[rules-users] Dynamic object structure Drools use case?

[Tina]

I'm trying to get a handle on whether Drools is the right tool for the job
we have at hand.  Based on what I've seen in the documents and examples, I
believe it could be, but that we're definitely taking a more difficult
path.  Interested in thoughts from folks with more experience than me.

Our project is looking for a solution to let us deal with streaming data,
and determine whether each individual data item meets a rule's criteria.  Each
data item implements an interface, but the properties available on the
concrete objects differ wildly.   Also, each data item can be considered to
be composed of multiple levels of these data items.  One of the fields on
the interface is a getParent field, which returns the data item one level
up.  (In effect, we end up with a singly linked list.)  If X is the object
which we have a direct handle to, X.parent = Y, and Y.parent = Z, we often
want to look at Z.field as part of our rule.  I believe that the quirk here
is that, although the objects are JavaBeans, they are presented as an
interface which does not describe the property set of the bean.  Thus, I
don't directly know that X's parent is Y, whose parent is of type Z, which
then has a property named 'foo'.  (Beans here are essentially user-defined
structures for contributed code, and thus we have no real way of knowing
what properties are on a bean until we receive the bean.  When the users use
the beans, they obviously know which bean they're working with.  For us,
we're getting it downstream, and that bean could be any of a dynamically
growing variety, also with many different permutations of structures in the
linked list.)

As a practical matter, the interface has a method getField(String, String),
whihc allows us to access specific fields both in the local bean and in the
beans available up its list.  That functionality is accomplished through
some reflection logic.

I've tried the following approach, but it "smells" wrong:
- Create adapter classes per rule, and, given a data item, insert the item
again, adapted with a bean that gives access to the specific fields.  We
believe the # of rules will be 10 or less at any given time in the
operational system. This would require us to query the known rules, and
provide adapter classes for them, which seems completely counter to normal
patterns of use.  However, it would allow us to use a bean approach.  [Note
that although I've shown that inserting an event again has my desired
effect, I haven't yet figured out how to query the set of rules, and provide
adapter classes for each rule.]

I'm also considering a DSL approach, trying to determine if that would allow
me to somehow transform the problem.

Any insights or feedback would be wonderful.  In-house, we don't yet have a
great depth of expertise with Drools, so I'm interested in tapping a broader
pool of knowledge and experience.  I've only got access to Drools 4 in my
environment.  I can try alternate approaches in Drools 5 at home, but can't
use that solution as yet for our problem space.

- Tina
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