[rules-dev] Determining if a class is an event or not
Felipe Piccolini
felipe.piccolini at bluesoft.cl
Mon Nov 12 14:04:05 EST 2007
Edson,
As I see it,
Solutions (1) and (2) lend the responsabilitie of knowing what
they are doing on developers, and can be tricky...but at the end
could be
an optimal solution...so they should exists.. solution (3) makes all
the work clean and easy, but can introduce over load work, so for first
instance I'll set up solution (3) so an advanced developer coul
deactivated by developer with some config API, so they could make their
application work faster if they know what they are doing...
OF course i dont like to break the POJO paradigm on drools, is one of
the things make drools THE choice... but introduce extra check to
add a feature that maybe not all devs will use is something that an
advanced dev should decide...
my 2 cents..
:)
btw: Im a little lost on this event feature (last moths Iv been
working on other things) so, where can I read about this event
handle?..is a new
feature from 4.0.2?...is on the docs? Thx.
On 12-11-2007, at 13:54, Edson Tirelli wrote:
>
> Mike, Felipe and Matthias,
>
> Thank you for all your feedback. It really helps to understand
> the different point of views.
> I will try to summarize my understanding of the issue based on
> your comments so far and on the technical requirements of the
> system. First we need to understand the 2 different times where the
> information about an instance of a class (fact) being an event or
> not is needed:
>
> * At compile time: this is required to actually create the
> optimized network (including the ObjectTypeNodes that Mike
> mentions). It is a must have and we can't avoid it. The best way to
> do that IMO is using a specific declarative statement in the rules
> files. I'm thinking about either an "import event x.y.z.Event"
> statement, or a specific "declare event x.y.z.Event". This is pure
> syntax to let the engine know what is an event and what is not, at
> rulebase compilation time. If most users think a syntax like "I
> want to declare that the x.y.z.Event instances are events" is more
> appropriate, :) we could do it, but as it is today, I like the idea
> of using a simple "event" keyword in import statements, the same
> way we import static functions:
>
> import a.b.c.Fact; // a simple fact import
> import function java.lang.Math.max; // a static function import
>
> import event x.y.z.Event; // an event import
>
> If we were an engine working with templates or any other type
> of fact that did not allows inheritance, that would completely
> solve the problem. But we work with POJOs as facts, and POJOs
> (being plain java) support inheritance. So:
>
> * At runtime: even knowing, at compile time, that x.y.z.Event is an
> event, at runtime a user may assert p.q.r.AnotherClass into working
> memory. Now, is p.q.r.AnotherClass an event or not? We need to
> determine that at the time the first instance of p.q.r.AnotherClass
> is asserted into the working memory. At this time, in runtime, we
> create an ObjectTypeNode for this fact class that previously was
> not known by the engine. A few options on how to determine that
> were discussed here:
>
> 1. Mandate all classes that are events implement an "Event"
> interface. I don't like this solution, as mentioned in a previous e-
> mail, because it breaks the Drools paradigm of working with user
> defined domain models, without contaminating them with drools
> specific code. Although, by your comments, seems that this would be
> an acceptable solution.
>
> 2. Create a separate API (something like "session.insertEvent()")
> to insert events into the working memory. This would also "solve"
> the problem, but:
> * "What happens if a user uses this API to insert a class that was
> not declared as event at compile time?". From a technical
> perspective, this will lead to unpredictable behavior and possibly
> to inconsistencies in the reasoning algorithm, specially because
> events do not need shadow facts (they are supposed to be immutable).
> * "What happens if a user uses the regular 'session.insert()' API
> for a class that was declared as an event at compile time?". Same
> as above with the additional problem that the user may try to call
> update() or retract() for that given fact, what is not allowed for
> events. Again, unpredictable behavior.
