[rules-users] Abstraction between rules and data model?

Tue May 27 08:57:20 EDT 2014

Hi Davide,

Drools trait functionality is one of the powerful concepts which makes
Drools a good candidate for the project. So keep up the good work! :)
However I'm not sure if its current level of flexibility would be
sufficient for our use case. I've checked the documentation, but haven't
really found the term virtual field -- could you please elaborate on this?

Do you think we could somehow hook into the evaluation of the aliases or
the "fields" Map? Sometimes you would need slightly more than merely
aliasing fields to something else; e.g. calculating values for the purpose
of rule processing or extracting a value from a more complex object tree
etc. Citing the example -- GoldenCustomer( fields[ "age" ] > 18 ) -- being
able to get a reference to the target object and the field map expression
"age" would be quite close to what I imagined. Our custom code could then
perform the appropriate translation and return the requested value, hiding
the fact whether "age" is an actual field in the Customer object
itself/retrieved from an encapsulated complex object e.g. replacing
expression "customer.personalInformation.birthData.age"/calculated on the
flight.

What do you think?

Cheers,
Peter

2014-05-26 17:58 GMT+02:00 Davide Sottara <dsotty at gmail.com>:

> We are working on the trait framework for cases like this. Essentially,
> it allows to use
> interfaces when writing rules AND to inject the interfaces dynamically
> at runtime,
> at the instance level. It relies on transparent proxies which wrap the
> data classes
> and implement the required interfaces. A simple field aliasing mechanism
> is provided
> (work in progress). For more complex transformations, "virtual" fields
> can be added.
> See section 7.7.8 of the manual for more details and let me know if it
> can help
> with your use case.
> Best,
> Davide
>
> On 05/26/2014 09:55 AM, Wolfgang Laun wrote:
> > Even a relatively sophisticated transformation would be easier to
> implement
> > and most certainly safer from changes in the unstable Drools API than
> some
> > hook-and-intercept mechanism built into Drools.
> >
> > Notice that violent structural departure of the model the BUs see from
> what
> > you call "persistence model" might make it impossible for the BUs to come
> > up with rules that can be transformed to match the other model at all;
> > if it is possible, rules might still incur a heavy performance penalty.
> >
> > It is (IMHO) a myth that "Rules" is a foolproof way of establishing
> > business logic
> > independent from the data model and application environment with which
> > this logic should be able to cooperate. As long as everything is kept in
> the
> > abstract (i.e., formulated in terms of mathematics) it will look  good,
> but
> > any implementation may throw a spanner in the works, or worse.
> >
> > -W
> >
> > On 26/05/2014, Péter Gergely, Horváth <h.peter at mailbox.hu> wrote:
> >> Hi Wolfgang,
> >>
> >> Thank you for your input. You are right that some of the cases could
> simply
> >> be covered by regexp-replace, but I'm afraid, not all of them.
> Interfaces
> >> could also help, but we have a requirement that the business rules
> should
> >> not be tightly coupled to the underlying persistence model. (I
> understand
> >> that some might say this is not ideal, but that is our current
> situation)
> >>
> >> I am wondering whether it is possible to hook into Drools engine and
> >> intercept field value reference expression evaluations in run time (e.g
> if
> >> "foo.bars" is used in an expression, we could return "foo.barList") ? By
> >> injecting some custom code, we could make the necessary decisions and
> >> extract the proper value from an object. Unfortunately these parts of
> >> Drools are pretty much undocumented.
> >>
> >> Regards,
> >> Peter
> >>
> >>
> >>
> >> 2014-05-26 13:57 GMT+02:00 Wolfgang Laun <wolfgang.laun at gmail.com>:
> >>
> >>> What you describe can be done with /bin/sed.
> >>>
> >>> Notice that the DSL processor doesn't require you to translate entire
> >>> patterns; there is a mechanism for translating "keywords", which is
> >>> just arbitrary tokens to whatever replacement text.
> >>>
> >>> If a "bar" must be translated to a "barList" in the context of a class
> >>> "Foo" but not in any other context, a more sophisticated translation
> >>> is required in any case (with /bin/sed still being sufficient if
> >>> patterns aren't split across lines).
> >>>
> >>> Some say that good design makes use of Interfaces, which leaves room
> >>> for actual implementations being changed as long as the interfaces are
> >>> implemented. Here, note that rules can be written against interface
> >>> types.
> >>>
> >>> -W
> >>>
> >>>
> >>> On 26/05/2014, Péter Gergely, Horváth <h.peter at mailbox.hu> wrote:
> >>>> Hi All,
> >>>>
> >>>> We are evaluating Drools 6 for our use case, and face challenges where
> >>>> we
> >>>> would need some ideas from more experienced users of Drools.
> >>>>
> >>>> We have an application with a massive code base and a large number of
> >>> model
> >>>> (entity) classes. We are in the process of moving away from inherited
> >>>> legacy technologies and refactoring the old code base. As a part of
> >>>> this
> >>>> work we would like extract some of the hard-coded business logic to
> >>>> external rules, that is why we are looking at Drools as a potential
> >>>> solution.
> >>>>
> >>>> What we would like to have is some kind of abstraction or mapping
> >>>> between
> >>>> actual entities and rules the business users can define so that they
> do
> >>> not
> >>>> have to know the _exact_ details of the data model (field names,
> >>>> precise
> >>>> relations etc). This would be important for us so that we can refactor
> >>> the
> >>>> old model classes without affecting business rules; also it would make
> >>> life
> >>>> easier for the business users. While IDE support might make
> refactoring
> >>>> easier, we definitely want to have a separation between rules and
> >>> entities.
> >>>> Given our situation, writing and maintaining "stable" wrapper/adapter
> >>>> classes for the sole purpose of rule processing is out of question. I
> >>> have
> >>>> checked the documentation of Drools DSL support and for me it seems to
> >>>> be
> >>>> overkill for our use case: we do not really need a custom language,
> but
> >>>> simply an abstraction between rules and the data model classes.
> >>>>
> >>>> What I could imagine is a piece of code, (a custom property resolver?
> -
> >>> no
> >>>> sure how it is called) which maps property expressions to actual
> >>> properties
> >>>> based on a custom annotation on the entity class or something like
> >>>> that,
> >>> so
> >>>> that a rule containing "Foo.bars" expression does not have to change
> >>>> even
> >>>> if we decide to rename "Foo.bars" to "Foo.barList" in the model
> >>>> classes.
> >>>> (This was just a simple example of a potential use cases)
> >>>>
> >>>> Could you please share your thoughts on this topic and point me into
> >>>> the
> >>>> right direction?
> >>>>
> >>>> Thanks,
> >>>> Peter
> >>>>
> >>> _______________________________________________
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> >>> rules-users at lists.jboss.org
> >>> https://lists.jboss.org/mailman/listinfo/rules-users
> >>>
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