ECE 355: Software Engineering
Bridge Material
Object Oriented Design
1
Overview
What is OO Analysis & Design?
• Vending Machine Example
– Analysis
• Use case modeling
• Domain modeling
• Behavioral modeling
– Design
• Interaction diagrams
• Refined class diagram
• Concurrency and scheduling
• Summary and Further Reading
2
OO Analysis & Design
• Analysis
– Domain level - modeling “real world” objects
– Really: part of requirements engineering
• requirements development = elicitation + analysis +
specification
– Many domain objects will not make into the design
– Domain structures usually make poor design structures
• Design
– Assigning responsibilities to object
– Taking “illities” (maintainability, reusability, etc.) and
portability into account
– Devising mechanisms
3
OO Analysis & Design
• Many methods (OMT, Booch, Unified
Process, etc.)
• Similar goals and techniques
4
OO Analysis Activities
• Use case analysis
– Mostly focused on writing text - one overview context diagram is
often enough
– Use cases are just a part of functional requirements (only the
interactive ones)
• Structural analysis – domain modeling
– Finding the “real-world” objects involved in the use cases and
creating class diagrams to represent them
• Behavioral analysis
– Creating activity diagrams and sequence diagrams to capture use
case details
• Activity diagrams for business workflow
• Sequence diagrams for reactive behavior (also with timing)
– Possibly creating state charts to capture external reactive behavior
of the system and other domain objects
5
OO Design Activities
• Creating interaction diagrams and distributing
responsibilities
– Devising mechanisms and introducing design objects
– Creating sequence diagrams
– Creating collaboration diagrams
• Creating refined class diagrams
• Deciding on concurrency and scheduling model
• Possibly modeling detailed behavior of design
objects using state charts
6
Overview
• What is OO Analysis & Design?
• Vending Machine Example
– Analysis
Use case modeling
• Domain modeling
• Behavioral modeling
– Design
• Interaction diagrams
• Refined class diagram
• Concurrency and scheduling
• Summary and Further Reading
7
Use Case Diagram As a Context
Diagram
Vending Machine
Customer
Use Case 1
(Buy a drink)
8
Use Case Diagram As a Context
Diagram
Vending Machine
Customer
Use Case 1
(Buy a drink)
Use Case 2
(Restock)
Agent
9
Different Forms of Use Cases
• “Casual version”
– User story
– A narrative
• Fully dressed
– Formal sections
•
•
•
•
Preconditions
Main scenario
Exception list
…
• See “Writing effective use cases” by Alistair
Cockburn, 2000
10
Use Case 1 (“Casual Version”)
Consider a simplified vending machine, which is used to dispense soft
drinks. The vending machine consists of a coin slot for inserting coins, a
return tray for returning the customer's money and three buttons used to
select Pepsi (tm), Coke (tm) or Dr. Pepper (tm). If the customer inserts
coins and does not press a button within one minute, the coins will be
returned automatically (no coin-return lever). If the customer selects a
beverage which is out-of-stock (none left), the coins will also be returned.
This vending machine does not provide change - it is up to the customer to
insert only enough money to purchase a drink. If sufficient coins are
inserted and a button with available beverages is pressed, the appropriate
drink is dispensed, the corresponding button is illuminated for five
seconds, and the coin slot moves the coins to the general storage area (i.e.
the purchase has finished).
11
Use Case 1 (“Fully Dressed” Version)
Primary actor: Customer
Goal in context: Customer buys a drink
Level: User level
Stakeholders and Interests:
Customer : wants to buy a drink
Vendor: wants to get paid for any goods dispensed
Preconditions: Machine is ready & awaiting interaction
Minimum guarantee: Customer gets his coins back if no drink dispensed
Success guarantees:
Customer has the drink; vending machine has the money for the
drink; Vending machine provides no change
Trigger: Customer starts interaction with the machine
12
Use Case 1 (Cont’d)
Main success scenario:
1.
Customer inserts sufficient money into the coin slot
2.
Customer pushes one of the three select buttons
3.
The selected drink is dispensed.
4.
The pushed select button lights up for 5 seconds.
5.
