[rules-users] Correlation of events

[Edson Tirelli]

   Ashfaq,

   The idea of a rules engine is that all the "search", or in better 
words, the "match" of facts is done in the LHS. This is exactly what the 
rules engine does better! The RHS should be composed (ideally) of simple 
actions, not algorithms.

   For instance, in your example, lets say you use 2 other fields for 
correlating the events: source (the origin of the error) and type (the 
type of the error).
   Your rule would simply be written:

rule "new error"
when
    $error : Error( state == NEW_ERROR, $source : source, $type : type )
    $errFromWorkingMemory : Error( source == $source, type == $type )
then
    $errFromWorkingMemory.setLastTimeStamp( currentTimestamp );
    modify( $errFromWorkingMemory );
    retract( $error );
end

   See? Clean and clear. No algorithms involved and the engine will 
optimize the matching and execution giving you the best performance.
   You can also create rules to automatically remove any error with 
status NEW_ERROR that is not the last one, based on timestamp. Example

rule "keep only the last error"
when
   $error : Error( $state : state == NEW_ERROR, $source : source, $type 
: type, $timestamp : timestamp )
   exists Error( state == $state, source == $source, type == $type, 
timestamp > $timestamp )
end
   retract( $error );
end

   So, my advice is: use the engine to your benefit... ;)

   []s
   Edson

Steven Williams wrote:

> I think you may want to use a global here:
>
> global ErrorMetaData errorMetadata;
>
> rule "new error"
>         when
>                 $error : Error (state == NEW_ERROR)
>         then
>                 (search workingmemory if this error was already 
> registered)
>                 if (found)
>                 {
>                         errorMetadata.setLastTimestamp(currentTimestamp)
>                         retract($error);
>                 }
> end
>
>
> On 2/28/07, *Framewala, Ashfaq Y* <Ashfaq.Framewala at gs.com 
> <mailto:Ashfaq.Framewala at gs.com>> wrote:
>
>     Hi,
>
>     I am working on a system where I need to correlate few error
>     conditions happening in the network infrastructure. I have gone
>     through the documentation for Jboss rules engine (Drools) and I am
>     planning to use it for the correlation purpose.
>
>     Can anyone let me know a way in which I can get an object from
>     workingmemory in the "then" part of the rule? For e.g., I need the
>     following
>
>
>     rule "new error"
>             when
>                     $error : Error (state == NEW_ERROR)
>             then
>                     (search workingmemory if this error was already
>     registered)
>                     if (found)
>                     {
>                            
>     $errFromWorkingMemory.setLastTimestamp(currentTimestamp)
>                             retract($error);
>                     }
>     End
>
>     Thanks,
>     Ashfaq
>
>                    
>                                    
>
>
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>
>
>
> -- 
> Steven Williams
>
> Supervising Consultant
>
> Object Consulting
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-- 
 Edson Tirelli
 Software Engineer - JBoss Rules Core Developer
 Office: +55 11 3124-6000
 Mobile: +55 11 9218-4151
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