Modeling the Dynamic Behavior of Objects On Events, Messages and Methods

Events messages and methods are concepts supported by most object oriented analysis and design techniques The interrelation between these concepts is however not yet fully understood and guide lines and techniques for method speci cation remain unprecise and in complete In this paper we provide a simple object model which we use both to clarify the above interrelation and to devise a method for spec ifying the dynamic behavior of objects In a two layered approach this method integrates the description of the object s life cycles with the spec i cation of the object s methods Our object model is characterized by two important assumptions namely that methods are virtual objects and that messages sent to inexistent objects are returned back as an error Both assumptions are supported by practical evidence and allow us to model internal concurrency multiple threads and attribute sharing in a very simple and elegant way Our ideas are illustrated on a simple banking example