Behavior Modeling

Summary

• Structural vs Behavioral
• States
• Events
• UML Event Taxonomy
• Behavioral Modeling
  • Combinatorial Modeling
    • Decision Tables
    • Decision Tree
  • Sequential Systems
    • State Transition Table
    • State Transition Diagram

Structural vs Behavioral

Structural models express properties that are always true.

Behavioral models express how the system responds to external stimuli.

States

State := abstract description of a system at a given time

State Space := set of all possible states

State space increases multiplicatively

• “State Explosion Problem”

TicTacToe has 19683 states

Events

Event := a single, instantaneous, noticeable occurrence

Events can be sync or async

• Clock-based or random

UML Event Taxonomy

• Signal
  • Async notifications
• Method Call
  • Sync operation invocation
• State Change
  • Continuously monitored
• Time Passage

Behavioral Modeling

Reactive Systems := systems that respond to events

Modeling Techniques:

• Combinatorial
  • States, but no events
• Sequential
  • States, linearly ordered events
• Concurrent
  • States, unconstrained events

Combinatorial Modeling

Expresses logic of simple combinatorial systems

Only inputs determine subsequent states, and not the history of events

Decision Tables

Conditions are called inputs, responses are called outputs

Workshop has 3 switches, 2 output devices and 1 master switch. Switches can either be on or off.

Master	Light Switch	Power Switch	Lights	Motor
ON	ON	ON	ON	ON
ON	ON	OFF	ON	OFF

$$\vdots$$

Decision Tree

Graphical form of decision table where decisions are made sequentially

Diamonds are decisions, rectangles are actions

flowchart TD M{Master Controller On} M –>|No| oo[Light Off / Motor Off] M –>|Yes| lso{Light Switch On?} lso –>|No| loffp{Power Switch On?} lso –>|Yes| lonp{Power Switch On?} loffp –>|No| loffpoff[Light Off / Motor Off] loffp –>|Yes| loffpon[Light Off / Motor On] lonp –>|No| lonpoff[Light On / Motor Off] lonp –>|Yes| lonpon[Light On/ Motor On]

Sequential Systems

Sequential systems have “memory” of previous system activities

Also called “Finite State Systems” or “Finite State Machines”

State Transition Table

Rows are states

Columns are:

• name
• input event
• output action
• next state

Current state	Input	Action	Next State
Door closed, motor off	Button pressed	Start motor	Motor running up
Motor running up	Door open detected	Stop motor	Door open, motor off
Motor running up	Button pressed	Stop motor	Door partially open, motor off
Door partially open, motor off	Button pressed	Start motor	Motor running down
Door open, motor off	Button pressed	Start motor	Motor running down
Motor running down	Door closed detected	Stop motor	Door closed, motor off
Motor running down	Button pressed	Stop motor	Door partially closed, motor off
Door partially closed, motor off	Button pressed	Start motor	Motor running up

State Transition Diagram

Graphical representation of FSM

etc.