Unified Modeling Language Reference Manual, The, Second Edition

Event

An event is a type of noteworthy occurrence that has a location in time and space. It occurs at a point in time; it does not have duration. Model something as an event if its occurrence has consequences. When we use the word event by itself, we usually mean an event descriptor—that is, a description of all the individual event occurrences that have the same general form, just as the word class means all the individual objects that have the same structure. A specific occurrence of an event is called an occurrence. Events may have parameters that characterize each individual event occurrence, just as classes have attributes that characterize each object. Events can be divided into various explicit and implicit kinds: signal events, call events, ...