1. 1 Modeling System Behavior

2. 2 State Transition Diagrams A state transition diagram is a model that depicts a system’s states and the events that cause the system to change states. A state is any observable mode of behavior for the system. The state transition diagram also shows what actions are taken as a consequence of an event Such models are often called finite state machine models

3. 3 State Transition Diagrams – An Example Following is a state transition diagram for software controlling a printer. In this simplified model, we’ve identified five distinct states: idle, ready, printing, jammed, out_of_paper. The arrows represent transitions from one state to another. Along each arrow we note the event triggering the state change (above the horizontal rule) and the action taken in response to the event (below the horizontal rule).

4. 4 State Transition Example (cont’d) printing ready out_of_paper jammed display jam msg jam corrected ready resume job new job initiate print resume job initiate print job complete stop printing idle print request ready new job no paper display paper msg paper loaded ready resume job trigger action

5. State Transition Diagram for ATM

6. 6 Activity Consider the software that controls the functions of a cruise control device on an automobile. Work with your team to create a state transition diagram for this system. The particular device we’re working has the usual cruise control functions, plus the following enhanced ones: 1) if your vehicle pulls within 50 feet of a vehicle in front of you, an active cruise control device will turn itself off if it is set for more than 45 mph; 2) when you tap the brake once, the cruise control speed is suspended, but may be reinstated by pressing the resume button; 3) if you tap the brake more than once or if you hold the brake down for more than 2 seconds, the cruise control device will turn itself off in which case the speed setting is cancelled and will have to be reset when you re-engage the device.

7. 7 Dialog Maps User interfaces can often be regarded as a finite state machine model Thus, state transition diagrams can be used to model these Such state transition diagrams are referred to as dialog maps (also sometimes called site maps when used with Web development)

8. 8 Dialog Maps as Finite State Machines Each dialog element (menu, screen, dialog box, etc.) can be viewed as a state The user can then navigate to another dialog element (i.e. change states) The possible elements and the navigation paths between them can be modeled as a state transition diagram

9. 9 Dialog Maps – An Example cancellation request Route Request update submitted update not allowed try again cancellation data invalid Modeling User Interaction to Cancel a Seminar Registration in the Seminar Registration System we worked on earlier. Registration Information Accessed Cancellation Performed cancellation confirmed Cancellation Denied request to cancel registration cancellation not allowed Error Message Displayed transaction terminated access denied 1 start

10. 10 Dialog Maps – An Example cancellation request Route Request cancellation confirmed request to cancel registration cancellation not allowed update submitted update not allowed try again cancellation data invalid transaction terminated access denied 1 start Possible Application for a Decision Tree/Table Modeling User Interaction to Cancel a Seminar Registration in the Seminar Registration System we worked on earlier. Registration Information Accessed Cancellation Performed Cancellation Denied Error Message Displayed

11. Another Version of a Dialog Map

12. 12 Activity Consider the Seminar Management System we’ve been working on. Work with your team to create a dialog map that models the seminar administrator’s interactions with the system in obtaining an instructor for a seminar. Refer to the Context for this system on the next slide to refresh your memory about it if needed.

13. Proposed Seminar Management System SMS Seminar Administrator venue_request venue_options venue_choice instructor_request no_instructor_available instructor_reserved request_for_eval Email Sys Selected Venue booking_request booking_confirmation eval_request class_roster Accounts Payable venue_pmt_info instructor_pmt_info Instructor Info * Transfer/Maintenance TBD Attendee completed_eval seminar_completed Attendee Info* available_instrs inst_scheduled roster_sign-in Instructor dates_avail scheduled final_roster email_address Seminar Registration System Venues Info* inst_dates venue_reserved no_venue_avail venues_available Print Vendor seminar_notification booking_denied final_roster

14. 14 Dialog Maps as Abstraction of User Interface Dialog maps can be viewed as high-level abstractions of user interfaces Show the dialog elements and navigational links among them They do not reveal, or even take into account, detailed screen designs or data field definitions

15. 15 Dialog Maps and Prototypes A dialog map makes a good preliminary model to use before beginning the construction of a prototype Provides vehicle for a high-level discussion with users about the interface functionality -- without getting bogged down in screen appearance and data definition details Excellent model for discovering missing requirements and misunderstood requirements relative to user interactions