Wolfgang I use patterns like that for a data filtering problem and also for a preferential selection problem. Any time I have two sources of the same data and I prefer one over the other that pattern allows you to pick the secondary source when the preferred data doesn’t exist. Also used in cases where we want to execute a different action in the absence of the second source.

It also occurs for us when dealing with a list of objects where we have two sources for the same type of data and we prefer one data source over the other, but we don’t always get data for the preferred source.. We use your pattern to make sure the preferred source doesn’t exist before using the secondary source

Joe

Here is an example from our code. $ebs is a List<Map>. Mapping to your example the Map is the fact and the combination of BnftInfoCdoe and BnftCvgeLevelCode would be the field.:

  Map(this[BenefitsConsts.BenefitResponseEligibility.BnftInfoCode] == 'C',

this[BenefitsConsts.BenefitResponseEligibility.BnftCvgeLevelCode] == 'IND',

this[BenefitsConsts.BenefitResponseEligibility.SvcTypeCode] == "30",

this[BenefitsConsts.BenefitResponseEligibility.CvgePeriodQlfr] == '25',

this[BenefitsConsts.BenefitResponseEligibility.BnftAmt] matches "0.*") from $ebs

not (Map(this[BenefitsConsts.BenefitResponseEligibility.BnftInfoCode] == 'C',

this[BenefitsConsts.BenefitResponseEligibility.BnftCvgeLevelCode] == 'FAM') from $ebs)

From: rules-dev-bounces@lists.jboss.org [mailto:rules-dev-bounces@lists.jboss.org] On Behalf Of Wolfgang Laun
Sent: Thursday, March 24, 2011 11:07 AM
To: Rules Dev List
Subject: [rules-dev] An odd couple of patterns

Has anybody ever seen a situation where a couple of patterns such as

   Fact( field >= 10 )
   not Fact( field > 20 )

was appropriate? This does not match Facts where field isn't between 10 and 20, and so it would seem to be the same as

   Fact( field >= 10 && <= 20 )

but actually it doesn't match any such Fact whenever any other Fact with field > 20 is around.

Cheers
Wolfgang