Rule Builder > Business Rule Checks > Check Rule Consistency > Report Rule Subsumptions

A business rule is said to subsume another, if the conditions of the subsumed rule are included in the conditions of the subsuming rule. There are two types of subsumption:

Subsumption is a probable consequence of redundancy.

Unconditional Rule Subsumptions

Any object that matches the subsumed rule (or group of objects, if the rule matches several objects) will also match the subsuming rule. The following two BAL rules, MoreThan100 and MoreThan1000, cause a warning of this type. See Figure 14.7 for the warning text.

In this example, the MoreThan100 rule subsumes the MoreThan1000 rule, because if the value is greater than 1000 it will also be greater than 100.

MoreThan100 Rule

 If 
         the purchase value is greater than $100
 Then
         apply a 10% discount

MoreThan1000 Rule

 If 
         the purchase value is greater than $1000
 Then
         apply a 20% discount

Potential Rule Subsumptions

Potential rule subsumption happens when the subsuming rule contains conditions concerning classes that are not tested in the subsumed rule. The rule is considered to be subsumed, provided that the extra conditions of the subsuming rule are not incompatible with the subsumed rule.

In the following two BAL rules, MoreThan1000 and MoreThan500Gold, consistency checking reports that the first rule is potentially subsumed by the second rule. See Figure 14.7 for the warning text.

The subsumption is true because any shoppingCart matched by the MoreThan500Gold rule is matched by the MoreThan1000 rule, since a value greater than 500 may also be greater than 1000. However, in this case there is potential subsumption due to the second condition on Customer, which may or may not be true.

MoreThan1000 Rule

 If 
         the purchase value is greater than $1000
 Then
         apply a 20% discount

MoreThan500Gold Rule

 If
         the purchase value is greater than $500
         and the customer category is Gold
 Then
         apply a 15% discount

images/check_subsumption.png

Figure 14.7    Rule Subsumption

See Also

Business Rule Structure | Checking Rule Consistency


Customer Support | Copyright © 1987-2004 ILOG S.A. All rights reserved. Legal terms. PREVIOUS   NEXT