1. Modeling System Behavior1

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 2
© The KTP Company, 2005 2

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). 3
© The KTP Company, 2005 3

4. State Transition Example (cont’d)
trigger
action
idle
print request
ready new job
job complete
stop printing
new job
initiate print
ready
resume job
initiate print
paper loaded
ready resume job
printing
out_of_paper
no paper
display paper msg
jam corrected
ready resume job
jammed
display jam msg
jammed 4
© The KTP Company, 2005 4

5. State Transition Diagram for ATM

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. 6
© The KTP Company, 2005 6

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) 7
© The KTP Company, 2005 7

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 8
© The KTP Company, 2005 8

9. Dialog Maps – An Example1
start
request to
cancel registration
access
denied
transaction terminated
cancellation
confirmed
cancellation
not allowed
Registration
Information
Accessed
Error
Message Displayed
Cancellation
Performed
Cancellation
Denied
cancellation
data
invalid
try again
cancellation
request
update submitted
update not
allowed
Route
Request
Modeling User Interaction to Cancel a Seminar Registration in the Seminar Registration System we worked on earlier. 9
© The KTP Company, 2005 9

10. Dialog Maps – An Example1
start
request to
cancel registration
access
denied
transaction terminated
cancellation
confirmed
cancellation
not allowed
Registration
Information
Accessed
Error
Message Displayed
Cancellation
Performed
Cancellation
Denied
cancellation
data
invalid
try again
cancellation
request
update submitted
update not
allowed
Route
Request
Possible Application for a Decision Tree/Table
Modeling User Interaction to Cancel a Seminar Registration in the Seminar Registration System we worked on earlier. 10
© The KTP Company, 2005 10

11. Another Version of a Dialog Map

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 diagram for this system on the next slide to refresh your memory about it if needed. 12
© The KTP Company, 2005 12

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

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 14
© The KTP Company, 2005 14

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 15
© The KTP Company, 2005 15