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Activity Diagram - Revisited

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  1. Activity Diagram - Revisited C-S 546

  2. Activity Diagram • Also called an “activity graph”, is a variation of a state machine representing actions and subactivities • Remember the difference between “activity” and “action” in UML • Activity : A sequence of actions that take finite time and can be interrupted • Action: An atomic task that cannot be interrupted (at least from user’s perspective) C-S 546

  3. Activity Diagram (continued) • Transitions in an activity diagram do not have labels • They indicate the completion of an action or subactivity and show the sequence of actions or subactivities • Consequently, these transitions are not based on external events • An activity diagram may describe a use case, an operation or a message • Purpose: to describe implementation-oriented details C-S 546

  4. Activity Diagram – Basic Syntax Action 1 Action 2 Action 3 Action 4 [C] [~C] split merge C-S 546

  5. Activity Diagram - semantics • Each action state must have a label; otherwise, no information is conveyed by that action state • A transition can be split (see the vertical bar) into multiple transitions that can reach multiple action states • These transitions occur concurrently; in the previous diagram, “Action 2” and “Action 3” said to occur concurrently, after “Action 1” C-S 546

  6. Activity Diagram – Semantics (continued) • Two or more transitions can be combined together using a merge (the same vertical bar notation) • The destination after the merge can be reached ONLY AFTER the source actions are completed • In the previous diagram, if “Action 4” is invoked, the entire activity terminates ONLY AFTER “Action 2” and “Action 4” complete C-S 546

  7. Activity Diagram – Semantics (continued) • An outgoing transition from an action state may end up in a condition box (a diamond symbol) and hence will be split into 2 or 3 transitions • The conditions must be MUTUALLY EXCLUSIVE • Action state labels may represent methods and hence may include parameters C-S 546

  8. [No coffee] [No cola] Find Beverage [found cola] [found coffee] Put Coffee in Filter Add Water Get Cups Get cola can(s) Put filter in M/c Switch on M/c Wait until brewed Drink Pour into cup Preparing Beverages - ©UML Manual version 1.5 C-S 546

  9. false amount > 0 report error true false balance  amount amount – balance  N false report error true true balance = balance - amount Use case “withdraw” with overdraft protection ‘N’ represents overdraft limit C-S 546

  10. Subactivity An action state in an activity diagram can be represented by a subactivity as shown below Subactivity A subactivity represents a simplification of another activity diagram It reduces the space for an activity diagram C-S 546

  11. Subactivity - semantics • A subactivity is a representation of another activity diagram • The incoming arrow to a subactivity matches with the initial state of the activity diagram represented by the subactivity • The outgoing arrow from a subactivity matches with the final state of the activity diagram represented by the subactivity C-S 546

  12. Swimlanes • Several activity diagrams can be merged into one diagram • particularly to show the interacting actions between these diagrams • Each activity diagram is enclosed in a separate box and the boxes are joined together in the swimlane diagram • See the example in the next slide C-S 546

  13. Customer Sales Stockroom Request service Take Order Pay Fill Order Deliver order Collect order C-S 546

  14. Objects as parameters • Objects passed as parameters between action states can be represented in the activity diagram (and in swimlane diagram) using the same syntax for objects • The transition between an object parameters and an action state is represented with a dashed line, instead of a solid line C-S 546

  15. Customer Sales Stockroom Request service : Order [placed] :Order [entered] Take Order Pay Fill Order : Order [filled] :Order [delivered] Deliver order Collect order C-S 546