1. Conquering Complex and Changing Systems Object-Oriented Software Engineering Chapter 5, Analysis: Dynamic Modeling

2. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 2 Outline  Dynamic modeling  Sequence diagrams  State diagrams  Using dynamic modeling for the design of user interfaces  Analysis example  Requirements analysis document template

3. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 3 Example of use case format Use case name ReportEmergency Entry condition 1. The FieldOfficer activates the “Report Emergency” function of her terminal. Flow of events 2. FRIEND responds by presenting a form to the officer... 3. The FieldOfficer fills the form.... 4. The Dispatcher reviews the information submitted by the FieldOfficer... Exit condition 5. The FieldOfficer receives the acknowledgment and the selected response.

4. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 4 How do you find classes?  From previous lectures  Application domain analysis: Talk to client to identify abstractions  Apply general world knowledge and intuition  Scenarios  Natural language formulation of a concrete usage of the system  Use Cases  Natural language formulation of the functions of the system  Textual analysis of problem statement (Abbot)  From this lecture  Dynamic model  Events: Candiates for operations to be offered by classes  Sequence diagrams as sources for objects  From future lectures  Design Patterns

5. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 5 Dynamic Modeling with UML  Diagrams for dynamic modeling  Interaction diagrams describe the dynamic behavior between objects  Statecharts describe the dynamic behavior of a single object  Interaction diagrams  Sequence Diagram:  Dynamic behavior of a set of objects arranged in time sequence.  Good for real-time specifications and complex scenarios  Collaboration Diagram :  Shows the relationship among objects. Does not show time  State Charts:  A state machine that describes the response of an object of a given class to the receipt of outside stimuli (Events).  Activity Diagram:  Special type of statechart where all states are action states

6. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 6 Dynamic Modeling  Definition of dynamic model:  A collection of multiple state chart diagrams, one state chart diagram for each class with important dynamic behavior.  Purpose:  Detect and supply methods for the object model  How do we do this?  Start with use case or scenario  Model interaction between objects => sequence diagram  Model dynamic behavior of single objects => statechart diagram

7. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 7 Start with Flow of Events from Use Case  Flow of events from “Dial a Number” Use case:  Caller lifts receiver  Dail tone begins  Caller dials  Phone rings  Callee answers phone  Ringing stops ....

8. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 8 What is an Event?  Something that happens at a point in time  Relation of events to each other:  Causally related: Before, after,  Causally unrelated: concurrent  An event sends information from one object to another  Events can be grouped in event classes with a hierarchical structure. ‘Event’ is often used in two ways:  Instance of an event class: “New IETM issued on Thursday September 14 at 9:30 AM”.  Event class “New IETM”, Subclass “Figure Change”  Attribute of an event class  IETM Update (9:30 AM, 9/14/99)  Car starts at ( 4:45pm, Monroeville Mall, Parking Lot 23a)  Mouse button down(button#, tablet-location)

9. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 9 Sequence Diagram  From the flow of events in the use case or scenario proceed to the sequence diagram  A sequence diagram is a graphical description of objects participating in a use case or scenario using a DAG notation  Relation to object identification:  Objects/classes have already been identified during object modeling  Objects are identified as a result of dynamic modeling  Heuristic:  An event always has a sender and a receiver. Find them for each event => These are the objects participating in the use case

10. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 10 An Example  Flow of events in a “Get SeatPosition” use case : 1. Establish connection between smart card and onboard computer 2. Establish connection between onboard computer and sensor for seat 3. Get current seat position and store on smart card  Which are the objects?

11. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 11 Sequence Diagram for “Get SeatPosition” Smart Card Onboard Computer Seat Establish Connection Accept Connection Get SeatPosition “500,575,300” 1. Establish connection between smart card and onboard computer 2. Establish connection between onboard computer and sensor for seat 3. Get current seat position and store on smart card

12. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 12 Heuristics for Sequence Diagrams  Layout:  1st column: Should correspond to the actor who initiated the use case  2nd column: Should be a boundary object  3rd column: Should be the control object that manages the rest of the use case  Creation:  Control objects are created at the initiation of a use case  Boundary objects are created by control objects  Access:  Entity objects are accessed by control and boundary objects,  Entity objects should never call boundary or control objects: This makes it easier to share entity objects across use cases and makes entity objects resilient against technology-induced changes in boundary objects.

13. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 13 Is this a good Sequence Diagram? Smart Card Onboard Computer Seat Establish Connection Accept Connection Get SeatPosition “500,575,300” Did the modeler follow the heuristics?

14. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 14 UML Statechart Diagram Notation State2 State1 Event1(attr) [condition]/action entry /action exit/action  Notation based on work by Harel  Added are a few object-oriented modifications  A UML statechart diagram can be mapped into a finite state machine do/Activity Also: internal transition and deferred events Event trigger With parameters Guard condition

15. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 15 Statechart Diagrams  Graph whose nodes are states and whose directed arcs are transitions labeled by event names.  Distinguish between two types of operations:  Activity: Operation that takes time to complete  associated with states  Action: Instantaneous operation  associated with events  associated with states (reduces drawing complexity): Entry, Exit, Internal Action  A statechart diagram relates events and states for one class  An object model with a set of objects has a set of state diagrams

16. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 16 State  An abstraction of the attribute of a class  State is the aggregation of several attributes a class  Basically an equivalence class of all those attribute values and links that do no need to be distinguished as far as the control structure of the system is concerned  Example: State of a bank  A bank is either solvent or insolvent  State has duration

17. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 17 Example of a StateChart Diagram Idle Collect Money coins_in(amount) / add to balance do: test item and compute change do: make change do: dispense item [change=0] [change>0] [item empty] [select(item)] [change<0] coins_in(amount) / set balance cancel / refund coins

18. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 18 Nested State Diagram  Activities in states are composite items denoting other lower- level state diagrams  A lower-level state diagram corresponds to a sequency of lower-level states and events that are invisible in the higher- level diagram.  Sets of substates in a nested state diagram denoting a superstate are enclosed by a large rounded box, also called contour.

19. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 19 Example of a Nested Statechart Diagram Superstate Idle Collect Money coins_in(amount) / add to balance do: test item and compute change do: make change do: dispense item [change=0] [change>0] [item empty] [select(item)] [change<0] coins_in(amount) / set balance cancel / refund coins

20. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 20 Expanding activity “do:dispense item” do: move arm to row do: move arm to column do: push item off shelf Arm ready ‘Dispense item’ as an atomic activity: ‘Dispense item’ as a composite activity: do: dispense item [change=0] Arm ready

21. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 21 Superstates  Goal:  Avoid spaghetti models  Reduce the number of lines in a state diagram  Transitions from other states to the superstate enter the first substate of the superstate.  Transitions to other states from a superstate are inherited by all the substates (state inheritance)

22. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 22 Modeling Concurrency Two types of concurrency 1. System concurrency  State of overall system as the aggregation of state diagrams, one for each object. Each state diagram is executing concurrently with the others. 2. Object concurrency  An object can be partitioned into subsets of states (attributes and links) such that each of them has its own subdiagram.  The state of the object consists of a set of states: one state from each subdiagram.  State diagrams are divided into subdiagrams by dotted lines.

23. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 23 Example of Concurrency within an Object Emitting Setting Ready Up to reset Do: Dispense Cash Do: Eject Card Ready Cash taken Card taken Synchronization Splitting control

24. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 24 State Chart Diagram vs Sequence Diagram  State chart diagrams help to identify:  Changes to objects over time  Sequence diagrams help to identify  The temporal relationship of between objects over time  Sequence of operations as a response to one ore more events

25. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 25 Dynamic Modeling of User Interfaces  Statechart diagrams can be used for the design of user interfaces  Also called Navigation Path  States: Name of screens  Graphical layout of the screens associated with the states helps when presenting the dynamic model of a user interface  Activities/actions are shown as bullets under screen name  Often only the exit action is shown  State transitions: Result of exit action  Button click  Menu selection  Cursor movements  Good for web-based user interface design

26. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 26 Navigation Path Example (15-499 Spring 96) Diagnostics User can move cursor to Control Panel or Graph Graph User can select data group and type of graph Selection User selects data group Field site Car Sensor group Time range User selects type of graph time line histogram pie chart Visualize User views graph User can add data groups for being viewed Link User makes a link (doclink) Control panel User can select functionality of sensors Disable User can disable a sensor event from a list of sensor events Define User defines a sensor event from a list of events Enable User can enable a sensor event from a list of sensor events List of sensor events User selects sensor event(s) List of events User selects event(s)

27. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 27 Practical Tips for Dynamic Modeling  Construct dynamic models only for classes with significant dynamic behavior  Avoid “analysis paralysis”  Consider only relevant attributes  Use abstraction if necessary  Look at the granularity of the application when deciding on actions and activities  Reduce notational clutter  Try to put actions into state boxes (look for identical actions on events leading to the same state)

28. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 28 Summary: Requirements Analysis  1. What are the transformations?  Create scenarios and use case diagrams  Talk to client, observe, get historical records, do thought experiments  2. What is the structure of the system?  Create class diagrams  Identify objects. What are the associations between them? What is their multiplicity?  What are the attributes of the objects?  What operations are defined on the objects?  3. What is its control structure?  Create sequence diagrams  Identify senders and receivers  Show sequence of events exchanged between objects. Identify event dependencies and event concurrency.  Create state diagrams  Only for the dynamically interesting objects. Dynamic Modeling Functional Modeling Object Modeling

29. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 29 Let’s Do Analysis 1. Analyze the problem statement  Identify functional requirements  Identify nonfunctional requirements  Identify constraints (pseudo requirements) 2. Build the functional model:  Develop use cases to illustrate functionality requirements 3. Build the dynamic model:  Develop sequence diagrams to illustrate the interaction between objects  Develop state diagrams for objects with interesting behavior 4. Build the object model:  Develop class diagrams showing the structure of the system

30. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 30 Problem Statement: Direction Control for a Toy Car  Power is turned on  Car moves forward and car headlight shines  Power is turned off  Car stops and headlight goes out.  Power is turned on  Headlight shines  Power is turned off  Headlight goes out.  Power is turned on  Car runs backward with its headlight shining.  Power is turned on  Car moves forward and car headlight shines  Power is turned off  Car stops and headlight goes out.  Power is turned on  Headlight shines  Power is turned off  Headlight goes out.  Power is turned on  Car runs backward with its headlight shining.  Power is turned off  Car stops and headlight goes out.  Power is turned on  Headlight shines  Power is turned off  Headlight goes out.  Power is turned on  Car runs forward with its headlight shining.  Power is turned off  Car stops and headlight goes out.  Power is turned on  Headlight shines  Power is turned off  Headlight goes out.  Power is turned on  Car runs forward with its headlight shining.

31. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 31 Find the Functional Model: Do Use Case Modeling  Use case 1: System Initialization  Entry condition: Power is off, car is not moving  Flow of events:  Driver turns power on  Exit condition: Car moves forward, headlight is on  Use case 2: Turn headlight off  Entry condition: Car moves forward with headlights on  Flow of events:  Driver turns power off, car stops and headlight goes out.  Driver turns power on, headlight shines and car does not move.  Driver turns power off, headlight goes out  Exit condition: Car does not move, headlight is out

32. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 32 Use Cases continued  Use case 3: Move car backward  Entry condition: Car is stationary, headlights off  Flow of events:  Driver turns power on  Exit condition: Car moves backward, headlight on  Use case 4: Stop backward moving car  Entry condition: Car moves backward, headlights on  Flow of events:  Driver turns power off, car stops, headlight goes out.  Power is turned on, headlight shines and car does not move.  Power is turned off, headlight goes out.  Exit condition: Car does not move, headlight is out.  Use case 5: Move car forward  Entry condition: Car does not move, headlight is out  Flow of events  Driver turns power on  Exit condition:  Car runs forward with its headlight shining.

33. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 33 Use Case Pruning  Do we need use case 5?  Use case 1: System Initialization  Entry condition: Power is off, car is not moving  Flow of events:  Driver turns power on  Exit condition: Car moves forward, headlight is on  Use case 5: Move car forward  Entry condition: Car does not move, headlight is out  Flow of events  Driver turns power on  Exit condition:  Car runs forward with its headlight shining.

34. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 34 Find the Dynamic Model: Create sequence diagram  Name: Drive Car  Sequence of events:  Billy turns power on  Headlight goes on  Wheels starts moving forward  Wheels keeps moving forward  Billy turns power off  Headlight goes off  Wheels stops moving ...

35. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 35 Sequence Diagram for Drive Car Scenario Power(on) :HeadlightBilly:Driver :Wheel Power(off) Power(on) Power(off) Power(on)

36. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 36 Toy Car: Dynamic Model Wheel Forward Backward Stationary power on power off power off power on Headlight power on power off Off On

37. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 37 Toy Car: Object Model Wheel Motion: (Forward, Stationary) Backward, Start_Moving() Stop_Moving() Headlight Status: (On, Off) Switch_On() Switch_Off() Power Status: (On, Off) TurnOn() TurnOff() Car

38. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 38 When is a model dominant?  Object model: The system has non-trivial data structures.  Dynamic model: The model has many different types of events: Input, output, exceptions, errors, etc.  Functional model: The model performs complicated transformations such as difficult computations consisting of many steps.  Examples:  Compiler: Functional model most important. Dynamic model is trivial because there is only one type input and only a few outputs.  Database systems: Object model most important. Functional model is trivial, because their purpose is usually only to store, organize and retrieve data.  Spreadsheet program: Functional model most important. Object model is trivial, because the spreadsheet values are trivial and cannot be structured further. The only interesting object is the cell.

39. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 39 Collaborative Analysis  A system is a collection of subsystems providing services  Analysis of services is provided by a set of the teams who provide the models for their subsystems  Integration of subsystem models into the full system model by the architecture team  Analysis integration checklist:  Are all the classes mentioned in the data dictionary?  Are the names of the methods consistent with the names of actions, activities, events or processes?  Check for assumptions made by each of the services  Missing methods, classes  Unmatched associations

40. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 40 Analysis: UML Activity Diagram

41. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 41 Object Model Integration in JAMES (Fall 1997) Module 1 Team 1 User Interface Team User Interface Module Integration Integrated System Model Revised System Model Module 5 Module 4 Team 5 Team 4 Module 3 Team 3 Module 2 Team 2 Analysis Review Analysis All Teams Model Changes Architecture Team

42. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 42 Consistency, Completeness, Ambiguities  Consistency  Identification of crossed “wires” between classes  Naming of classes, attributes, methods  Completeness:  Identification of dangling associations (associations pointing to nowhere)  Identification of double- defined classes  Identification of missing classes (referred to by one subsystem but not defined anywhere)  Ambiguities  Misspelling of names  Classes with the same name but different meanings

43. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 43 Requirements Analysis Document Template 1.Introduction 2.Current system 3.Proposed system 3.1Overview 3.2Functional requirements 3.3Nonfunctional requirements 3.4Constraints (“Pseudo requirements”) 3.5System models 3.5.1 Scenarios 3.5.2 Use case model 3.5.3 Object model 3.5.3.1 Data dictionary 3.5.3.2 Class diagrams 3.5.4 Dynamic models 3.5.5 User interfae 4. Glossary

44. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 44 Section 3.5 System Model 3.5.1 Scenarios - As-is scenarios, visionary scenarios 3.5.2 Use case model - Actors and use cases 3.5.3 Object model - Data dictionary - Class diagrams (classes, associations, attributes and operations) 3.5.4 Dynamic model - State diagrams for classes with significant dynamic behavior - Sequence diagrams for collaborating objects (protocol) 3.5.5 User Interface - Navigational Paths, Screen mockups

45. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 45 Section 3.3 Nonfunctional Requirements 3.3.1 User interface and human factors 3.3.2 Documentation 3.3.3 Hardware considerations 3.3.4 Performance characteristics 3.3.5 Error handling and extreme conditions 3.3.6 System interfacing 3.3.7 Quality issues 3.3.8 System modifications 3.3.9 Physical environment 3.3.10 Security issues 3.3.11 Resources and management issues

46. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 46 Nonfunctional Requirements: Trigger Questions 3.3.1 User interface and human factors  What type of user will be using the system?  Will more than one type of user be using the system?  What sort of training will be required for each type of user?  Is it particularly important that the system be easy to learn?  Is it particularly important that users be protected from making errors?  What sort of input/output devices for the human interface are available, and what are their characteristics? 3.3.2 Documentation  What kind of documentation is required?  What audience is to be addressed by each document? 3.3.3 Hardware considerations  What hardware is the proposed system to be used on?  What are the characteristics of the target hardware, including memory size and auxiliary storage space?

47. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 47 Nonfunctional Requirements (continued) 3.3.4 Performance characteristics  Are there any speed, throughput, or response time constraints on the system?  Are there size or capacity constraints on the data to be processed by the system? 3.3.5 Error handling and extreme conditions  How should the system respond to input errors?  How should the system respond to extreme conditions? 3.3.6 System interfacing  Is input coming from systems outside the proposed system?  Is output going to systems outside the proposed system?  Are there restrictions on the format or medium that must be used for input or output?

48. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 48 Nonfunctional Requirements, ctd  3.3.7 Quality issues  What are the requirements for reliability?  Must the system trap faults?  Is there a maximum acceptable time for restarting the system after a failure?  What is the acceptable system downtime per 24-hour period?  Is it important that the system be portable (able to move to different hardware or operating system environments)?  3.3.8 System Modifications  What parts of the system are likely candidates for later modification?  What sorts of modifications are expected?  3.3.9 Physical Environment  Where will the target equipment operate?  Will the target equipment be in one or several locations?  Will the environmental conditions in any way be out of the ordinary (for example, unusual temperatures, vibrations, magnetic fields,...)?

49. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 49 Nonfunctional Requirements, ctd  3.3.10 Security Issues  Must access to any data or the system itself be controlled?  Is physical security an issue?  3.3.11 Resources and Management Issues  How often will the system be backed up?  Who will be responsible for the back up?  Who is responsible for system installation?  Who will be responsible for system maintenance?

50. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 50 Pseudo Requirements (Constraints)  Pseudo requirement:  Any client restriction on the solution domain  Examples:  The target platform must be an IBM/360  The implementation language must be COBOL  The documentation standard X must be used  A dataglove must be used  ActiveX must be used  The system must interface to a papertape reader

51. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 51 Project Agreement  The project agreement represents the acceptance of the analysis model (as documented by the requirements analysis document) by the client.  The client and the developers converge on a single idea and agree about the functions and features that the system will have. In addition, they agree on:  a list of priorities  a revision process  a list of criteria that will be used to accept or reject the system  a schedule, and a budget

52. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 52 Prioritizing requirements  High priority (“Core requirements”)  Must be addressed during analysis, design, and implementation.  A high-priority feature must be demonstrated successfully during client acceptance.  Medium priority (“Optional requirements”)  Must be addressed during analysis and design.  Usually implemented and demonstrated in the second iteration of the system development.  Low priority (“Fancy requirements”)  Must be addressed during analysis (“very visionary scenarios”).  Illustrates how the system is going to be used in the future if not yet available technology enablers are

53. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 53 Summary In this lecture, we reviewed the construction of the dynamic model from use case and object models. In particular, we described: In particular, we described:  Sequence diagrams for identifying missing objects and operations.  Statechart diagrams for identifying missing attributes.  Definition of an event hierarchy. In addition, we described the requirements analysis document and its use when interacting with the client.

54. Conquering Complex and Changing Systems Object-Oriented Software Engineering Chapter 6, System Design Lecture 1

55. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 55 Design “There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies.” - C.A.R. Hoare

56. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 56 Why is Design so Difficult?  Analysis: Focuses on the application domain  Design: Focuses on the implementation domain  Design knowledge is a moving target  The reasons for design decisions are changing very rapidly  Halftime knowledge in software engineering: About 3-5 years  What I teach today will be out of date in 3 years  Cost of hardware rapidly sinking  “Design window”:  Time in which design decisions have to be made

57. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 57 The Purpose of System Design  Bridging the gap between desired and existing system in a manageable way  Use Divide and Conquer  We model the new system to be developed as a set of subsystems Problem Existing System New System

58. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 58 System Design 2. System Layers/Partitions Coherence/Coupling 5. Data 1. Design Goals Definition Trade-offs 4. Hardware/ Special purpose Software Buy or Build Trade-off Allocation Connectivity 3. Concurrency Data structure Persistent Objects Files Databases Management Access control Security 6. Global Resource Handling 8. Boundary Conditions Initialization Termination Failure Decomposition Mapping 7. Software Control Identification of Threads Monolithic Event-Driven Threads Conc. Processes

59. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 59 Overview System Design I 0. Overview of System Design 1. Design Goals 2. Subsystem Decomposition System Design II (next lecture) 3. Concurrency 4. Hardware/Software Mapping 5. Persistent Data Management 6. Global Resource Handling and Access Control 7. Software Control 8. Boundary Conditions

60. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 60 How to use the results from the Requirements Analysis for System Design  Nonfunctional requirements =>  Activity 1: Design Goals Definition  Use Case model =>  Activity 2: System decomposition (Selection of subsystems based on functional requirements, coherence, and coupling)  Object model =>  Activity 4: Hardware/software mapping  Activity 5: Persistent data management  Dynamic model =>  Activity 3: Concurrency  Activity 6: Global resource handling  Activity 7: Software control  Activity 8: Boundary conditions

61. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 61 Section 1. Design Goals  Reliability  Modifiability  Maintainability  Understandability  Adaptability  Reusability  Efficiency  Portability  Traceability of requirements  Fault tolerance  Backward-compatibility  Cost-effectiveness  Robustness  High-performance  Good documentation  Well-defined interfaces  User-friendliness  Reuse of components  Rapid development  Minimum # of errors  Readability  Ease of learning  Ease of remembering  Ease of use  Increased productivity  Low-cost  Flexibility

62. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 62 Relationship Between Design Goals Reliability Low cost Increased Productivity Backward-Compatibility Traceability of requirements Rapid development Flexibility Client End User (Customer, Portability Good Documentation Runtime Efficiency Sponsor) Developer/ Maintainer Minimum # of errors Modifiability, Readability Reusability, Adaptability Well-defined interfaces Functionality User-friendliness Ease of Use Ease of learning Fault tolerant Robustness

63. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 63 Typical Design Trade-offs  Functionality vs. Usability  Cost vs. Robustness  Efficiency vs. Portability  Rapid development vs. Functionality  Cost vs. Reusability  Backward Compatibility vs. Readability

64. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 64 Nonfunctional Requirements give a clue for the use of Design Patterns  Read the problem statement again  Use textual clues (similar to Abbot’s technique in Analysis) to identify design patterns  Text: “manufacturer independent”, “device independent”, “must support a family of products”  Abstract Factory Pattern  Text: “must interface with an existing object”  Adapter Pattern  Text: “must deal with the interface to several systems, some of them to be developed in the future”, “ an early prototype must be demonstrated”  Bridge Pattern

65. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 65 Textual Clues in Nonfunctional Requirements  Text: “complex structure”, “must have variable depth and width”  Composite Pattern  Text: “must interface to an set of existing objects”  Façade Pattern  Text: “must be location transparent”  Proxy Pattern  Text: “must be extensible”, “must be scalable”  Observer Pattern  Text: “must provide a policy independent from the mechanism”  Strategy Pattern

66. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 66 Section 2. System Decomposition  Subsystem (UML: Package)  Collection of classes, associations, operations, events and constraints that are interrelated  Seed for subsystems: UML Objects and Classes.  Service:  Group of operations provided by the subsystem  Seed for services: Subsystem use cases  Service is specified by Subsystem interface:  Specifies interaction and information flow from/to subsystem boundaries, but not inside the subsystem.  Should be well-defined and small.  Often called API: Application programmer’s interface, but this term should used during implementation, not during System Design

67. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 67 Services and Subsystem Interfaces  Service: A set of related operations that share a common purpose  Notification subsystem service:  LookupChannel()  SubscribeToChannel()  SendNotice()  UnscubscribeFromChannel()  Services are defined in System Design  Subsystem Interface: Set of fully typed related operations. Also called application programmer interface (API)  Subsystem Interfaces are defined in Object Design

68. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 68 Choosing Subsystems  Criteria for subsystem selection: Most of the interaction should be within subsystems, rather than across subsystem boundaries (High coherence).  Does one subsystem always call the other for the service?  Which of the subsystems call each other for service?  Primary Question:  What kind of service is provided by the subsystems (subsystem interface)?  Secondary Question:  Can the subsystems be hierarchically ordered (layers)?  What kind of model is good for describing layers and partitions?

69. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 69 Example: STARS Subsystem Decomposition Is this the right decomposition or is this too much ravioli? ModelingAuthoringWorkorderRepairInspection Augmented Reality Workflow

70. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 70 Definition: Subsystem Interface Object  A Subsystem Interface Object provides a service  This is the set of public methods provided by the subsystem  The Subsystem interface describes all the methods of the subsystem interface object  Use a Facade pattern for the subsystem interface object

71. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 71 STARS as a set of subsystems communicating via a software bus Authoring Modeling Augmented Reality Workorder Repair Inspection Workflow A Subsystem Interface Object publishes the service (= Set of public methods) provided by the subsystem

72. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 72 STARS as a 3-layered Architecture What is the relationship between Modeling and Authoring? Are other subsystems needed? RepairInspectionAuthoring Augmented Reality WorkflowModeling

73. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 73 Coupling and Coherence  Goal: Reduction of complexity  Coherence measures the dependence among classes  High coherence: The classes in the subsystem perform similar tasks and are related to each other (via associations)  Low coherence: Lots of misc and aux objects, no associations  Coupling measures dependencies between subsystems  High coupling: Modifications to one subsystem will have high impact on the other subsystem (change of model, massive recompilation, etc.)  Subsystems should have as maximum coherence and minimum coupling as possible:  How can we achieve loose coupling?  Which subsystems are highly coupled?

74. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 74 Partitions and Layers A large system is usually decomposed into subsystems using both, layers and partitions.  Partitions vertically divide a system into several independent (or weakly-coupled) subsystems that provide services on the same level of abstraction.  A layer is a subsystem that provides services to a higher level of abstraction  A layer can only depend on lower layers  A layer has no knowledge of higher layers

75. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 75 Layer 1 Layer 2 Layer 3 Subsystem Decomposition into Layers  Subsystem Decomposition Heuristics:  No more than 7+/-2 subsystems  More subsystems increase coherence but also complexity (more services)  No more than 5+/-2 layers

76. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 76 Layer and Partition Relationships between Subsystems  Layer relationship  Layer A “Calls” Layer B (runtime)  Layer A “Depends on” Layer B (“make” dependency, compile time)  Partition relationship  The subsystem have mutual but not deep knowledge about each other  Partition A “Calls” partition B and partition B “Calls” partition A

77. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 77 Virtual Machine (Dijkstra, 1965)  A system should be developed by an ordered set of virtual machines, each built in terms of the ones below it. VM4 VM3 VM2 VM1 C1 attr opr C1 attr opr C1 attr opr C1 attr opr C1 attr opr C1 attr opr C1 attr opr C1 attr opr Problem Existing System

78. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 78 Virtual Machine  A virtual machine is an abstraction that provides a set of attributes and operations.  A virtual machine is a subsystem connected to higher and lower level virtual machines by "provides services for" associations.  Virtual machines can implement two types of software architecture: closed and open architectures.

79. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 79 Closed Architecture (Opaque Layering)  A virtual machine can only call operations from the layer below  Design goal: High maintainability VM4 VM3 VM2 VM1 C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op

80. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 80 Open Architecture (Transparent Layering)  A virtual machine can call operations from any layers below  Design goal: Runtime efficiency VM4 VM3 VM2 VM1 C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op C1 attr op

81. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 81 Properties of Layered Systems  Layered systems are hierarchical. They are desirable because hierarchy reduces complexity.  Closed architectures are more portable.  Open architectures are more efficient.  If a subsystem is a layer, it is often called a virtual machine.  Layered systems often have a chicken-and egg problem  Example: Debugger opening the symbol table when the file system needs to be debugged

82. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 82 Software Architectures  Subsystem decomposition  Identification of subsystems, services, and their relationship to each other.  Specification of the system decomposition is critical.  Patterns for software architecture  Client/Server Architecture  Peer-To-Peer Architecture  Repository Architecture  Model/View/Controller  Pipes and Filters Architecture

83. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 83 Client/Server Architecture  One or many servers provides services to instances of subsystems, called clients.  Client calls on the server, which performs some service and returns the result  Client knows the interface of the server (its service)  Server does not need to know the interface of the client  Response in general immediately  Users interact only with the client

84. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 84 Client/Server Architecture  Often used in database systems:  Front-end: User application (client)  Back end: Database access and manipulation (server)  Functions performed by client:  Customized user interface  Front-end processing of data  Initiation of server remote procedure calls  Access to database server across the network  Functions performed by the database server:  Centralized data management  Data integrity and database consistency  Database security  Concurrent operations (multiple user access)  Centralized processing (for example archiving)

85. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 85 Design Goals for Client/Server Systems  Portability  Server can be installed on a variety of machines and operating systems and functions in a variety of networking environments  Transparency  The server might itself be distributed (why?), but should provide a single "logical" service to the user  Performance  Client should be customized for interactive display-intensive tasks  Server should provide CPU-intensive operations  Scalability  Server has spare capacity to handle larger number of clients  Flexibility  Should be usable for a variety of user interfaces  Reliability  System should survive individual node and/or communication link problems

86. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 86 Problems with Client/Server Architectures  Layered systems do not provide peer-to-peer communication  Peer-to-peer communication is often needed  Example: Database receives queries from application but also sends notifications to application when data have changed

87. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 87 Peer-to-Peer Architecture  Generalization of Client/Server Architecture  Clients can be servers and servers can be clients  More difficult because of possibility of deadlocks

88. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 88 Application Presentation Session Transport Network DataLink Physical Frame Packet Bit Connection Format Message Level of abstraction Example of a Peer-to-Peer Architecture  ISO’s OSI Reference Model  ISO = International Standard Organization  OSI = Open System Interconnection  Reference model defines 7 layers of network protocols and strict methods of communication between the layers.

89. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 89 Middleware Allows You To Focus On The Application Layer Application Presentation Session Transport Network DataLink Physical Socket CORBA TCP/IP Object Ethernet Wire

90. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 90 Model/View/Controller  Subsystems are classified into 3 different types  Model subsystem: Responsible for application domain knowledge  View subsystem: Responsible for displaying application domain objects to the user  Controller subsystem: Responsible for sequence of interactions with the user and notifying views of changes in the model.  MVC is a special case of a repository architecture:  Model subsystem implements the central datastructure, the Controller subsystem explicitly dictate the control flow Controller Model subscriber notifier initiator * repository1 1 * View

91. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 91 Example of a File System based on MVC Architecture

92. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 92 Sequence of Events :Controller :InfoView :Model 2.User types new filename 1. Views subscribe to event 3. Request name change in model 4. Notify subscribers 5. Updated views :FolderView

93. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 93 Repository Architecture  Subsystems access and modify data from a single data structure  Subsystems are loosely coupled (interact only through the repository)  Control flow is dictated by central repository (triggers) or by the subsystems (locks, synchronization primitives) Subsystem Repository createData() setData() getData() searchData()

94. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 94 Examples of Repository Architecture  Hearsay II speech understanding system (“Blackboard architecture”)  Database Management Systems  Modern Compilers LexicalAnalyzer SyntacticAnalyzer SemanticAnalyzer CodeGenerator Compiler SyntacticEditor ParseTree SymbolTable Repository SourceLevelDebugger Optimizer

95. UNB CS3013 Software Engineering II lectures adapted from Bernd Bruegge & Allen Dutoit, Object-Oriented Software Engineering: Conquering Complex and Changing Systems 95 Summary  System Design  Reduces the gap between requirements and the machine  Decomposes the overall system into manageable parts  Design Goals Definition  Describes and prioritizes the qualities that are important for the system  Defines the value system against which options are evaluated  Subsystem Decomposition  Results into a set of loosely dependent parts which make up the system