I can
turn that question around...
If the
user has written objects MyFact and MyEvent is it fair to expect them to
have to declare it in the DRL?
I don't
know what Events are to do in Drools so don't which is the more reasonable
approach. Is it just for network optimisation as you say, or will Drools be
calling into members?
This is
much more interesting than (my) work ;-)
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@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@lists.jboss.org
[mailto:
rules-dev-bounces@lists.jboss.org] On Behalf Of Matthias
Sent: 08
November 2007 13:09
To: rules-dev@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