[rules-users] How many KnowledgeBases?

[Greg Barton]

Agenda groups seems to fit.  They are used to specify what mode of processing you're in and what rules fit that mode.  The "{handwave handwave}" in that case is not arcane, it's a setFocus() call on the agenda. :)  And there's only two ways the system can know what mode it must be in: 1) There's some detectable condition that triggers said mode (as in the example you linked to) or, 2) you tell it explicitly. (As in a setFocus() call before you fire the rules.)

And yes, you'd no doubt have to hide the syntax from the business user with a DSL, unless you want them learning drools syntax.

Also, you've mentioned some alternatives and how they don't feel right to you.  What would be the structure of a solution that would feel right?

There is another alternative: use control facts.  This approach is useful if you want to process many modes at the same time.  Rules would look like this:

rule "Foo"
when
  Mode(name="pricing", t : target) 
  $product: Product(this == t)
  ...other conditions...
then
  ...stuff...
end

The Mode would be a class with String name and Object target members.  When inserting the Product working memory you'd also insert a Mode with name "pricing" that pointed to the Product.  So the Mode object is a fact that is used solely for control of rule flow.

The DSL for rules could look like this

We're in Pricing Mode (translates to "Mode(name="pricing", t : target)")
There's a Product (translates to "$product: Product(this == t)")
...etc, etc, etc...

This is an old school method that was used before such conveniences as agenda groups came to be and I still prefer it in some cases.

--- On Fri, 2/19/10, Laird Nelson <ljnelson at gmail.com> wrote:

> From: Laird Nelson <ljnelson at gmail.com>
> Subject: [rules-users] How many KnowledgeBases?
> To: rules-users at lists.jboss.org
> Date: Friday, February 19, 2010, 1:01 PM
> Forgive me for what I suspect is an
> elementary question.  That said, I did not see it explained
> in newcomer-friendly language in the documentation, if at
> all.  And I'm a newcomer!
> 
> I'm working on a system for--among other
> things--pricing things.  Drools Expert is a great fit for
> this.
> 
> 
> The system also has to do other things that have nothing to
> do with pricing (let's say shipping, to keep it
> simple).  There are places where Drools Expert is a great
> fit for this as well.
> 
> In both cases, let's assume I might insert a given
> product into the engine, turn the crank, and collect my
> results.  But the kinds of results I'm looking for--and
> the kinds of calculations I would expect to be
> performed--are quite different in each case.
> 
> 
> So, let's assume that--naively speaking here--when I
> insert the product and {handwave handwave} I
> "know" I'm doing pricing work, then I only
> need pricing-related rules to fire (I don't need the,
> say, product-color-determining rules to fire, or the
> can-the-product-be-shipped-to-Abu-Dhabi rules to fire, or
> the how-many-people-liked-this-product rules to fire,
> etc.).
> 
> 
> And when I insert the product and {handwave handwave} I
> "know" I'm doing--whatever--shipping work,
> then I don't need the pricing rules to even be
> considered.
> 
> I found this (http://n3.nabble.com/Grouping-rules-td55531.html#a55531)
> as perhaps one way of creating different sets of rules to be
> evaluated in different contexts.  This smelled very arcane
> to me for this purpose, but...? perhaps it's the way to
> go?
> 
> 
> Another is obviously to create n KnowledgeBases, each with its own set of
> rules, where n is the number of contexts or
> activities or types of activities that I'm performing. 
> Then I'd look up the (pre-created) KnowledgeBase
> appropriate for the particular calculation I need
> performed.  That seems like solving the problem with a
> crowbar, a length of iron pipe and a blowtorch.  Ick.
> 
> 
> Is there an accepted/preferred way to handle this sort of
> thing?  Agenda-groups seem...well, perhaps they'd work,
> but it seems awfully arcane for something that I was hoping
> would be a little more end-user friendly.  Quoting the
> Expert manual:
> 
> 
> When Should You Use A Rule Engine?
> [...]
> Domain experts often possess
> a wealth of knowledge about 
> business
>           rules and processes. They typically are
> nontechnical, but can 
> be
>           very logical. Rules can allow them to express the
> logic in 
> their own
>           terms. Of course, they still have to think
> critically and be 
> capable
>           of logical thinking.
> 
> My domain users would almost certainly not think in terms
> of agenda groups.  Perhaps I could hide this in a DSL or
> something, but it seems to me there must be some facility
> built into Drools for separating collections of rules into
> channels, or groups, or partitions, or....  Is there?
> 
> 
> Best,
> Laird
> 
> 
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