> My worry is that the only solution for the above 2 issues would
> be to implement a verification routine that would validate if a
> fact asserted as event is indeed an event according to what was
> declared at compile time, and vice-versa. Note though, that this
> validation procedure would be basically the same required for
> solution number 3 bellow, but would have to be executed at every
> insert()/insertEvent() call, making it more costly than the
> completely automated decision.
>
> 3. Implementing an automated decision procedure, analyzing the
> class hierarchy of the inserted fact, every time a fact of a
> previously unknown class is inserted into working memory. Due to
> the problems presented in the previous solutions, this is still my
> preferred approach. Its main drawback is the class hierarchy
> analysis that is not simple to do and at the same time is a bit
> heavy, but would happen only when the first fact of a previously
> unknown class is inserted into working memory.
>
> So, we can probably implement solution (1) and (2) as options,
> but at this time, I can't see how to avoid implementing support for
> (3). But having (3), is it worth to have (1) and/or (2) too, or
> would it only confuse users?
>
> Thanks all for all the feedback so far.
>
> []s
> Edson
>
> 2007/11/12, Anstis, Michael (M.) <manstis1 at ford.com>:
> Hi Felipe,
>
> I recall Edson saying that "Event" classes need to be ascertained
> at (RETE) compilation time - which, I think, rules out the API
> addition. I was hoping Edson, time permitting, would explain how
> declarative (fact-centric class) imports currently work to generate
> an ObjectTypeNode and therefore to understand how his proposal to
> create cached ObjectTypeConf instances for Event-centric classes
> compares. My reasoning being that if the process is similar the new
> event stuff should be no different; simply having two
> ObjectTypeNodes - one for Events and another for Facts. See attached.
>
> It's quite possible our exchanges have given Edson time to come to
> his own conclusion and the solution is now being coded!
>
> With kind regards,
>
> Mike
>
> From: rules-dev-bounces at lists.jboss.org [mailto:rules-dev-
> bounces at lists.jboss.org] On Behalf Of Felipe Piccolini
> Sent: 12 November 2007 13:25
> To: Rules Dev List
>
> Subject: Re: [rules-dev] Determining if a class is an event or not
>
> Well,
>
> IMHO for the experience I have I suggest to implement both
> solutions:
> -an API insertEvet() so the user can implement the mechanism to manage
> their rules knowing when a fact is an event or not.
> -an Interface Event so when the user cant manage the flow asserting
> facts, when
> he cant know when a fact is or not an event, then maybe he can wrap
> some facts on this
> interface and the API insert() internaly can check if the fact is
> an event or not and call insertEvent if
> necesary.
>
> :)
>
> On 08-11-2007, at 11:27, Anstis, Michael ((M.)) wrote:
>
>> Here's my 2 cents - as a non-contributor to Drools codebase ;-)
>>
>> You could add insertEventFactTypeThingie to the API? Then you need
>> just
>> check that the class has been declared as an event in the DRL
>> similar to
>> what must already happen for normal DRL imports. I personally
>> don't have
>> issue with implementing a marker interface (this is what
>> frameworks like
>> Hibernate, EJB3 and Spring etc have been imposing for years). What
>> "wiring"
>> does the POJO need to become an Event for use in Drools? Are you
>> trying to
>> internalise too much at the risk of making the event mechanism
>> inflexible?
