[rules-users] In drools what is the exact difference between Insert and Update ??

[Bhushan]

Hey Luane Thanks a lot man... I wlll keep all these points as a Best
Practices in my notes.Do u have any material Which talks about best
practices and it's example in drools.If yes could you please share with me
on my mail id @bhushansonaje at gmail.com.Actually We don't have any drool
expert in our project who know's all these things.

*Luane* Ones again Thanks 




laune wrote
> 
> Hi Bhushan,
> 
> some amendments to Davide's comments.
> 
> Salience: You might argue for one (1) rule (per class) with low
> salience to detect a fact (of that class) that failed to be processed
> (similar to the "default" in a switch).
> 
> Globals: In LHS *only* for introducing *constant* data, to compare to
> fact data. In RHS code where the global is an object providing a
> service, e.g., to send a matched fact to some external processor,
> store it in a DB or whatever.
> 
> RHS all in Drools: Using Java static methods for certain tasks has the
> benefit that they are easier to unit test.
> 
> UPDATE: You must use update (or, preferably, modify) if, and only if,
> you have to change your facts AND changed facts must be processed by
> other rules. - There is a scenario where you might invoke setters on a
> fact object but you do not intend that the modified field is ever
> processed by a rule: then do not call update/modify.
> 
> However, you might also design your system in a way where you do not
> update/modify primary facts. Instead, to keep track of truths
> discovered by
> your rules, you insert new (secondary) facts of types according to
> your design, linking them to your primary fact.
> 
> rule discover
> when
>     $p: Primary( color == Color.GREEN, shape == Shape.ROUND )
> then
>    insert( new RoundAndGreen( $p ) )
> end
> 
> rule process
> when
>      $p: Primary()
>      $rag: RoundAndGreen( primary == $p )
> then
>     process(...)...
>     retract(...),...
> end
> 
> HTH
> -W
> 
> On 28/03/2012, Davide Sottara <dsotty@> wrote:
>> Dear Bhushan, the recommendations you got from your architect should be
>> intended as best practices, not as strict instructions. Indeed, it
>> depends
>> on what kind of rules you are writing and their business logic.
>>
>> I agree that functions and globals should not be abused, and that
>> salience
>> and groups should be intended as execution constraints, not as
>> fine-grained
>> flow control, but I would reason on a case-by-case basis.
>>
>> Now, as far as "update" is concerned... update is NEEDED to let the
>> engine
>> know that some fact has changed. The only way not to use update is NOT TO
>> LET FACTS CHANGE. This is hardly possible in dynamic systems.
>> In that case, the only alternative is to replicate and insert the facts
>> with
>> different state identifiers (e.g. timestamps): Person( name=david, age=25
>> ),
>> Person( name=david, age=26 ), Person( name=david, age=27 ).....
>> This is indeed a purely declarative approach, which you pay with
>> additional
>> logic - to select only the "current" facts - and additional memory
>> consumption.
>> If the reason for not using update is that rules fire when they
>> shouldn't,
>> then I agree that no-loop is not the best choice. It works only for the
>> same
>> rule where you do the update, so it's hardly a safe way to proceed.
>> I would suggest, instead, to add constraints preventing the modified
>> version
>> of the fact to trigger rules which have already fired. If you could
>> provide
>> an example with one of your use cases, it would be easier to discuss the
>> pros and cons
>> Best
>> Davide
>>
>> --
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