Workshop on Basics of Software Engineering (DFD, UML and Project Culture)


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Three days workshop on Basics of Software Engineering at Thapar University, Patiala on 7th-9th, 2013. Workshop on Basics of Software Engineering (DFD, UML and Project Culture)

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Workshop on Basics of Software Engineering (DFD, UML and Project Culture)

  1. 1. 1
  2. 2. Module 1 Introduction Module 2 Use case diagram Module 3 Flow of events Module 4 Realization of the class diagram Module 5 Sequence diagram and Collaboration Diagram Module 6 Class diagram and refinement attributes Module 7 State transition and activity diagram Module 8 Implementation diagram Module 9 Component diagram and Deployment diagram Module 10 Understanding project culture 2
  3. 3. 3
  4. 4.  What is a model? ◦ A model is a simplification of reality  Why do we model? ◦ help visualizing ◦ permit specification ◦ provides a template ◦ document decisions 4
  5. 5.  Choose your models well  Every model may be expressed at various levels of precision  The best models are connected to reality  No single model is sufficient 5
  6. 6.  DEFINITION:The application of systematic, disciplined and qualifiable approach to the development, operation and maintenance of a software system is software engineering.  Software development life cycle has following stages: 6 REQUIREMENT ANALYSIS DESIGN IMPLEMENTATION TESTING
  7. 7. Analysis & design 40 % Development 20 % Testing 40 % Analysis - What is to be done ? Design - How it is to be done ? Two Popular methodology approaches are:  Structured Analysis & Design  Object Oriented Analysis & Design-OO model 7
  8. 8. The object oriented approach is a way of thinking about a problem using real world concepts instead using adhoc function concepts. We intent to learn OOAD approach for the following reason: ◦Promotes better understanding of user requirements ◦Leads cleaner design ◦Design flexibility' ◦Decomposition of the system is consistent ◦Facilitates data abstraction & information hiding ◦Software reuse ◦Easy maintenance ◦Implementation flexibility 8
  9. 9. Following are three elements for every OO methodology:  Notation  Process / Method  Tool 9
  10. 10.  Notation: It is collection of graphical symbols for expressing model of the system. The Unified Modeling Language [UML] provides a very robust set of notation which grows from analysis to design. By unifying the notations used by these object oriented methods, the unified modeling language provides the basis for a de facto standard in the domain of object oriented analysis and design founded on a wide base of user experience. 10
  11. 11.  It is a Unified Modeling Language, which is mainly a collection of graphical notation that methods use to express the designs.  The UML is language for visualizing, specifying, constructing and documenting the artifacts of software system.  UML is visual modeling language for modeling systems and is non proprietary.  It is an evolutionary step, which is more expressive and more uniform than individual notations.  Whitehead says “ By relieving the brain of unnecessary work, a good notation, sets it free to concentrate on more advance and creative problems “ UML is not a method or process but is the means to express the same. 11
  12. 12.  System of several different kinds, absolutely anywhere everywhere.  Primarily for software intensive systems like: Systems software Business processes 12
  13. 13.  Captures business processes  Enhance communication and ensures the right communication  Capability to capture the logical software architecture independent of the implementation language  Manages the complexity  Enables reuse of design 13
  14. 14.  UML things: Class, component, node, relationship, package etc..  UML diagrams: Use case diagram, interaction diagram, class diagram, State diagram, deployment diagram 14
  15. 15. What is Process?  It is an extensive set of guidelines that address the technical and organizational aspects of software development focusing on requirements, analysis and design.  Process basically encapsulates the activities leading to the orderly construction of system model.  OO model supports the iterative and incremental model for the process. 15
  16. 16.  Develop software iteratively  Manage requirements  Use component based architectures  Visually model software  Verify S/W quality  Control changes to software. 16
  17. 17.  It is automated support for every stage of software development life cycle.  Since we are concentrating on requirement, analysis and design phase, following are the names of few tools which are greatly in use: 1. Rational Rose 2. Cayenne 3. Platinum 4. Select 5. RSA 17
  18. 18.  Helps designer for creating designs much more quickly.  Supports validations like: Consistency checking Completeness checking Constrain checking.  Time required for certain operation could be predicted .  Code generation  Reverse engineering.  Conversion from SSAD to OOAD  Quick documentation…etc 18
  19. 19.  All three components play equally important role towards the success of the project. 19 Notation Method Tool
  20. 20.  Get introduced with Unified Modeling Language and know the basic components of software development life cycle. 20
  21. 21. 21
  22. 22. 22 STATIC MODEL DYNAMIC MODEL PHYSICAL MODEL LOGICAL MODEL The models of Object Oriented Development
