Principles of
Engineering System Design
Dr T Asokan
[email protected]
Principles of
Engineering System Design
GRAPHICAL MODELLING
TECHNIQUES
Dr T Asokan
[email protected]
BEHAVIOR MODELING
Method used for exploring the dynamics of the system.
Address the discrete-event behavior, which is behavior that
is triggered by the occurrence of specific events.
• Control, activation, and termination of system
functions
• Ex:
FFBD ( Functional Flow Block Diagrams),
Behavior diagrams, Petrinets
FFBDs provide a hierarchical decomposition of the
systems function and show a control structure that
dictates the order in which the function can be
executed at each level of the decomposition.
• Series, Concurrent, selection, and multiple exit
Petri Nets
• First introduced by Carl Adam Petri in 1962.
• A diagrammatic tool to model concurrency
and synchronization in distributed systems.
• Used as a visual communication aid to model
the system behaviour.
• Based on strong mathematical foundation.
• Captures precedence relations and structural
interactions of potentially concurrent and
asynchronous events.
A Petri Net Specification ...
• consists of three types of components: places
(circles), transitions (rectangles) and arcs (arrows):
– Places represent possible states of the system (P=
p1,p2,….)
– Transitions are events or actions which cause the change
of state (T=t1,t2…); And
– Every arc simply connects a place with a transition or a
transition with a place.
The state of PN is defined by the marking.
p1
p2
t1
Asokan T ED 309
A Change of State …
• is denoted by a movement of token(s)
(black dots) from place(s) to place(s); and is
caused by the firing of a transition.
• The firing represents an occurrence of the
event or an action taken.
• The firing is subject to the input conditions,
denoted by token availability.
t1
Asokan T ED 309
A Change of State
• A transition is firable or enabled when there
are sufficient tokens in its input places.
• After firing, tokens will be transferred from
the input places (old state) to the output
places, denoting the new state.
Asokan T ED 309
Example: EFTPOS System (A Petri net)
(EFTPOS= Electronic Fund Transfer Point of Sale)
1 digit
Initial
1 digit
d1
1 digit
d2
1 digit
d4
d3
OK
OK
OK
OK
OK
OK
pressed
Rejected!
Reject
approve
approved
Asokan T ED 309
EFTPOS System
• Scenario 1: Normal
– Enters all 4 digits and press OK.
• Scenario 2: Exceptional
– Enters only 3 digits and press OK.
Asokan T ED 309
Example: EFTPOS System (Token Games)
1 digit
Initial
1 digit
d1
1 digit
d2
1 digit
d4
d3
OK
OK
OK
OK
OK
OK
pressed
Rejected!
Reject
approve
approved
Asokan T ED 309
Example: Vending Machine
• The machine dispenses two kinds of snack
bars – Rs 20 and Rs 15.
• Only two types of coins can be used
– Rs 10 coins and Rs 5 coins.
• The machine does not return any change.
Asokan T ED 309
Example: Vending Machine (A Petri net)
Take Rs 15 bar
Deposit 10
5
15
Deposit 5
Deposit
5
0
Deposit
5c
Deposit 10
Deposit
5
20
10
Deposit 10
Take Rs 20 bar
Asokan T ED 309
Example: Vending Machine (3 Scenarios)
• Scenario 1:
– Deposit 5, deposit 5, deposit 5, deposit 5, take Rs
20 snack bar.
• Scenario 2:
– Deposit 10, deposit 5, take Rs15 snack bar.
• Scenario 3:
– Deposit 5, deposit 10, deposit 5, take Rs20 snack
bar.
Asokan T ED 309
Example: Vending Machine (Token Games)
Take Rs 15 bar
Deposit 10
5
15
Deposit 5c
Deposit
5
0c
Deposit
5
Deposit 10
10
Deposit
5
20
Deposit 10
Take Rs 20 bar
Asokan T ED 309