ISBN : 978-81-963532-2-3 (E-Book) Activitydiagramsvs.proceduralflow charts Activity diagrams are similar to the procedural flow charts. The difference is that activity diagramssupportdescriptionofparallelactivitiesandsynchronizationaspectsinvolvedindiffe rentactivities. STATECHARTDIAGRAM A state chart diagram is normally used to model how the state of an object changes in its lifetime.State chart diagrams are good at describing how the behavior of an object changes across several usecase executions. However, if we are interested in modeling some behavior that involves severalobjects collaborating with each other, state chart diagram is not appropriate. State chart diagrams arebasedon the finite statemachine (FSM)formalism. A FSM consists of a finite number of states corresponding to those of the object being modeled. Theobject undergoes state changes when specific events occur. The FSM formalism existed long beforethe object-oriented technology and has been used for a wide variety of applications. Apart frommodeling,ithasevenbeenusedintheoreticalcomputerscienceasageneratorforregularlan guages. A major disadvantage of the FSM formalism is the state explosion problem. The number of statesbecomes too many and the model too complex when used tomodel practical systems. This problemis overcome in UML by using state charts. The state chart formalism was proposed by David Harel[1990]. A state chart is a hierarchical model of a system and introduces the concept of a compositestate(alsocalled nested state). Actions are associated with transitions and are considered to be processes that occur quickly and arenotinterruptible.Activitiesareassociatedwithstatesandcantakelonger.Anactivity canbeinterruptedbyan event. Thebasicelementsofthestatechartdiagramareasfollows: Initialstate-Thisisrepresentedasafilledcircle. Software Engineering Keerthana P, Manasa KN, Ganga D Bengal 77
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