside a scope delimiter are never
> > available outside of them.
> >
> > I don't understand what you are trying to do in your first rule in
> your
> > example. If you write your rule in plain English, the people from the
> list
> > can help you write it correctly.*
>
> I am sorry, English is not my mother language, but I hope you will
> understand a lot. I will know give further explanations on my example:
>
> I am supervising a network of equipements. They are not all routers,
> and actually, they are very different from each others, but you can
> consider them as routers, it doesn't matter. There is a central
> equipement, the root, which centralized all the alarms sent by the
> other equipements. And there is a software that supervise that root
> equipment and that folow me the alarms. I am trying to make
> correlation on some basic cases as this one:
>
> * for all equipements but the root I have the alarm "impossible to
> connect". It is a very common alarm, because we often work with
> virtual equipements, so we know that when we have that alarm on every
> equipement but the root, there is no worry to have. But we would like
> to suppress all that alarms that are all the same to only one that
> agregate all the others. So what we wish to do is the folowing:
>
> when
> * For all equipement different from the root an alarm of type 45
> as been raised,
> then
> * Suppress all these alarms and create an alarm that agregate all
> these alarms in only one
> end
>
> As you can see the ideal would be that the forall allow to attribute
> to a $tabarray variable an Array of type Alarm [] containing all the
> alarms meeting the requirement.
>
>
>
>
>
> >
> > Finally, just for completeness, be careful with the semantics of
> time.
> > Your Alarm class is using the system clock to define timeout, and that
> will
> > give you all kinds of headaches, not to mention wrong/unexpected results.
>
> I suppose you say this because of the risk of unsynchronized clocks on
> the network? But for now I don't see how to improve that...
>
>
> > But this e-mail is already too long. I suggest you take a look at the
> Drools
> > Fusion docs on temporal reasoning.
>
>
> Thank you very much, I will take a look about this
>
> Regards
>
> Aldian
>
>
>
>
>
>
>
> >
> > 2009/7/10 Gab Aldian <aldian.gp at gmail.com>
> >
> >> Hi everybody
> >>
> >> I have read with attention the drools expert documentation, which was
> >> very interesting, but a little 'too simple". For example, most
> >> examples don't present rules with the keyword "forall". I also met big
> >> difficulties mixing the references on the objects to my javacode. This
> >> is why I would need some more documentation with examples that go
> >> deeper into drools capacities.
> >>
> >>
> >> To give you clues about my plan, here is an example (which works
> >> perfectly in drools 5) that I have developed:
> >> java code - http://drools.pastebin.com/m1a705614
> >> rule code - http://drools.pastebin.com/m3f30cbdc
> >>
> >> As you can see I am studying the case where drools is used for the
> >> monitoring of a network of equipments that send alarms about their
> >> problems. But I have big difficulties, because I would like to get
> >> references on the objects of the "forall", and to execute javacode
> >> such as $toto.method($titi, $tata), but such things seems impossible
> >> (systematic failed of compilation)
> >>
> >> Could you please help me?
> >>
> >> Thank you very much!
> >>
> >> Aldian
> >> _______________________________________________
> >> 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 by Red Hat @ www.jboss.com
> >
> _______________________________________________
> 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 by Red Hat @ www.jboss.com
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