Coins are taken by the machine.
Extensions
1a. Customer inserts no or insufficient money. Pushing a selection button has
no effect.
2a. Customer fails to push a button within 1 minute from insertion of the last
coin. Coins are returned.
2b. Customer selects beverage out of stock. Coins are returned.
Frequency of use: several per day
Priority: 1
Implementation status: …
Open issues: …
13
Overview
• What is OO Analysis & Design?
• Vending Machine Example
– Analysis
• Use case modeling
Domain modeling
• Behavioral modeling
– Design
• Interaction diagrams
• Refined class diagram
• Concurrency and scheduling
• Summary and Further Reading
14
Noun analysis
Consider a simplified vending machine, which is used to dispense soft
drinks. The vending machine consists of a coin slot for inserting coins, a
return tray for returning the customer's money and three buttons used
to select Pepsi (tm), Coke (tm) or Dr. Pepper (tm). If the customer inserts
coins and does not press a button within one minute, the coins will be
returned automatically (no coin-return lever). If the customer selects a
beverage which is out-of-stock (none left), the coins will also be returned.
This vending machine does not provide change - it is up to the customer to
insert only enough money to purchase a drink. If sufficient coins are
inserted and a button with available beverages is pressed, the appropriate
drink is dispensed, the corresponding button is illuminated for five
seconds, and the coin slot moves the coins to the general storage area (i.e.
the purchase has finished).
15
Domain Model - Initial Class Diagram
Inserts
coins
into 
Contains
CoinSlot
amount
1
1
Contains
1
1
Customer
Pushes
3
Button
id
litUp
1
Vending
Machine
1
Shelf
1 0..*
Drink
Contains
1
Contains
3
Contains
1
ReturnTray
16
Overview
• What is OO Analysis & Design?
• Vending Machine Example
– Analysis
• Use case modeling
• Domain modeling
Behavioral modeling
– Design
• Interaction diagrams
• Refined class diagram
• Concurrency and scheduling
• Summary and Further Reading
17
Sequence Diagram for Use Case 1
(Main Scenario + Extensions 1a & 2b)
customer
machine
insertMoney(x)
insertMoney(y)
push(z)
m:=checkAmount(x+y)
a:=checkAvailability(z)
[!a] return()
[m&a]
5 sec
dispenseDrink()
lightUp()
moveCoins()
lightDown()
18
Activity Diagram for Use Case 1
(Main Scenario + Extension 1a)
Customer
VendingMachine
Insert money
Select drink
money
Sufficient
money?
no
yes
Dispense drink
drink
19
State Chart for Vending Machine
(Full behavior)
Push button Z
[no drink Z]/
return money
Insert money (x)
after (60 seconds)/
return money
Ready
Push button Z [sufficient
money & drink Z in stock]
after (5 seconds)/light down
Dispensing
Entry/
dispense drink,
light up button,
take money
20
Hierarchical State Chart
Insert money (x)
Coin slot
empty
Push button Z [sufficient
money & drink Z in stock]
Coin slot
has money
after (60 seconds)/return money
Push button Z [no drink Z]/return money
after (5 seconds)
Dispensing
Entry/
dispense drink,
light up button,
take money
21
Overview
• What is OO Analysis & Design?
