UML

1. UML Discussion on State Machines

2. Because nothing ever happens Perfectly static system is intensely uninteresting

3. Real Systems • Dynamic in nature and always something is happening internally or externally. • ATM Machine. • Robot. • Chemical Reaction. • Network Router.

4. Objects • Objects work together to realize higher-order behaviors defined by use cases. • Object Behavior with respect to time • Simple • State • Continuous

5. What is State Machine • Its abstract • It has finite state of conditions of existence called states • It has set of actions performed in each state • It has set of events which causes state change to well defined rule set.

6. State Machine Example Possible States RED YELLOW GREEN Flashing Yellow Flashing Red …

7. What things exhibit state ? • Classes • Use cases State Machine can be applied to object oriented systems as well as functionally decomposed ones.

8. Behavioral Elements

9. Guard State Machine Transition State Event

11. State Machine • Using state machine you can Model behavior of individual object. • State Machine illustrates sequential behavior of object. • Statechart Diagrams. • State to State. • Activity Diagrams. • Activity to Activity.

12. Example Payment Authorization Authorizing Rejected Authorized Delivered

13. Web Application • Not yet logged in. • Action: Display the login page • Logged in and viewing the account balance • Display the account balance • Display logout button, and view transaction button. • Logged in and viewing recent transactions • Display recent transactions • Display logout button, and view account balance button. • Logged out • Display “Goodbye page”

15. Validate Login/PIN

16. Word Processing

17. Brew Controller of coffee machine

18. Coffee Machine Tank

19. Sequential Sub states

20. Concurrent Substates

21. Food For Thought…. Identify States

22. Hypothetical State Machine • Event Queue • When event is received it is placed in queue of target • Event Dispatcher • When delivered to state machine • Event Processor • Consumed and event is complete

23. State Machine Concepts • Context • An association to the model element that whose behavior is specified by this state machine • States • Transitions • Event

24. State Machine Concepts • Context • States • models a situation during which some (usually implicit) invariant condition holds. • Transitions • Event

25. State • Simple State • No Substates • Initial State • Object comes into being • Final State • The entire state machine has completed • A final state cannot have any outgoing transitions

26. State Machine Concepts • Context • States • Transitions • A transition is a directed relationship between a source state and target state • Event

27. Transition Source Trigger Guard Target Effects

28. Guard • A guard is a Boolean expression that is attached to a transition as a fine-grained control over its firing. • If the guard is true at that time, the transition is enabled, otherwise, it is disabled.

29. State Machine Concepts • Context • States • Transitions • Event • An event is a specification of a type of observable occurrence

31. Events • Call Event • Reception of request to synchronously invoke operation. • Creation of object • Deletion of object • Time Event • Models expiration of specific deadline.

32. Events… • Signal Event • Reception of asynchronous signal

34. Events… • Change Event • Implicit • Results as a change in some value of object attribute

35. Practical Implementations • Mapping of Statechart to efficient code • Common Approaches • Double Nested Switch Statements • Action state tables • Generic state machine interpreters • State Patterns in OO Paradigm

37. /* States. */ #define IDLE 0 #define DIAL 1 #define ALERTING 2 #define CONNECTED 3 #define BUSY 4 #define RINGING 5 /* Possible inputs */ #define ON_HOOK_IND 0 #define OFF_HOOK_IND 1 #define DIGITS_IND 2 #define CONNECTED_IND 3 #define INCOMING_CALL_IND 4 #define TIMEOUT_IND 5 #define PICKUP_IND 6

38. int transtab[][] = /* transtab[Input][CurrentState] => NextState */ { /* IDLE DIAL ALERTING CONNECTED BUSY RINGING */ { IDLE, IDLE, BUSY, IDLE, IDLE, IDLE }, /* ON_HOOK_IND */ { DIAL, DIAL, BUSY, IDLE, IDLE, IDLE }, /* OFF_HOOK_IND */ { IDLE, ALERTING, IDLE, IDLE, IDLE, IDLE }, /* DIGITS_IND */ { IDLE, DIAL, ALERTING, IDLE, IDLE, IDLE }, /* CONNECTED_IND */ { RINGING, DIAL, IDLE, CONNECTED, BUSY, RINGING }, /* INCOMING_CALL_IND */ { IDLE, DIAL, BUSY, IDLE, IDLE, IDLE }, /* TIMEOUT_IND */ { IDLE, DIAL, BUSY, IDLE, IDLE, CONNECTED }, /* PICKUP_IND */ }; int curstate = IDLE; curstate = transtab[event][curstate];

39. Who defines state transitions ? MayDefineStateMachine

40. Who defines statemachine.. • Context • States Themselves • State Tables

41. Guidelines • Create A State Chart When Behavior Differs Based on State • Place The Initial State In The Top-Left Corner • Place The Final State In The Bottom-Right Corner • State Names Should be Simple but Descriptive • Question “Black Hole” States • Question “Miracle” States • Create a Hierarchy of State Charts for Very Complex Entities • Name Transition Events in Past Tense

42. What Next • Identify the implementation schemes • Use XMI • Aim for changes in statemachine which will need no or minimal changes to existing state implementations

43. Reference • http://www.uml.org

45. Thank You