Executable Protocol Models as a Requirements Engineering Tool

Functional prototypes and simulations are a well recognized and valued tool for building a shared understanding of requirements between users and developers. However, the development of such artifacts does not sit well with traditional modeling techniques, which do not lend themselves to direct execution. Consequently building prototypes and simulations becomes a diversion from the mainstream development process, and sometimes even competes with it. We propose that the resolution to this conflict lies in promoting the role of executable behavioral models, so that artifacts supporting behavioral simulation are a by-product of the mainstream modeling process. We discuss why conventional modeling techniques are not suited to this, and we describe an innovative behavioral modeling technique, Protocol Modeling, that is well suited to direct execution. Using Protocol Modeling, a behavioral entity (business object or process) is modeled in terms of its event protocol: the conditions under which it accepts or refuses events. Such models capture the behavioral integrity rules at the level of business events; and can be composed using the semantics of Hoare's CSP, allowing concise and incremental representation. Direct execution of the model is achieved using a tool that simulates a normal user interface, so that non-technical stakeholders can review and explore behavior while requirements are being solidified.