  23. 23.  4+1 view of OO model. ◦ Process view ◦ Deployment view ◦ Logical view ◦ Dynamic view + ◦ Use case view  As shown in the model , for each dimension we define a number of diagrams that denote a view of the system’s model.  The use case view is central since its contents drive the developments of other views. 23
  24. 24. 1. Use case diagram 2. Class Diagram 3. Behavioral diagrams - State chart diagrams - Activity diagrams - Interaction diagrams - Sequence diagrams - Collaboration diagrams 4. Implementation diagrams - Component diagram - Deployment diagram 24
  25. 25.  Use case diagrams represent the functions of a system from the user’s point of view.  Sequence diagrams are a temporal representation of objects and their interactions.  Collaboration diagrams are a spatial representation of objects, links, and interactions.  Object diagrams represent objects and their relationships, and correspond to simplified collaboration diagrams that do not represent message broadcasts.  Class diagrams represent the static structure in terms of classes and relationships. 25
  26. 26. Contd...  State chart diagrams represent the behavior of a class in terms of states  Activity diagrams are to represent the parallel behavior of an operation as a set of actions.  Component diagrams represent the logical components of an application.  Deployment diagrams represent the deployment of components on particular pieces of hardware. 26
  27. 27.  A use case diagram establish the capability of the system as a whole.  Components of use case diagram: Actor Use case System boundary Relationship Actor relationship  Semantic of the components is followed. 27
  28. 28. What is an actor?  An actor is some one or something that must interact with the system under development  UML notation for actor is stickman, shown below. 28 Customer Manager Cashier
  29. 29. More about an actor:  It is role a user plays with respect to system.  Actors are not part of the system they represent anyone or anything that must interact with the system.  Actors carry out use cases and a single actor may perform more than one use cases.  Actors are determined by observing the direct uses of the system. 29
  30. 30. Contd…  Those are responsible for its use and maintain as well as other systems that interact with the developed system.  An actor may - input information to the system. - receive information from the system. - input to and out from the system. 30
  31. 31. How do we find the actor?  Ask following questions to find the actors: ◦ Who uses the system? ◦ Who installs the system? ◦ Who Starts up the system? ◦ What other systems use this system? ◦ Who gets the information from the system? ◦ Who provides information to the system?  Actor is always external to the system. They are never part of the system to be developed. 31
  32. 32. 4-Categories of an actor:  Principle : Who uses the main system functions.  Secondary : Who takes care of administration & maintenance.  External h/w : The h/w devices which are part application domain and must be used.  Other system: The other system with which the system must interact. 32
  33. 33. Note:  If newly identified actor is using a system in a same way like an existing actor, then new actor can be dropped.  If two actors use system in the same way they are same actors. 33
  34. 34. What is USE case?  A use case is a pattern of behavior, the system exhibits  Each use case is a sequence of related transactions performed by an actor and the system in dialogue.  USE CASE is dialogue between an actor and the system.  Examples: 34 Open new account Withdrawal of cash from ATM
  35. 35. More about USE CASE:  It is a snapshot of one aspect of system.  They model a dialog between actor and system.  A use case typically represents a major piece of functionality that is complete from beginning to end.  Most of the use cases are generated in initial phase, but you find some more as you proceed.  A use case may be small or large. It captures a broad view of a primary functionality of the system in a manner that can be easily grasped by non technical user. 35
  36. 36. Contd…  A use case must deliver something of value to an actor.  The use cases may be decomposed into other use cases.  Use cases also present a good vehicle for project planning. 36
  37. 37. How do we find the use cases?  What functions will the actor want from the system?  Does the system store information? What actors will create, read, update. Or delete that information?  Does the system need to notify an actor about changes in its internal state? 37
  38. 38.  Generic format for documenting the use case: - Pre condition: If any ◦ Use case : Name of the case. ◦ Actors : List of actors(external agents), indicating who initiates the use case. ◦ Purpose : Intention of the use case. ◦ Overview : Description. ◦ Type : primary / secondary. ◦ Post condition: If any  Typical Course of Events: ACTOR ACTION : Numbered actions of the actor. SYSTEM RESPONSE : Numbered description of system responses. 38
  39. 39. USE CASE documentation example:  The following use case describes the process of opening a new account in the bank. Use case :Open new account Actors :Customer, Cashier, Manager Purpose :Like to have new saving account. Description :A customer arrives in the bank to open the new account. Customer requests for the new account form, fill the same and submits, along with the minimal deposit. At the end of complete successful process customer receives the passbook. Type :Primary use case. 39
