Chapter 10 - Modeling Message-Based Behavior with Interactions

Abstract

This chapter discusses the use of sequence diagrams to model how parts of a block interact by exchanging messages. Behavior was modeled using activity diagrams to represent a controlled sequence of actions that transform inputs to outputs. This chapter presents an alternative approach to representing behavior. This approach uses sequence diagrams to represent the interaction between structural elements in a model as a sequence of message exchanges. The interaction can be between the system and its environment or between the components of a system at any level of a system hierarchy. A message can represent the invocation of a service on a system component or the sending of a signal. This representation of behavior is useful when modeling service-oriented concepts, when one part of a system requests services of another part. A service-oriented approach can represent discrete interactions between software components, when one software component requests a service of another and when the service is specified as a set of operations. However, the sequence diagram is not limited to modeling interactions between software components and has found broad application in modeling system-level behaviors. An interaction can be written as a specification of how parts of a system should interact and can also be used as a record of how the parts of a system do interact.