[rules-users] Identify Rule on Attributes

[Scott Reed]

Nikil,
  What I said about the missing map entries still holds true but listen 
to Wolfgang. Since you are concerned with efficiency, using eval() and a 
map is a very inefficient approach.
     Scott

Wolfgang Laun [3/19/2009 9:09 AM] wrote:
> It appears that you want to reason about travel bookings or some such 
> thing.
>
> You are thinking of the various attributes as individual (abstract) 
> things that
> have a designation (such as "Adult Fare") and a value, with the intent to
> handle this with a set of facts, each of which has these two fields. While
> this "property list" view of data may have its merits, it complicates 
> the writing
> of rules in system like Drools.
>
> Moreover, keeping this data in a map is fine from the Java point of 
> view, but it
> leads to complications while processing it in DRL rules. (To say nothing
> about the poor performance due to eval all over the place.) I'm not sure
> about the relation between your Java class RuleAttributes and the
> HashMap instance hmAttriList, but even if the latter were an instance
> of the former (so it is a subclass of HashMap), it is questionable what
> the $a.Values["..."] returns - most likely not an Integer, and this is
> confirmed by the compiler's error message.
>
> Try to view a Booking as a Java Bean with attributes
> int numberOfAdults
> int numberOfChildren
> int childFare
> int adultFare
> boolean rejected
> and any other attribute of a booking you might want to put there.
>
> Create an instance of this bean and add it to Working Memory.
>
> A rule could now be written as
>
> rule "adt_chld_fare"
> no-loop true
> when
>     $b: Booking( $af : adultFare, childFare > ($af - 1500) )
> then
>     modify( $b ){ setRejected( true ); }
> end
>
> There are many possible variations on this. Here is just one idea:
>
> You might not want to have the rejection being stored in the Booking bean,
> so you could, perhaps assert an instance of another suitably composed Bean
> class Rejection
>     Booking booking
>     String    reason
>
> Much of the design depends on what and how you need to get the results
> of rule firing back to the application, so I won't continue.
>
> -W
> On Thu, Mar 19, 2009 at 7:52 AM, Nikhil_dev <k.nikhil at verchaska.com 
> <mailto:k.nikhil at verchaska.com>> wrote:
>
>
>     i have combined all the rules into a single RuleBase,
>     below is the content of drl file,
>
>     package com.vtech.ruleengine.module.rulemanagermodule
>     import com.vtech.ruleengine.module.rulemanagermodule.RuleAttributes;
>     import java.util.Map;
>
>     rule  "adt_chld_fare"
>     dialect "mvel"
>     when
>            $a : RuleAttributes()
>            eval ($a.Values["Adult Fare"]> ($a.Values["Child Fare"]+
>     1500 ) )
>     then
>             ($a.Values["AcceptRejectFilter"]='Reject')
>     end
>
>
>     rule  "DEMO_RULE"
>     dialect "mvel"
>     when
>            $a : RuleAttributes()
>            eval ($a.Values["Adult Fare"]> 8000 )
>     then
>             ($a.Values["Nett Payable"]= ($a.Values["Adult Fare"]* 0.80 ) )
>     end
>
>
>     rule  "Compare_date_1"
>     dialect "mvel"
>     when
>            $a : RuleAttributes()
>            eval ('12-Jan-2009'>='15-Jan-2008')
>     then
>             ($a.Values["Adult Fare"]= 5000 )
>     end
>
>
>     rule  "Rule_20090106_1"
>     dialect "mvel"
>     when
>            $a : RuleAttributes()
>            eval ( ($a.Values["No Of Adults"]< 10 ) && ($a.Values["No Of
>     Adults"]> 5 ) )
>     then
>             ($a.Values["Adult Fare"]= ($a.Values["Adult Fare"]+ -50 ) )
>     end
>
>
>     rule  "Rule_20090107_Markup"
>     dialect "mvel"
>     when
>            $a : RuleAttributes()
>            eval ($a.Values["markupPerc"]>= 0 )
>     then
>             ($a.Values["markupAmount"]=
>     ($a.Values["buyingAmount"]*$a.Values["markupPerc"]) )
>     end
>
>
>     rule  "Sample_Rule"
>     dialect "mvel"
>     when
>            $a : RuleAttributes()
>            eval ($a.Values["Sector"]< 0 )
>     then
>             ($a.Values["Via"]= ($a.Values["Via1"]+ 1250 ) )
>     end
>
>     i am passing following hashmap containing,
>     hmAttriList.put("Adult Fare", 8000);
>     hmAttriList.put("Child Fare", 80);
>     hmAttriList.put("Gross Fare", 0);
>     hmAttriList.put("Published Fare", 0);
>
>     while executing it i am getting following error message
>     SEVERE [global]
>     org.mvel.CompileException: could not perform numeric operation on
>     non-numeric types: left-type=null; right-type=java.lang.Integer
>            at
>     org.mvel.math.IEEEFloatingPointMath.doOperationNonNumeric(IEEEFloatingPointMath.java:149)
>            at
>     org.mvel.math.IEEEFloatingPointMath._doOperations(IEEEFloatingPointMath.java:102)
>            at
>     org.mvel.math.IEEEFloatingPointMath.doOperation(IEEEFloatingPointMath.java:43)
>            at org.mvel.util.ParseTools.doOperations(ParseTools.java:810)
>            at
>     org.mvel.ast.BinaryOperation.getReducedValueAccelerated(BinaryOperation.java:21)
>            at
>     org.mvel.ExecutableAccessor.getValue(ExecutableAccessor.java:45)
>            at
>     org.mvel.ast.Substatement.getReducedValueAccelerated(Substatement.java:24)
>     .............
>     ..............
>     ==>[ActivationCreated(0): rule=adt_chld_fare;
>     tuple=[fid:1:1:com.vtech.ruleengine.module.rulemanagermodule.RuleAttributes at 14a0fe1]
>     ]
>     Error Message : org.mvel.CompileException: could not perform numeric
>     operation on non-numeric types: left-type=null;
>     right-type=java.lang.Integer
>
>
>
> ------------------------------------------------------------------------
>
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