Decision modules in models and implementations

Abstract

We define a type of concern called a decision module. Decision modules can be seen as a specific subset of often changeable business rules, identified in requirements. We present decision modules as protocol machines in protocol models. The proven property of such protocol machines is their unidirectional dependency from other protocol machines. The composition technique used in protocol models allows for such local changes in a protocol machine that the behaviour of unchanged machines in the whole system is preserved. We analyse different Java implementation techniques in order to find the possibility of building decision modules having the same properties as in protocol models. We implement decision modules using object composition, reflection, the publisher-subscriber design pattern, interceptors and aspects. The results of our experiments are illustrated with an example of a document submission system. We discuss the functionality of a generic library that we build for adopting the new style of locally changeable implementations with separated decision modules.