  40. 40.  Those use case functionality which are directly dependent on the system environment are placed in interface objects  Those functionality dealing with storage and handling of information are placed in entity objects  Functionality's specific to one or few use cases and not naturally placed in any of the other objects are placed in control objects By performing this division we obtain a structure which helps us to understand the system from logical view 40
  41. 41. 41 Capture,clarify & validate use cases Analysis Design & Implementation Implement use cases Use cases make up the glue Test Verify that use cases are satisfied
  42. 42. What is System Boundary?  It is shown as a rectangle.  It helps to identify what is external verses internal, and what the responsibilities of the system are.  The external environment is represented only by actors. 42
  43. 43. What is Relationship?  Relationship between use case and actor. Communicates  Relationship between two use cases Extends Include  Notation used to show the relationships: << >> 43
  44. 44.  Relationship between use case and actor is often referred as “communicates” .  Relationship between two use cases is refereed as either include or extends. EXTENDS:  It is used to show optional behavior, which is required only under certain condition. INCLUDE:  It is used to show mandatory behavior, which is required under every condition. 44
  45. 45. Example: Use Case Diagram 45
  46. 46. 46
  47. 47. 47
  48. 48.  To understand and capture the detailed specification of a system to be developed, from user perspective. 48
  49. 49. 49
  50. 50.  Completion of first version of use case diagram initiates the processes of analysis and design.  UML provides the framework to carry out the process of analysis and design in form of set of diagrams.  Every diagram and notation used in the diagram carries the semantics.  First step towards analysis and design is to specify the flow of events. 50
  51. 51.  A flow of events document is created for each use case.  Details about what the system must provide to the actor when the use is executed.  Typical contents ◦ How the use case starts and ends ◦ Normal flow of events ◦ Alternate flow of events ◦ Exceptional flow of events  Typical Course of Events has: Actor Action (AA) System Response (SR) 51
  52. 52. For withdrawal of cash:  1.(SR) The ATM asks the user to insert a card.  2.(AA) The user inserts a cash card.  3.(SR) The ATM accepts the card and reads its serial number.  4.(SR) The ATM requests the password.  5.(AA) The user enters 1234.  6.(SR) The ATM verifies the serial number and password with the bank and gets the notification accordingly.  7.(SA)The ATM asks the user to select the kind of transaction.  8.(AA)User selects the withdrawal. 52
  53. 53. Contd...  9.(SR)The ATM asks for the amount of cash; user enters Rs. 2500/-  10.(SR)The ATM verifies that the amount of cash is within predefined policy limits and asks the bank, to process the transaction which eventually confirms success and returns the new account balance.  11.(SR) The ATM dispenses cash and asks the user to take it.  12.(AA) The user takes the cash.  13.(SR) The ATM asks whether the user wants to continue.  14.(AA) The user indicates no. 53
  54. 54. Contd...  15.(SR) The ATM prints a receipt, ejects the card and asks the user to take them  16.(AA) The user takes the receipt and the card.  17.(SR) The ATM asks a user to insert a card. 54
  55. 55. For withdrawal of cash use case:  9. The ATM asks for the amount of cash; the user has change of mind and hits the “cancel”. 55
  56. 56. For withdrawal of cash use case:  3 Suspicious pattern of usage on the card.  10 The machine is out of cash.  11 Money gets stuck in the machine. 56
  57. 57.  It helps in understanding the functionality of a system to be developed.  Flow of events helps in finding objects of the system to be developed.  Happens to be most important and very first step towards analysis and design. 57
  58. 58.  The functionality of the use case is captured in flow of the events.  A scenarios is one path through the flow of events for the use case.  Scenarios are developed to help identify objects, classes and object interactions for that use case. 58
  59. 59. 59 Example: 0 Level DFD
  60. 60. 60 Example: Level 1 DFD
  61. 61. 61 Example: Level 2 DFD
  62. 62.  To understand the flow of each functionality and find out the objects and methods required to build the system. 62
  63. 63. 63
  64. 64.  The use case diagram presents an outside view of the system  Interaction diagrams describe how use cases are realized as interactions among societies of objects.  Two types of interaction diagrams ◦ Sequence diagrams ◦ Collaboration diagrams 64
  65. 65.  Interaction diagrams are models that describe how groups of objects collaborate in some behavior  There are 2 kinds of interaction diagrams • Sequence diagram • Collaboration diagram  Sequence diagrams are a temporal representation of objects and their interactions  Collaboration diagrams are spatial representation of objects, links and interrelations 65
  66. 66.  Typically these diagrams capture behaviors of the single scenario.  Shows object interaction arranged in time sequence.  They show sequence of messages among the objects.  It has two dimensions, vertical represents time & horizontal  represents objects.  Components of sequence diagram: -objects -object lifeline -Message -pre/post conditions. 66
  67. 67. 67  Object are represented by rectangles and name of the objects are underlined.  Object life line are denoted as dashed lines. They are used to model the existence of objects over time. Name:Class
