TABLE OF CONTENTS This chapter describes concepts needed to model behavior in terms of the flow of inputs, outputs, and control using an activity diagram. An activity diagram is similar to a traditional functional flow diagram with many additional features to precisely specify a behavior.
In SysML, an activity is a formalism for describing behavior that specifies the transformation of inputs to outputs through a controlled sequence of actions. The activity diagram is the primary representation for modeling flow-based behavior and is analogous to the functional flow diagram that has been widely used for modeling systems. Activities provide enhanced capabilities over traditional functional flow diagrams, such as the inherent capability to express their relationship to the structural aspects of the system (e.g., blocks, parts), and the ability to model continuous flow behaviors. The semantics of activities are precise enough to enable them to be mapped to executable constructs in an execution environment. However, the mapping itself has not been standardized as of this time, although there are current efforts under way to do this.
Actions are the building blocks of activities and describe how activities execute. Each action can accept inputs and produce outputs, called tokens, on their pins. These tokens can correspond to anything that flows such as information or a physical item (e.g., water). Although actions are the leaf or atomic level of activity behavior, a certain class of actions, termed call actions, can invoke other activities that can be further decomposed into other actions. In this way, call...
