[rules-dev] Determining if a class is an event or not

[Edson Tirelli]

   Michael,

   Yes, the session.insertEvent() API is something other engines (like iLog
JRules) have. I initially discarded that idea, but since you mentioned, we
may need to reconsider it.
   Anyway, the API would solve this part of the problem, but the whole
scenario is:
   The engine must know at the compile time exactly what classes/interfaces
used in rules are events, so that it can optimize the network. That is
achievable by using any of the syntaxes bellow (I'm not sure which one to
use yet):

import event a.b.c.Foo; (or)
import event a.b.c.*;

or explicit saying:

declare event a.b.c.Foo;

    Once the user declared that something is an event, do you think it is
fair/acceptable to force the user to use a different API to insert events
into the engine?

session.insert(); for regular facts
session.insertEvent(); for events

   []s
   Edson

2007/11/8, Anstis, Michael (M.) <manstis1 at ford.com>:
>
> 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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>
>


-- 
  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
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