  68. 68.  They are used to model the content of communication between objects. They are used to convey information between objects and enable objects to request services of other objects.  The message instance has a sender, receiver, and possibly other information according to the characteristics of the request.  Messages are denoted as labeled horizontal arrows between life lines.  The sender will send the message and receiver will receive the message. 68
  69. 69. Contd…  May have square brackets containing a guard conditions. This is a Boolean condition that must be satisfied to enable the message to be sent.  May have an asterisk followed by square brackets containing an iteration specification. This specifies the number of times the message is sent.  May have return list consisting of a comma -separated list of names that designate the values of returned by the operation.  Must have a name or identifier string that represents the message.  May have parentheses containing an argument list consisting of a comma separated list of actual parameters passed to a method. 69
  70. 70. 70 :Customer :ATM :Bank Request password Verify account Enter the password Account o.k. Request option Enter option Request amount Enter the amount Update transaction Transaction commit Insert card Dispense cash Request take cash Take cash Request continuation Terminate Print receipt ,eject card Request take card Take card Display main screen and prompt for the card. :Transaction Create Transaction Transaction complete Sequence diagram [for withdrawal of cash, normal flow]
  71. 71. 71 Example: Sequence Diagram
  72. 72.  Collaboration diagrams illustrate the interaction between the objects, using static structure.  Unlike sequence diagram the time is not explicitly represented in these diagrams  In collaboration diagram the sequence of messages is indicated by numbering the messages. The UML uses the decimal numbering scheme.  In these diagrams, an actor can be displayed in order to represent the triggering of interaction by an element external to the system.  This helps in representing the interaction, without going into the details of user interface. 72
  73. 73.  Named objects  Links: Links are represented by a continuous line between objects, and indicates the exchange of messages.  Messages has following attributes:  Synchronization --thread name, step within thread.  Sequence number  Message labels : The name of the message often corresponds to an operation defined in the class of the object that is the destination of the message. Message names may have the arguments and return values.  *[iteration].  It uses decimal notation.  Message direction. 73
  74. 74.  Object names identify which objects are participating and the links show which objects collaborate  A link between two objects must exist for one object to send message to another and vice a versa.  Messages in the collaboration diagram get transformed to more detailed signature.  They use the decimal notation system for numbering the messages.  The direction of the message defines the sender and receiver of the message 74
  75. 75.  Predecessor  Role names  Message qualifiers ◦ Iteration expression ◦ Parameters ◦ Return values ◦ Message stereotypes  Concurrent thread sequencing  Thread dependencies  Message expression [Pre] A1:*(expression):doIt(p,r):return value 75
  76. 76. 4:Display(x,y) Simple message 3.3.1:Display(x,y) Nested message 4.2:subtract[Today,Birthday]:age Nested message with return value [Age >=18] 6.2:Vote() Conditional message 4.a,b.6/c.1:Turnon(Lamp) Synchro. with other flow of execution 1*:wash() Iteration 3.a,3.b/4*||[i:=1..n]:Turnoff() Parallel iteration 76
  77. 77. 77 1. Insert card Enter password, Enter kind Enter amount, Take cash, Take card cancel,Terminate, Continue Display main screen unreadable card message, request password, request kind, request amount, canceled message, eject card, failure message, dispense cash, request take cash request continuation, print receipt, request take card bad account message, bad bank account message Verify account, process transaction Transaction succeed Transaction failed account o.k. bad account, bad password, bad bank code Create Transaction Transaction complete CUST- OMER BANK ATM TRANSA- CTION
  78. 78. 78 Example: Collaboration Diagram
  79. 79.  To know the interaction among the objects in temporal and spatial form.  To know how objects collaborate among each other and hence delegate the responsibility to the respective objects.  To understand how the messages get matured with more information. 79
  80. 80. 80
  81. 81.  A class diagram shows the existence of classes and their relationships in the logical view of a system  UML modeling elements in class diagrams are: ◦ Classes, their structure and behavior. ◦ relationships components among the classes like association, aggregation, composition, dependency and inheritance ◦ Multiplicity and navigation indicators ◦ Role names or labels. 81
  82. 82.  Association  Aggregation  Composition  Inheritance  Dependency 82
  83. 83. These are the most general type of relationship:  It denotes a semantic connection between two classes  It shows BI directional connection between two classes  It is a weak coupling as associated classes remain somewhat independent of each other  Example: 83 CUSTOMER ATM system