>>
>> Cheers,
>>
>> Mike
>>
>> -----Original Message-----
>> From: rules-dev-bounces at lists.jboss.org
>> [mailto:rules-dev-bounces at lists.jboss.org] On Behalf Of Matthias
>> Sent: 08 November 2007 13:09
>> To: rules-dev at lists.jboss.org
>> Subject: Re: [rules-dev] Determining if a class is an event or not
>>
>> Edson Tirelli <tirelli <at> post.com> writes:
>>
>>>
>>>
>>> All, I reached a point where I need to make a design
>>> decision and
>> would
>> like your opinion about it. Imagine the following scenario: A
>> user has a
>> domain model like this:package a.b.c
>>> ;public interface Event { ... }package x.y.z;public class MyEvent
>> implements
>> a.b.c.Event {...} Then, in his DRL file he writes:package
>> p.q.r;import
>> event
>> a.b.c.*; rule Xwhen
>>> Event( ... )then ...end So, it is clear that a.b.c.Event
>>> should
>> be
>> handled as an event by the engine. At runtime, the user asserts
>> an object
>> of
>> the class x.y.z.MyEvent into the working memory. Seems clear to me
>> (and
>> probably
>> to the user) that MyEvent should be handled as an event, since by DRL
>> semantics,
>>> a.b.c.* are all events, and by OO class hierarchy concept, since
>> a.b.c.Event
>> is an event, x.y.z.MyEvent is an event too. My question is: how
>> the engine
>> knows that MyEvent is an event, since it only has the x.y.z.MyEvent
>>> class as input? The only answer I have is that when the first
>>> MyEvent
>> instance is asserted into the working memory, we must get the
>> class name and
>> iterate over all event import declarations checking for a match.
>> In case no
>> one
>> is found, we need to repeat the process for each interface and
>> each class up
>> in
>> the MyEvent hierarchy. Once this process is complete, we cache the
>> results
>> in
>> the ObjectTypeConf.
>>> This may be a quite heavy process to be executed each time a
>>> fact of a
>> different class is asserted in the working memory for the first
>> time, but I
>> can't think a different user-friendly way to solve the question.
>>> The alternatives would be intrusive, IMO, breaking the drools
>>> premise
>> to
>> work with user-defined POJOs as facts: use anotations to annotate
>> classes
>> that
>> are events, or mandate users implement a specific interface for
>> events.
>>> Any better idea? []s Edson -- Edson Tirelli Software
>> Engineer
>> - JBoss Rules Core Developer Office: +55 11 3529-6000 Mobile:
>> +55 11
>> 9287-5646
>>> JBoss, a division of Red Hat <at> www.jboss.com
>>>
>>>
>>> _______________________________________________
>>> rules-dev mailing list
>>> rules-dev <at> lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/rules-dev
>>>
>>
>>
>> Edson,
>>
>> I got your striving not to mandate users implement a specific
>> interface for
>> events. However, why not at least introducing an empty event
>> interface (i.e.
>> a
>> marker interface, similar to the Serializable interface in Java) the
>> user-defined event class(es) have to implement? This way, when
>> inserting a
>> MyEvent instance, you can simply check whether it implements the
>> event
>> interface
>> (by means of 'instanceof'). Moreover, while parsing the import
>> statements of
>> a
>> rule file, it enables you to double-check whether all the "event
>> imports"
>> really
>> refer to classes implementing the (empty) event interface.
>> In this regard, for me another question raises: Without making any
>> restrictions
>> on the structure for a user defined event class, how do you make
>> sure it has
>> all
>> the required attributes of an event (which in my opinion must be a
>> timestamp,
>> at least) and how do you access them (necessary for temporal
>> relationships)?
>> Having said this, in my opinion defining an empty event interface
>> may not be
>> sufficient; in addition, it must force the user to implement a method
>> returning
>> the event's occurrence date (i.e. the timestamp) at least... Or
>> how would
>> you
>> handle this issue?
>>
>> Matthias
>>
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>
>
> Felipe Piccolini M.
> felipe.piccolini at bluesoft.cl
>
>
>
>
>
> _______________________________________________
> rules-dev mailing list
> rules-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-dev
>
>
>
>
>
> --
> Edson Tirelli
> Software Engineer - JBoss Rules Core Developer
> Office: +55 11 3529-6000
> Mobile: +55 11 9287-5646
> JBoss, a division of Red Hat @ www.jboss.com
> _______________________________________________
> rules-dev mailing list
> rules-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-dev
Felipe Piccolini M.
felipe.piccolini at bluesoft.cl
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