[rules-users] Beginner looking for help with some Drools/Rule concepts

[Michael Neale]

If you assert engine as a seperate fact, you can then access the engine
directly.

In the next version, you will be able to do
Car(engine.running == true) and it will be converted to a predicate (sugar)
- but always less efficient in RETE terms then accessing a field directly on
a fact.

On 1/11/07, Kabe <kabriel at gmail.com> wrote:
>
> Hi, i've been attempting to use Drools/JBossRules (3.0.5) in a project i'm
> working on and i've run into a few issues that i could use some help with.
> For the most part i'm struggling with design patterns on how to structure my
> facts and my programs object model.
>
> I'm struggling a bit with how to properly introduce my object model into
> the working memory. For example, lets say i have an object model such as:
>
>    Car(
>       Engine(
>          boolean : running
>       ) : engine,
>       color,
>       Door(
>          boolean : open
>       )[]:doors
>    )[] : cars
>
> This would model a list of cars and some fields such as engine, color, and
> doors. Now how would i create a rule that would return every car with a
> running engine? I can't seem to figure out how to correctly reference a
> field of a field of a fact. i would want to do something like Car(
> engine.running == true ) or Car( Engine( running == true ) ) but that
> doesn't work. I can't make the Engine itself a fact because it has to be a
> field of the Car, and i can't give the car a field that holds the state of
> the engine because then that breaks encapsulation and makes the Car class
> very bloated with the state of all of its many components.
>
> Is there a way to do this correctly? i could use a real messy predicate or
> something like this:
>
> $car : Car()
> eval( isCarRunning( $car ) )
>
> But then what is the point of using Rete? doesn't that just equate down to
> about the same amount of work if i just put this in some standard java
> if/else code?
>
> Thanks for the help,
>
> ....
> Kabe
>
>
>
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