[rules-users] Accessing collections in conditional statements (inside/outside working memory)

[Swindells, Thomas]

The key difference of using collections over working memory is what happens when you update a fact.
When you use update/modify you tell drools that that object has changed. Drools then works out which rules are affected by the change and re-computes the affected part of the rule and triggers them as necessary.  If you are reasoning off a list then when the object containing the list is updated all the rules that depend on the list has to be re-evaluated from scratch, even if the change didn't actually affect the list.
If you use working memory then drools can manage the lists of matching values internally and actually know which individual item has changed.  It depends on the nature of your rules and what you are doing as to whether the performance difference is a big issue or not, if you aren't modifying the objects then I don't believe it will make a significant difference.  If you are modifying the objects I'd make the children have a reference to their parent and reason using joins of that.

Are you wanting the below rules to fire once per child or just once? If it is the latter use "exists" so that it is only fired once and is likely to require less processing.

Thomas


> -----Original Message-----
> From: rules-users-bounces at lists.jboss.org [mailto:rules-users-
> bounces at lists.jboss.org] On Behalf Of Evert Penninckx
> Sent: 18 June 2010 08:13
> To: rules-users at lists.jboss.org
> Subject: [rules-users] Accessing collections in conditional statements
> (inside/outside working memory)
>
>
> Hi
>
> I'm having trouble understanding how collections are accessed in conditions
> and what this means in terms of perfomance. My app has concepts with a
> unidirectional composite relation. Making it bidirectional, as suggested in
> other posts, is really not preferred. This is the most natural model for
> this business.
>
> declare Parent
>       children : Collection // Collection<Child>
> end
>
> declare Child
>       anAttribute : String
> end
>
> With this set-up, I can think of only two rules to check for the existence
> of a child and only one to check for the absence (without starting to check
> for the size of a populated list, which seems farfetched and unreadable):
>
> rule "01 - Parent has child - using contains"
>       when
>               $child : Child( )
>               Parent( children contains $child )
>       then
>               // do stuff
> end
>
> rule "02 - Parent has child - using from"
>       when
>               $parent : Parent( )
>               Child( ) from $parent.children
>       then
>               // do stuff
> end
>
> rule "03 - Parent does not have child - using from"
>       when
>               $parent : Parent( )
>               not Child( ) from $parent.children
>       then
>               // do stuff
> end
>
> 1) Is the cost of the "contains" in rule 01 the same as the "from" in rule
> 02? Why (not)? If so, inserting the Child facts in the working memory seems
> not necessary.
> 2) I read in other posts and the user guide that putting all facts in
> working memory should be faster. Is it correct to say, that the perfomance
> gain will only be achieved when not using the "from" CE and thus only by
> using a bi-directional relation between Parent and Child?
>
>
> In any case, it seems to me that stuffing child objects into working memory
> shouldn't be the concern of a client calling a "rule service". So should
> this be more optimal, I'd make the rules insert the facts using an
> agenda/ruleflow to make sure everything is inserted before doing the
> business stuff.
>
>
> Greetz
>
> -Evert
>
>
> ---
> If you are posting a question, please try search first. Your question may
> have already been answered.
> Don't post repeatedly. Wait for a few days. People will read your post by
> email.
>
> --
> View this message in context: http://drools-java-rules-
> engine.46999.n3.nabble.com/Accessing-collections-in-conditional-statements-
> inside-outside-working-memory-tp905005p905005.html
> Sent from the Drools - User mailing list archive at Nabble.com.
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> rules-users at lists.jboss.org
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