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Modeling System Behavior. 1. 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.

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state transition diagrams
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

state transition diagrams an example
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

state transition example cont d
State Transition Example (cont’d)

idle

trigger

action

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

activity
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

dialog maps
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

dialog maps as finite state machines
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

dialog maps an example
Dialog Maps – An Example

start

1

request to

cancel registration

access

denied

transaction terminated

cancellation

confirmed

cancellation

not allowed

Registration

Information

Accessed

Error

Message Displayed

Cancellation

Performed

Cancellation

Denied

cancellation

request

update submitted

update not

allowed

try again

cancellation

data

invalid

Route

Request

Modeling User Interaction to Cancel a Seminar Registration in the Seminar Registration System we worked on earlier.

9

dialog maps an example1
Dialog Maps – An Example

start

1

request to

cancel registration

access

denied

transaction terminated

cancellation

confirmed

cancellation

not allowed

Registration

Information

Accessed

Error

Message Displayed

Cancellation

Performed

Cancellation

Denied

update submitted

update not

allowed

try again

cancellation

data

invalid

cancellation

request

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

activity1
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.

12

slide13

Print

Vendor

eval_request

Attendee

Email 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

Accounts

Payable

venue_pmt_info

venue_reserved

Seminar

Administrator

venue_options

instructor_pmt_info

venue_choice

class_roster

no_venue_avail

available_instrs

Seminar

Registration

System

final_roster

Instructor Info

venues_available

inst_scheduled

inst_dates

scheduled

dates_avail

Venues Info*

email_address

roster_sign-in

Instructor

* Transfer/Maintenance TBD

final_roster

Attendee Info*

dialog maps as abstraction of user interface
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

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dialog maps and prototypes
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

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