![]() A call event, in general, is synchronous. A call event may trigger a state change in a state machine. In UML, we model the relationship between an operation and the events using a dependency stereotyped with “send”, which indicates that an operation sends a particular signal.Ī call event represents the dispatch of an operation from one object to another. ![]() The execution of an operation can also send signals. ![]() A signal may be sent as the action of a state in a state machine or as a message in an interaction. Exceptions are the famous examples for signals. In UML, we can model four kinds of events namely: signals, calls, passing of time and change in state.Ī signal is a named object that is sent asynchronously by one object and then received by another. For example, a overflow exception generated by an object is an internal event. Internal events are those that are passed among objects living inside the system. For example, in an ATM system, pushing a button or inserting a card are external events. Events passed between the system and its actors are external events. Signals may be represented as stereotyped classes and other events are represented as messages associated with transitions which cause an object to move from one state to another.Įvents may be external or internal. UML allows us to represent events graphically as shown below.
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