• Vending Machine Example
– Analysis
• Use case modeling
• Domain modeling
• Behavioral modeling
– Design
Interaction diagrams
• Refined class diagram
• Concurrency and scheduling
• Summary and Further Reading
22
Sequence Diagram
customer
coinSlot
button1
controller
shelfRel1
shelfSens1
insertMoney(x)
insertMoney(y)
push()
request(1)
close()
m:=checkAmount()
getTotal()
a:=checkAvailability()
isEmpty()
[!a] return()
[m&a]
lightUp()
release()
moveCoins()
5 sec
open()
lightDown()
23
Extension 2a
customer
coinSlot
button1
controller
insertMoney(x)
set(60)
insertMoney(y)
set(60)
timer
60 sec
checkTime()
checkTime()
timeOut()
return()
insertMoney(x)
set(60)
insertMoney(y)
set(60)
< 60 sec
push()
request(1)
close()
reset()
24
Collaboration Diagram
2: push()
button1
2.1: request(1)
timer1
1.1: set(60)
2.1.1.1: reset()
2a: timeOut()
coinSlot
1: insertMoney(x)
2.1.1: close()
2.1.2.1: getTotal()
2.1.4a [!a]: return()
2.1.7 [m&a]: moveCoins()
3.1.1: open()
2.1.5 [m&a]: lightUp()
3.2.2: lightDown()
2.1.4 [m&a]: release()
shelfRel
controller
2.1.3.1: isEmpty()
«self»
2.1.2: m:=checkAmount()
2.1.6: set(5)
2.1.3: a:=checkAvailability()
3: timeOut()
shelfSens
timer2
25
Additional Design Technique: CRC Cards
• CRC (class-responsibilitycollaborator) cards
– Index cards
– Written in a design session
– Focus on assigning
responsibilities
– Can be used in addition to
interaction diagrams
– Pioneered by ward
Cunningham & Kent beck
26
Overview
• What is OO Analysis & Design?
• Vending Machine Example
– Analysis
• Use case modeling
• Domain modeling
• Behavioral modeling
– Design
• Interaction diagrams
Refined class diagram
• Concurrency and scheduling
• Summary and Further Reading
27
Refined Class Diagram
Timer
CoinSlot
amount: Integer
opened: Bool
insertMoney(Int)
close()
open()
getTotal()
return()
moveCoins()
1
3
ShelfSens
empty: Bool
isEmpty()
1
1
1
Button
id: Integer
litUp: Bool
push()
lightUp()
lightDown()
set()
reset()
checkTime()
Signals
timeOut()
1
3
1
Controller
price: Integer
request(Integer)
checkAmount()
checkAvailability()
1
1
ShelfRel
3
release()
28
Overview
• What is OO Analysis & Design?
• Vending Machine Example
– Analysis
• Use case modeling
• Domain modeling
• Behavioral modeling
– Design
• Interaction diagrams
• Refined class diagram
Concurrency and scheduling
• Summary and Further Reading
29
Single Thread With Passive Objects
• Requires a top level control loop
– Read input, compute, write output
• Calls to procedures performing the processing
steps need to be scheduled manually
• Simple: no synchronization of concurrent threads
or processes necessary
• May waste computing resources
– “Polling style”
30
Passive objects design with a
main control loop
// main control loop
while(true)
{
If (coinSlotSensor.coinInserted())
coinSlot.insertMoney(coinSlotSensor.amount()) ;
If (buttonSensor1.pressed()) button1.push();
If (buttonSensor2.pressed()) button2.push();
If (buttonSensor3.pressed()) button3.push();
timer1.checkTime();
timer2.checkTime();
}
31
Active Objects
• Define a statechart for each object
• Communication through signals
– E.g., SDL: asynchronous send, synchronous receive
– Synchronous communication requires sending a request
and waiting for the response
– Avoid variables shared between processes
• No direct support by most programming languages
– Need a framework/library
• Better utilization of computing resources
• Automatic scheduling
32
Overview
• What is OO Analysis & Design?
• Vending Machine Example
– Analysis
• Use case modeling
• Domain modeling
• Behavioral modeling
– Design
• Interaction diagrams
• Refined class diagram
• Concurrency and scheduling
Summary and Further Reading
33
Summary
• Analysis
– Use case analysis - writing user stories
– Structural analysis/domain modeling - finding “real-world” objects
– Behavioral analysis
• Creating activity diagrams and sequence diagrams to capture use case
details
• Creating state charts to capture external reactive behavior of the
system and other domain objects
• Design
–
–
–
–
Creating interaction diagrams and distributing responsibilities
Creating refined class diagrams
Deciding on concurrency and scheduling model
Possibly modeling detailed behavior of design objects using state
charts
34
Further Reading
• Recommended OO Analysis & Design
book:
– Applying UML & Patterns: An Introduction to
Object-Oriented Analysis and Design and the
Unified Process” by Craig Larman, 2nd edition,
Prentice Hall, 2002
35