UML PSM

UML Protocol State Machines

• always defined in the context of a classifier (e.g. a class or interface)
• specifies which operations of the classifier can be called in which state and under which condition
• states of protocol state machine cannot have entry, do and exit behaviors
• protocol state machines cannot have history and deep history pseudo states
• transitions of protocol state machines cannot have effects
• transitions have [precondition]trigger/[postcondition]:

• classifier operations not represented in a protocol state machine do not have an impact on state
• protocol conformance defined explicitly via ProtocolConformance (specific state machine, general state machine tuple)