Assessing the DCI approach to preserving use cases in Code: Qi4J and beyond

DCI (Data, Context and Interaction) comes from role-based programming and separates the system state from its behavior making it possible to preserve use cases in code to the great extent. In its Java implementation, DCI relies on the Qi4J (renamed to Apache Zest at the time of finalizing this paper) framework for role injection. This paper provides an assessment of DCI via its Qi4J implementation and beyond based on an independent study of a small car dealer system development. Two most important conceptual findings are that roles can reduce inheritance and decrease maintainability and that generic roles can be played by objects of inappropriate classes. The findings specific to the Qi4J implementation include loss of the direct domain model access from the generic context roles, entities defining their casting rules, use of interfaces instead of classes as templates for objects, no access management of the data class attributes and methods, and no direct support of polymorphism.