An Experience in Architectural Extensions: Active Objects in J2EE

In this paper we present an experience in architectural extension. The goal of our project was to provide Active Objects in the Java 2 Enterprise Edition (J2EE) reference architecture by suitable extensions that should not violate the architectural J2EE principles. Our approach to the problem was rather formal. We first formalized the notion of Active Object, the basic characteristics of the J2EE model and its component model Enterprise JavaBeans (EJB). Then, driven by the peculiar characteristics of an active object, we investigated several possible architectural extensions. The solutions were formalized as well and their consistency with the J2EE model was validated by using model checking techniques. In this way we discovered that only one of them was acceptable. The whole formalization and validation has been carried out by using the Charmy environment. In Charmy the architectural formalization makes use of diagrammatic notations, Scenarios and State Diagrams, and SPIN is the target model checking engine.