ECE 355: Software Engineering

1. ECE 355: Software Engineering Bridge Material Object Oriented Design

2. 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

3. 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

4. OO Analysis & Design • Many methods (OMT, Booch, Unified Process, etc.) • Similar goals and techniques

5. 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

6. 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

7. 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

8. Use Case Diagram As a Context Diagram Vending Machine Use Case 1 (Buy a drink) Customer

9. Use Case Diagram As a Context Diagram Vending Machine Use Case 1 (Buy a drink) Customer Use Case 2 (Restock) Agent

10. 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

11. 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).

12. 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

13. Use Case 1 (Cont’d) Main success scenario: • Customer inserts sufficient money into the coin slot • Customer pushes one of the three select buttons • The selected drink is dispensed. • The pushed select button lights up for 5 seconds. • 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: …

14. 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

15. 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).

16. Domain Model - Initial Class Diagram Inserts coins into  Contains CoinSlot amount 1 0..* 1 Contains Drink Shelf 3 1 1 Vending Machine 1 Contains 1 Customer 1 1 Button id litUp Contains Pushes 3 Contains 1 ReturnTray

17. 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

18. 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] dispenseDrink() lightUp() 5 sec moveCoins() lightDown()

19. Activity Diagram for Use Case 1(Main Scenario + Extension 1a) Customer VendingMachine Insert money Select drink money Sufficient money? no yes Dispense drink drink

20. State Chart for Vending Machine(Full behavior) Insert money (x) Push button Z [no drink Z]/ return money 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

21. Hierarchical State Chart Insert money (x) Coin slot has money Coin slot empty after (60 seconds)/return money Push button Z [sufficient money & drink Z in stock] Push button Z [no drink Z]/return money after (5 seconds) Dispensing Entry/ dispense drink, light up button, take money

22. 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

23. insertMoney(x) insertMoney(y) push() Sequence Diagram customer coinSlot button1 controller shelfRel1 shelfSens1 request(1) close() m:=checkAmount() getTotal() a:=checkAvailability() isEmpty() [!a] return() release() [m&a] lightUp() moveCoins() 5 sec open() lightDown()

24. insertMoney(x) insertMoney(x) insertMoney(y) insertMoney(y) push() Extension 2a customer coinSlot button1 controller timer set(60) set(60) 60 sec checkTime() checkTime() timeOut() return() set(60) set(60) < 60 sec request(1) close() reset()

25. Collaboration Diagram 2: push() button1 2.1: request(1) timer1 2.1.5 [m&a]: lightUp() 2a: timeOut() 2.1.1: close() 1.1: set(60) 3.2.2: lightDown() 2.1.2.1: getTotal() 2.1.1.1: reset() 2.1.4a [!a]: return() 2.1.4 [m&a]: release() 2.1.7 [m&a]: moveCoins() shelfRel 3.1.1: open() coinSlot controller 2.1.3.1: isEmpty() 1: insertMoney(x) «self» 2.1.2: m:=checkAmount() shelfSens 2.1.6: set(5) 2.1.3: a:=checkAvailability() 3: timeOut() timer2

26. Additional Design Technique: CRC Cards • CRC (class-responsibility-collaborator) 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

27. 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

28. Refined Class Diagram Timer set() reset() checkTime() Signals timeOut() CoinSlot amount: Integer opened: Bool insertMoney(Int) close() open() getTotal() return() moveCoins() 1 ShelfSens empty: Bool isEmpty() 3 1 1 1 Controller price: Integer request(Integer) checkAmount() checkAvailability() 1 1 Button id: Integer litUp: Bool push() lightUp() lightDown() 1 1 ShelfRel release() 3 3

29. 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

30. 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”

31. 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(); }

32. 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

33. 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

34. 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

35. 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