[rules-users] Creating objects in WHEN clause

[Greg Barton]

If the Quantity and Duration object already exist in your application, can they be inserted into working memory automatically? (i.e. their existence can be assumed when writing the rules.)

Another option is to get them using the from keyword and an external method that generates objects. (Or optionally gets them from a map if they've alreay been created.)

rule "foo"
when
  $quantity : Quantity() from getQuantity(2, "m");
  $Person($height > $quantity.height)
then
...
end

I'm not completely sure that syntax will work as written, but you get the idea.

And, not to go too far into a philosophy discussion, but the domain expert should not be writing DRL directly if they're a non-programmer.  Actually, domain experts should not be writing rules at all.  That's the job of the knowledge engineer.  There are many complexities to consider when authoring rules.  If a domain expert is stymied by something as simple as initializing the working memory properly they're going to have a steep learning curve. 

--- On Wed, 2/25/09, David Boaz <davidb at dbmotion.com> wrote:

> From: David Boaz <davidb at dbmotion.com>
> Subject: Re: [rules-users] Creating objects in WHEN clause
> To: rules-users at lists.jboss.org
> Date: Wednesday, February 25, 2009, 1:02 PM
> Thanks,
> These Quantity and Duration objects are commonly used in
> our application. My
> concern is from the software-engineering prespective. Now,
> the rule author
> (which is supposed to be a "domain expert") has
> to maintain the information
> twice: once when inserting these objects to the working
> memory (at the
> initialization), and then when writing the concrete rules.
> Im looking for a trick to make the rule-aurhor life more
> convienient...
> 
> Greg Barton wrote:
> > 
> > I'd second this idea, and to get around the
> inconcenience of inserting the
> > Quantity objects from the calling application, use a
> rule that fires once
> > on initialization.
> > 
> > rule
> > no-loop true
> > when
> > //No condition
> > then 
> >   insert(new Quantity("m", 2));
> > end
> > 
> > This rule should fire first.  You could also put it in
> it's own
> > agenda-group (call it "initialization" or
> some such) and set focus to that
> > group when starting.
> > 
> > rule
> > agenda-group "initialization"
> > no-loop true
> > when
> > //No condition
> > then 
> >   insert(new Quantity("m", 2));
> >  
> drools.setFocus("whatever_your_next_group_is");
> > end
> > 
> > --- On Wed, 2/25/09, Mauricio Salatino
> <salaboy at gmail.com> wrote:
> > 
> >> From: Mauricio Salatino <salaboy at gmail.com>
> >> Subject: Re: [rules-users] Creating objects in
> WHEN clause
> >> To: "Rules Users List"
> <rules-users at lists.jboss.org>
> >> Date: Wednesday, February 25, 2009, 11:40 AM
> >> How about :
> >>  WHEN
> >> $quantity: Quantity(value == 2, unit ==
> "m")
> >> $Person($height == $quantity:)
> >> then
> >> ...
> >> 
> >> 
> >> 
> >> On Wed, Feb 25, 2009 at 2:27 PM, David Boaz
> >> <davidb at dbmotion.com> wrote:
> >> >
> >> > In my application, we often compare the
> fact's
> >> field values against a known
> >> > object. For example:
> >> > WHEN person(height> new Quantity(2,
> "m"))
> >> // the height is greater than 2
> >> > meters.
> >> > will DROOLS create a "singleton"
> Quantity
> >> object, or will it create one
> >> > object for each fact evaluation?
> >> >
> >> > We consider using anoter approach, using
> GLOBALS.
> >> Then, the Quantity object
> >> > will be created applicatively, and passed by
> the API
> >> to the engine.
> >> > something like:
> >> > GLOBAL Quantity 2meters
> >> > WHEN person(height > 2meters)
> >> > But this approach is combersom, because the
> rule
> >> author has to define part
> >> > of the information in the calling
> application, and
> >> part in the rule.
> >> >
> >> > Do you have a good practice how to handle
> these
> >> situations?
> >> >
> >> > Thanks, David
> >> > --
> >> > View this message in context:
> >>
> http://www.nabble.com/Creating-objects-in-WHEN-clause-tp22207616p22207616.html
> >> > Sent from the drools - user mailing list
> archive at
> >> Nabble.com.
> >> >
> >> >
> _______________________________________________
> >> > rules-users mailing list
> >> > rules-users at lists.jboss.org
> >> >
> https://lists.jboss.org/mailman/listinfo/rules-users
> >> >
> >> 
> >> 
> >> 
> >> -- 
> >>  - Salatino Mauricio -
> >> _______________________________________________
> >> rules-users mailing list
> >> rules-users at lists.jboss.org
> >>
> https://lists.jboss.org/mailman/listinfo/rules-users
> > 
> > 
> >       
> > _______________________________________________
> > rules-users mailing list
> > rules-users at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-users
> > 
> > 
> 
> -- 
> View this message in context:
> http://www.nabble.com/Creating-objects-in-WHEN-clause-tp22207616p22209417.html
> Sent from the drools - user mailing list archive at
> Nabble.com.
> 
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