Correct me if I'm wrong, I would summarize your requirements as follows:
- you need some "A-box" reasoning, but you are fine with a rule-based approach
- the object-oriented integration Drools provides is quite convenient
- you have large data sets for which an opportunistic, "query-oriented" approach
would work better rather than a fully generative "forward chaining" approach

Drools "hybrid-chaining" approach could be very useful here - I'm not sure how
well documented it is, and how you are planning to use it, but it would be interesting
to see one of your rules - even "stripped" of the details you don't want to show -
to discuss the behaviour of the engine and its implications.

I had a use case apparently very similar to yours some time ago.. I'm working even
now on some experimental forms of rule/object/ontology integration. The "trait"
feature might be an alternative to the explicit addition of classes to objects .. it was
enhanced a few days ago to support updates and modifications.
If you have an ontology to begin with, you might also be interested in the ontology -> class
conversion tool I'm working on even now

Davide

On 04/12/2013 01:45 AM, Upali Kohomban wrote:

Hi,

Sorry for the late reply, I was away from mail.

I'm fine with assumptions such as unique name and closed world because whatever method I use these handicaps will be there in some form. In my case, why I can't go on with OWL/Logic is the issue of large amounts of factual data which change frequently, unlike, say, in Biomedical ontologies.

For an instance, I want to model the semantics of a country's appeal as a holiday destination for a particular crowd depending on any events that makes it interesting for that crowd. These things can change on day-to-day basis depending on weather, currency rates, school holidays, ticket prices etc. OWL ontologies (as you must know) handle these kind of volatile data quite poorly. Unfortunately, its difficult to plug things to the reasoner at the facts-end of the OWL. This last bit is different for Drools.

On the other hand, as I said, the number of possible inferences are near infinite, and unnecessary unless they are explicitly queried. For instance take a transitive relationship such as situated_in(x, y). If there are few levels of locality (say, country/district/city/town/suburb) there will be so many unnecessary inferences for the relationship in drools rules. With a backward chaining reasoner, these inferences won't fire unless queried.

According to my limited understanding of drools, this is the main issue one could come up against using drools here. I was trying to work around that fact by using the (apparently recent) backward-chaining queries, and by delegating some of the worse (transitive etc) clauses to POJO. I really enjoy being able to do that, even if I'm doing it wrong and there's a better way ;-)

So far, I'm using a mix of technologies to get what I think is the best of both worlds: backward-chaining, POJO for logic itself at lower level for recursive rules, semantic classes to "store" inferences about stuff so they can be queried later.

If there is a better way of doing this, I'd really love to know it. I'm aware that this is not ideal problem for an expert system or an ontology. However I need to model a little bit of semantics than a database-only system, and do it in an easily changeable way.

Thanks,
Upali

On 12/04/2013 00:56, Davide Sottara wrote:

Ontology Reasoners and Rule Engines are quite different, can be integrated under some assumptions,
but are definitely not easily interchangeable.. (unique name assumption, closed world assumption, etc..)
Which one is better pretty much depends on the use case, which also dictates the required level of
expressiveness of the language - even Fact++, Hermit and Pellet do not support full FOL...

This said, your case seems very interesting.. would you mind sharing a few more details or a concrete example?
We would then be able to assess whether Drools is appropriate or not, and which constructs could be
used (e.g. traits, hybrid chaining queries, tms, ...) to tackle the complexity.

Or maybe we could take it as a use case to improve the engine capbilities :)

Best
Davide

On 04/11/2013 05:01 AM, Upali Kohomban wrote:

Thanks a lot again, you made my life easy with the build instructions :)

Yes I'm trying to do an integration. I have some experience with ontologies and want to experiment with drools as an alternative.

OWL with reasoners like Fact ++ are pretty much good for the job, except for the fact that they handle individual data bits in quite a cumbersome way. It was because of this reason that I wanted to experiment on other ways of modeling a knowledge structure with better facilities for querying large amounts of factual data. I'm giving drools a try, but I'm not entirely sure if drools can do things as powerful as a reasoner.

Basically, I'd like to be able to let the data lie (without firing any "events" until necessary) and query the inferences in a first-order logic like manner. This is very space-efficient in data-heavy scenarios. I know that this isn't the traditional way drools is designed to work. I'm trying to solve the inference problem by dynamically adding semantic classes to each object to store all the possible inferences about it, so they can be queried later. Problem with this approach is that it gets out of hand very quickly, because the enumerated number of such inferences can be HUGE even for a moderate KB. Backward chaining will eventually solve this problem, but it seems that the constructs available for that in drools queries are not too matured at the moment. For instance they don't seem to support numerical inequality operators (or I am wrong, which is also very likely).

Thank you again for the quick help,
Upali

On 11/04/2013 14:14, Davide Sottara wrote: