Subject: Object Oriented Modeling and Design

Difficulty: Medium

Marks: 4 Marks

• Concurrent state diagram shows a set of independent behaviors of an object.
• Concurrent sub states are independent and can execute in parallel. A state may be divided into regions containing sub-states that exist and execute concurrently.
• UML shows concurrency within an object by partitioning the composite state into regions with dashed lines.

Example:-

• In the above example, concurrent sub states are shown. Maintenance is a composite state. It is decomposed into two concurrent sub-states as testing and commanding.
• Each of these concurrent sub-states is further decomposed into sequential sub-states.
• When control passes from Idle to Maintenance state, control then forks to two concurrent flows.
• Execution of these two concurrent sub-states continues parallel in the system. Each nested state machine reaches its final state.
• If one concurrent sub state reaches its final state before the other, then control in that sub-state waits at its final state.
• When both nested state reaches their final state, control from the two concurrent sub-states joins back into one flow.