UML State Diagrams (Ch. 29)

State Diagrams State diagrams: Provides another dynamic view of aspects of system Expresses: Events States Behavior of an object in reaction to an event Shows behavior of an object

Fig. 29.1

State Diagrams Terminology: Event – a significant occurrence (instantaneous, has no duration) State – a condition of an object, time between events (has duration) Transition – object moves from one state to another, triggered by an event Notation for each

State Diagrams Guideline: Consider state diagrams for state-dependent objects with complex behavior Guideline: Business information systems typically have few state-dependent classes/objects Process control, device control, protocol handlers, communications systems typically have many state-dependent objects See p. 488 for examples

State Diagrams Notations: Action – an event may cause an action to fire Conditional guard – a transition may be guarded by a boolean test, the transition fires only if event occurs at a point where test is true

State Diagrams Nested states a state can contain substates substates inherit transitions of enclosing state

Applying state diagram to web page navigation State Diagrams Applying state diagram to web page navigation

State Diagrams Example from POS system: State diagram shows legal sequencing of use case operations . . .

Fig. 29.5