1. A computer processing system for obtaining a value via a rule engine implemented by a collection object in an object-oriented application, said system comprising: means for receiving a request for a value from an object-oriented application, said request including a key and an invocation of a built-in method of said collection object associated with said object-oriented application, wherein said collection object is capable of storing said key, storing data associated with said key, and providing said data in response to said receiving said request; means for invoking a rule engine external to said object-oriented application by overriding said invocation of said built-in method of said collection object; means for identifying, by said invoked rule engine and responsive to said receiving and said overriding, a rule included in a rule definition file external to said object-oriented application, said identifying based on said rule being associated with said key included in said request, said rule definition file including an algorithm associated with said rule; and means for executing said algorithm by said rule engine to provide said value.