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