1. 8/7/2015CPSC-4360-01, CPSC-5360-01, Lecture 41 Software Engineering, CPSC-4360-01, CPSC-5360-01, Lecture 4

2. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 2 Review of Last Lecture Introduction to Case Studies Requirement Gathering Use Case Modeling Domain Modeling / Business Modeling Activity Diagram

3. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 3 Overview of This Lecture Analysis  Software Architecture  Use Case Realization Use Case → Sequence Diagrams  Domain Model Refinement Domain Model → Partial Class Diagram

4. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 4 Where are we now? Requirement Analysis Design Implement Test Analyze the system requirements. Use Case Realization:  Understanding how business entities can be used to support use cases.

5. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 5 Analysis: Overview Inputs:  Use Cases.  Domain Model. Activities:  Draft Software Architecture.  Realize Use Cases into Sequence Diagrams.  Refine Domain Model into Analysis Class Diagram.

6. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 6 Analysis: Overview The first bridging step from the external view (system behavior) to the internal view (system implementation). Requirements (Use Cases) give the external view. The Domain Model gives structural information about business entities. The Analysis is performed to understand how the business entities can be implemented and support use cases via Use Case Realization:  Adding operations to the business entities;  Move closer to an actual class in program.

7. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 7 Difference between Analysis & Design Distinction is not clear between the two activities:  Usually seen as one continuous activity with no clear boundary;  Made worse by using the same UML diagrams. Analysis:  Describes the structure of a real-world application;  Focus on requirements of system. Design:  Describes the structure of a proposed software system;  Focus on software structure that implements the system.

8. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 8 Difference between Analysis & Design While analysis model refers to identifying relevant objects in the real-world system, the design model is adding specific implementation details to the underlying analysis model. Famous phrase (page 7, [Larman, 2005]): “do the right thing (analysis), and do the thing right (design).” Example: Flight Information System [Larman, 2005]  Analysis: finding and describing the concepts/objects: Plane, Flight, Pilot, …  Design: defining software objects and how they collaborate to fulfill the requirements: a Plane object may have a tailNumber attribute and a getFlightHistory() method, …

9. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 9 What is Software Architecture? High level description of the overall system:  The top-level structure of subsystems.  The role and interaction of these subsystems. Grouping of classes to:  Improve Cohesion.  Reduce Coupling. Cohesion:  Set of “things” that work well together. Coupling:  Inter-Dependency between two entities.

10. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 10 Software Architecture: Example Take the minesweeper game as an example, and identify the high level components: Display:  Showing the game graphically. Application Logic:  Determining the flags, numbers.  Checking whether there are more mines, etc. Record Storage:  Storing high scores, setting, etc.

11. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 11 Minesweeper: System One class Minesweeper{ public void ClickOnSquare( ){ if (square == bomb) { gameState = dead show dead icon write high score to file } else if (square == number){ open neighboring squares mark squares as opened display new board } ………..// some other code } Bad Cohesion:  Display functions all over the place.  Application logic buried under other operations.  Storage function not clearly separated. Low Coupling:  Since there is only one class, there is no inter- dependency!

12. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 12 Minesweeper: System Two class MSGUI { Minesweeper msApp; MSStorage msStore; public void mouseClickOnSquare( ){ msApp.openSquare(..); board = msApp.getCurrentBoard(..); show(board); } public void menuExitClick( ) { score = msApp.getHighScore( ); msStore.writeHighScore(score); } class Minesweeper { MSStorage msStore; public void openSquare(position){ if (square == bomb) gameState = dead; else if (square == number){ open neighboring squares mark squares as opened; } public Board getCurrentBoard() {.. } public void saveCurrentBoard() { msStore.writeBoard(..); } class MSStorage { public void writeHighScore(..){ } public void writeBoard(..) { } }

13. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 13 Minesweeper: System Two Cohesion:  Each class groups logically similar functionality together: Class MSGUI : user interface, input/output to screen; Class Minesweeper : computation and logic; Class MSStorage : file operations. Coupling:  Some interdependencies. Can be improved.  Observe that MSGUI uses MSStorage directly.  Hence, if we substitute another user interface, the high score saving functionality needs to be recorded.

14. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 14 Minesweeper: System Three class MSGUI { Minesweeper msApp; // MSStorage msStore; Not needed...... public void menuExitClick( ) { msApp.closingDown( ); } class Minesweeper { MSStorage msStore;...... public void closingDown() { msStore.writeHighScore(..) } public void saveCurrentBoard() { } class MSStorage { public void writeHighScore(..){ } public void writeBoard(..){ } }

15. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 15 Minesweeper: System Three Coupling:  Reduced. MSGUI depends on Minesweeper only. Minesweeper depends on MSStorage only. Low coupling enables easy maintenance, e.g.:  Changing MSGUI to MSTextUI would not affect the main application at all.  Can swap in another storage class, e.g., database storage, by providing the same methods.

16. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 16 Minesweeper: Systems Comparison System 2 Minesweeper System 3 MSGui MSStorage Minesweeper MSGui MSStorage System 1 Minesweeper Bad Cohesion No Coupling Good Cohesion Medium Coupling Good Cohesion Low Coupling

17. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 17 Minesweeper: Observations Trade off between cohesion and coupling:  Improving cohesion usually implies worse (higher) coupling and vice versa. The three categories of functionality are quite widely applicable:  User Interface.  Main Application Logic.  Storage (Persistency). These observations help shaping Software Architecture:  splitting a system into sub-systems.

18. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 18 The Layered Architecture One of the oldest idea in Software Engineering. Split into three separate layers:  Presentation Layer User Interface.  Application Layer The underlying logic. Implements the functionality of system.  Storage Layer Deals with data storage: files, database, etc. The layers are higher level abstraction:  Each may contain several classes, or several packages (group of classes).

19. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 19 UML Package Diagram Dependency: Represent the “make use of” relationship. Package: Collection of classes or sub- packages.

20. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 20 Minesweeper: Package Diagram Presentation Minesweeper Application MSGUI MSStorage Storage Corresponds to programming construct:  Java: Package.  C++: namespace.

21. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 21 Layered Architecture: Advantages Layers aim to insulate a system from the effects of change. For example, user interfaces often change:  but the application layer does not use the presentation layer.  so changes to system should be restricted to presentation layer classes. Similarly, details of persistent data storage are separated from the application logic.

22. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 22 Analysis Class Stereotypes Within this architecture, objects can have various typical roles:  boundary objects: interact with outside actors.  control objects: manage use case behaviour.  entity objects: maintain data. These are represented explicitly in UML by using analysis class stereotypes. Give extra informal information for objects.

23. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 23 Stereotypes can be text or a graphic icon. The icon can replace the normal class box. Class Stereotype Notation

24. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 24 Use Case Realization: Overview Use case realization = implementation of the use case. Steps:  Go through each use case.  Identify interaction using a UML sequence diagram.  Refine the domain class diagram. Possible refinements:  Adding a new class and/or data.  Define association nagivability (direction) and role name.  Adding operation to an existing class. Focus is on System Functionality during Analysis phase.  Ignore other layers (Presentation and Storage).  Concentrate on the Application layer.

25. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 25 Sequence Diagram UML Diagram to:  Emphasize the interaction in the form of messages.  Identify the party involved in the interaction.  Outline the timing of the message.  Be mainly used in Analysis and Design activities. Analogy to help you understand:  In OO programs, objects interact with each others via method invocation (method call).  Method invocations can be modeled as messages passing between objects: ObjectA calls method M of ObjectB, is equivalent to ObjectA passes message M to ObjectB.  Sequence Diagram records these message passing.

26. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 26 Sequence Diagram Notation Simpler version of the sequence diagram used in design activity. Actor Class Entities Actors or Classes involve in interaction Lifeline Message With parameter Message ( Para ) Return Control and possibly value are returned Activation Bar Time Passes Returned value

27. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 27 Sequence Diagram: Explanation Time passes from top to bottom. Classes and actors at top:  only show those participating in this interaction.  each instance has a lifeline. Messages shown as arrows between lifelines:  labelled with operation name and parameters.  return messages (dashed) show return of control.  activations show when the receiver has control.

28. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 28 Sequence Diagram: Simple Example class A { public void example( ) { B objB; int result; //Sequence diagram shows the //following interaction result = objB.method(123); } } : B method ( 123 ) : A Returned 456

29. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 29 The initial realization consists of:  The Staff actor.  The System.  Message(s) passed between them. Case Study 1: Use Case Realization Display Bookings: Basic Course of Events  Staff enters a date;  System displays bookings for that date. Take Display Booking use case as example: Staff sends a message. System returns results.

30. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 30 Case Study 1: Use Case Realization The domain model shown in Lecture 3 does not contain a System class.  The Domain Model only concentrates on entities in the real world. A new class BookingSystem is added:  An example of domain model refinement.  Categorized as a control stereotype: Receives a high level request from the user. Contacts the relevant classes to fulfill the request.  Boundary stereotype is not appropriate: Emphasizes on the use case behavior, not input/output.

31. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 31 Case Study 1: Sequence Diagram The display(date) message originates from outside the system (it was called by an external user - Staff):  Termed as System Messages (opposite to Internal Messages, called from an object of the system). New class added System Message

32. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 32 System Sequence Diagram (SSD) Is a Sequence Diagram that shows only system messages:  An informal subtype of sequence diagram.  Concentrates on user-system exchange only.  Graphical representation of a use case.  Serves as a starting point for a more complete sequence diagram.

33. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 33 Case Study 1: Refining SSD ? How does the BookingSystem retrieves the bookings? Who should keep track of the bookings? Bad choices:  BookingSystem (why?)  Booking (why?)

34. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 34 Case Study 1: Refining SSD A class to store a collection of Bookings is needed. Adding this ability to BookingSystem is undesirable:  BookingSystem should only handle system messages.  Lower the cohesion of the class. Booking class in domain model:  Only records details of one booking. Not a collection. Hence, another new class is needed:  Restaurant class is a reasonable choice.  Can take care of other collections: Tables. Customers.

35. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 35 Case Study 1: Sequence Diagram Ver.1 New Class New Internal Message UI is not the focus at this stage. A placeholder function.

36. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 36 Case Study 1: Sequence Diagram Ver.1 The sequence diagram tells us:  Staff wants to check a booking for a particular date.  BookingSystem receives the request and asks the Restaurant to provides all bookings on that date. Follow up:  How can Restaurant find the relevant bookings from all bookings record?  One plausible way: Checks the date on each booking record, and collects only those that match.

37. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 37 Case Study 1: Sequence Diagram Ver.2 * denotes multiple messages The Booking class identified in the domain model

38. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 38 Case Study 1: Display Booking realization At this point, a plausible sequence of messages to achieve the use case has been identified. The sequence diagram can be used to refine the domain model. Several key refinements:  New Restaurant and BookingSystem classes with an association between them.  A new association from Restaurant to Booking. Restaurant maintains links to all bookings. Messages sent from restaurant to bookings.  Association from BookingSystem to Booking. BookingSystem maintains links to currently displayed bookings. If these were not stored once they had been displayed, then whenever the display was updated, the current bookings would have to be retrieved again from the Restaurant object.

39. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 39 Case Study 1: Updated Class Diagram (Partial) New class added Operation added New association added Association refined

40. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 40 Refining Association As we move closer to internal representation of the system, more technical information is needed for association. Two possible refinements:  Add navigability: The arrow above shows only A can interact with B, but not vice versa.  Add role name: A uses rName as the reference name of B. AB rName

41. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 41 Refining Association: Example The refined class diagram tells us:  Only Human is aware of the Mee, i.e., Human sends message to Mee, but not the other way around.  Human uses a reference myFood to refer to the instances of Mee, i.e.: HumanMee Eats > 1 Domain Model HumanMee myFood Eats > 1 Class Diagram class Human { Mee myFood; void method( ) { myFood.cook( ); } }

42. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 42 Case Study 1: Display Booking realization The Display Booking use case realization is complete at this point. Review:  Stop at System Sequence Diagram to make sure that every exchange between user and system is modeled.  From the SSD, figure out how entities in domain model can help to fulfill the request.  Add in the appropriate messages.  Refine domain model.

43. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 43 Case Study 1: Continuing Use Case Realization The basic technique has already been explained. Several Use Case realizations are chosen from Case Study 1 to highlight:  Additional notation for Sequence Diagram: Object Creation/Deletion. Role Name to distinguish objects of the same class.  Other possible refinement to domain model.

44. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 44 Case Study 1: Record Booking realization Restaurant is responsible for maintaining all bookings. makeReservation() should be handled by Restaurant.

45. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 45 Case Study 1: Record Booking realization Bookings must be linked to Table and Customer:  Restaurant retrieves these with the given identifying data in booking details. New objects shown at point of creation:  Lifeline starts from that point.  Objects created by a message arriving at the instance, i.e., constructor.

46. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 46 Case Study 1: Creating New Booking Object New Object Constructor Message

47. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 47 Case Study 1: Cancel Booking realization A three-stage process:  Select the booking to be cancelled.  Confirm cancellation with user.  Delete the corresponding booking object. Object deletion represented by a message with a > stereotype.  Lifeline terminates with an ‘X’. Role names used to distinguish the selected object from others.

48. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 48 Case Study 1: Cancel Booking Sequence Diagram Destruction message Lifeline Terminated Role Name

49. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 49 Case Study 1: Domain Model Refinement Continues BookingSystem has the responsibility to remember which booking is selected. Adds an association to record this. Association Added

50. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 50 Case Study 1: Record Arrival Realization

51. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 51 Case Study 1: Record Arrival Realization Selected Booking must be a Reservation.

52. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 52 Case Study 1: Refining Class Diagram Should setArrivalTime( ) be defined in Booking or in Reservation class?  On the one hand, it doesn't apply to Walk-Ins.  But a common interface to all bookings is desirable. Define operation in Booking class.  Default implementation does nothing.  Override in Reservation class.

53. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 53 Case Study 1: Refining Class Hierarchy Common interface for all subclasses Override in subclass

54. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 54 Case Study1: Complete Analysis Class Model

55. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 55 Where are we now? Requirement Analysis Design Implement Test Typical Artifacts:  Software Architecture  Sequence Diagrams  Analysis Class Diagram

56. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 56 Summary Analysis has led to:  A set of use case realizations.  A refined class diagram. We can see how the class design is going to support the functionality of the use cases. This gives confidence that the overall design will work.

57. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 57 Reading Suggestions Chapter 4 of [Bimlesh, Andrei, Soo; 2007] Chapter 5 of [Priestley; 2004]

58. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 58 Coming up next Object-oriented design – Chapter 5 of [Bimlesh, Andrei, Soo; 2007] Design - Chapter 6 of [Priestley; 2004] UML Class and Object Diagrams - Chapter 8 [Priestley; 2004]

59. 8/7/2015 CPSC-4360-01, CPSC-5360-01, Lecture 4 59 Thank you for your attention! Questions?