If you are starting from scratch, this is possible. However, I find myself having to expose operations from the *preexisting* technical domain into the business (i.e expose methods from existing technical domain code that has all kinds of annotations and code references to 3rd party software). The only way out, in that case, is to have your own separate business domain classes that wrap around (proxy) the existing technical domain



From:        Wolfgang Laun <wolfgang.laun@gmail.com>
To:        Rules Users List <rules-users@lists.jboss.org>
Date:        01/20/2012 06:36 AM
Subject:        Re: [rules-users] Declarative fact model or Java?
Sent by:        rules-users-bounces@lists.jboss.org

---

Let me mention that I've used Java classes derived from XML Schema
as facts.

If there are technical properties you'd like to hide from the rule programmer,
define a "business" type and extend it with the technical properties. The
rule programmer must make do with the "business" type, which is
possible even if the object (fact) type is the "technical" subclass.

-W


On 20/01/2012, Stephen Masters <stephen.masters@me.com> wrote:
> Hi Davide,
>
> Thanks for your thoughts. The application is just a service which takes an
> XML request, converts that into a fact and inserts that into the working
> memory. Based on rule evaluations, it responds to the client with more XML
> indicating whether the requested action is permitted.
>
> On of the key aims of the project is to enable management of some rules by
> 'the business' through Guvnor. The current 1-1 mapping you mention is partly
> what put me off using Java models, as it leads to 'technical' attributes
> being present in the Guvnor fact model, which are not relevant to the
> business. The more I can keep the fact model within Guvnor minimal, the
> better.
>
> So following your logic, given that:
> There is no legacy model to deal with.
> ~80% of what is going on will be within Drools, with the Java code just to
> insert/update facts and marshal XML.
> I would really like to avoid a 1-1 mapping of Java classes to DRL facts.
> ... I think I'll stick with DRL facts.
>
> Given that I'm not too sure exactly what I want out of it yet, I'm not sure
> how much I could contribute to a spec, but I'd be happy to help out with
> things. If only by testing out early code and providing feedback. If there's
> anything you think I might be able to help out with, feel free to ping me an
> email.
>
> Many thanks,
>
> Steve
> stephen.masters@me.com
>
>
> On Jan 20, 2012, at 11:44 AM, Davide Sottara <dsotty@gmail.com> wrote:
>
> Hi Steve,
> let me share my thoughts on this.
>
> You will probably want to use a Java model when it's already available :) Or
> when you're using the rule engine to implement the business logic layer of
> your application, processing data coming from an external source.
>
> A DRL model, instead, is definitely recommended for "temporary" facts, or
> data structures which are used by the rules to do their computations.
> The main problem with DRL fact classes is that they're quite cumbersome to
> use outside the rule engine. On the other hand, you will be sure that the
> declared types will correspond to an implementation fully compatible and
> optimized for the rule engine.
>
> Very roughly : if the rule engine is a component in a larger architecture,
> use java classes. If you're building a rule-based application - i.e. DRL is
> your programming language and Drools is your execution environment, go for
> DRL.
>
> As for mapping, we have added this very experimental feature lately:
>
> http://blog.athico.com/2011/12/new-feature-spotlight-traits-part-1.html
> http://blog.athico.com/2011/12/dynamic-typing-in-rules-traits-part-2.html
>
> I have plans to use annotations to improve the mapping, avoiding the 1-1
> correspondence between fields, so if you want to contribute, if only to the
> specifications, let us know :)
>
> Best
> Davide
>
> --
> View this message in context:
> http://drools.46999.n3.nabble.com/rules-users-Declarative-fact-model-or-Java-tp3675001p3675181.html
> Sent from the Drools: User forum mailing list archive at Nabble.com.
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