Control flow based state model

Control flow based state model generation relies on the implicit flow of control among use case events and the explicit flow of control among use cases as specified by follow lists coupled with enabling directives.

At the use case level, UCEd generates a StateChart-Chart. A UML activity diagram with use cases as nodes. The following is a StateChart-Chart generated by UCEd as shown by the state model viewer.

Figure 5.1: Generated StateChart-Chart.

A StateChart-Chart includes control flow nodes (join, fork, merge, decision) that capture use case sequencing constraints expressed by follow lists and enabling directives.

The details of each use case can be shown by double-clicking on the use case node. Each use case corresponds to a StateChart. Statecharts are useful for reactive behavior model description. A StateChart is defined as a tuple [$Trig_{c}$, $Reac_{c}$, $G_{c}$, $S_{c}$, $S0_{c}$, $F_{c}$].

• $Trig_{c}$ is a set of triggers. $Trig_{c}$ includes operations from the environment and timeout events.
• $Reac_{c}$ is a set of reactions that are operations executed by the system.
• $G_{c}$ is a set of guard conditions.
• $S_{c}$ is a set of states. The followings are notable characteristics of StateCharts states.
  • Hierarchical states: a state may have super-states and sub-states. A system is in a state s is concurrently in all the sub-states of s.

    Any transition starting from a state s also applies to all the sub-states of s.

  • Parallel states: a system may be in several unrelated states at a same time.
• $S0_{c} \in S_{c}$ is the initial state of the statechart.
• $F_{c}$ is a transition function in domain . Each transition includes a start state s, an optional trigger trig, a set of guards g, a set of reactions reac and an ending state $s^{\prime}$.

The following shows the StateChart-Chart with all use cases StateCharts displayed.

Figure 5.2: Generated control flow based state chart. We do not represent transitions details to avoid cluttering the graph. Transitions details can be seen by hovering over.

Generated StateCharts includes states and transitions representing use case interactions. A transition to a use case state (or a flow node) corresponds to an enabling directive. Such a transition results in the system entering the use case initial state.