  84. 84. This is a special type of association  The association with label “contains” or “is part of” is an aggregation  It represents “has a “ relationship  It is used when one object logically or physically contains other  The container is called as aggregate  It has a diamond at its end  The components of aggregate can be shared with others  It expresses a whole - part relationships 84
  85. 85. 85 Example: Customer ATM card
  86. 86. This is a strong form of aggregation  It expresses the stronger coupling between the classes  The owner is explicitly responsible for creation and deletion of the part  Any deletion of whole is considered to cascade its part  The aggregate has a filled diamond at its end 86 Window Client Area
  87. 87.  The inheritance relationship helps in managing the complexity by ordering objects within trees of classes with increasing levels of abstraction. Notation used is solid line with arrowhead,shown below.  Generalization and specialization are points of view that are based on inheritance hierarchies. 87 Account SavingAccountCurrentAccount
  88. 88.  Dependency is semantic connection between dependent and independent model elements.  This association is unidirectional and is shown with dotted arrowhead line.  In the following example it shows the dependency relationship between client and server.  The client avails services provided by server so it should have semantic knowledge of server.  The server need not know about client. 88 Client Server
  89. 89. Definition: Number of instances of each class involved in the dialogue is specified by cardinality.  Common multiplicity values:  Symbol Meaning  1 One and only one  0..1 Zero or one  M…N From M to N (natural integer)  0..* From zero to any positive integer  1..* From one to any positive integer  Also thought can be given about navigability to every applicable relationship. 89
  90. 90.  In collaboration diagram we have shown the objects, their interaction and detailed message signature.  This information is carried forward to the class diagram.  At this point,we group the similar objects and form classes.  Messages get mapped to responsibilities for respective classes.  Find the attributes for every class.  Transform the links to appropriate relationships.  Relationship is further refined with respect to multiplicity and navigability. This complete procedure brings the minimal class diagram [for withdraw cash use case, normal flow.] 90
  91. 91. 91 Customer Transaction 1 0..* 1 0..* ATMSystem 1..* 1..* 1..* 1..* Bank[Branch] 1 1..* 1 1..* 1 1 1 1
  92. 92.  Till this slide we have worked out the essentials of class diagram for withdrawal of cash use case, normal flow of events.  Similar exercise required to be carried out for every scenario and clubbed all in the class diagram.  At this point, we refine this integrated class diagram to add further fine details. Approximate sketch for this class diagram has been shown at the end of this module.  Refinement attributes should be updated right from sequence diagram to class diagram.  Next few slides will take into the discussion of refinement attributes.  This process of iterative and incremental development will continue till there is no change in two consecutive iteration. 92
  93. 93. 93 Identify objects Identify Messages Group Objects into classes Identify & classify Class relationships Identify class behavior Group classes into domains Validate Classes & Objects
  94. 94. 94 Example: Class Diagram
  95. 95.  Learn to build the architecture, which contains the entire information of the system to be developed.  It is this architecture which is called as BLUE PRINT is handed over for coding. 95
  96. 96. 96
  97. 97.  A state transition diagram shows the states of a single object, the events or the messages that cause a transition from one state to another and the action that result from a state change.  A state transition diagram will not be created for every class in the system. Components of State Diagram: ◦ Start State ◦ Stop state ◦ State Transition 97
  98. 98.  State: A state is a condition during the life of an object when it satisfies some condition, performs some action, or waits for an event. The UML notation for a state is a rectangle with rounded corners.  Special states: There are two special states. Start state: Each state diagram must have one and only one start state. Notation for start state is “filled solid circle”. Stop State: An object can have multiple stop states. Notation for stop state is bull’s eye. 98
  99. 99. Contd...  State transition: A state transition represents a change from an originating to a successor state.  Transition label: event name[guard condition] / action 99
  100. 100. 100 Example: State Chart Diagram
  101. 101. 101 Example: State Chart Diagram
  102. 102. 102 Example: State Chart Diagram
  103. 103.  A state diagram will not be created for every class.  state diagrams are used only for those classes that exhibit interesting behavior.  State diagrams are also useful to investigate the behavior of user interface and control classes.  State diagram are used to show dynamics of a individual class 103
  104. 104. It is a special kind of state diagram and is worked out at use case level.  These are mainly targeted towards representing internal behavior of a a use case.  These may be thought as a kind of flowchart.  Flowcharts are normally limited to sequential process; activity diagrams can handle parallel process.  Activity diagrams are recommended in the following situations:  Analyzing use case  Dealing with multithreaded application  Understanding workflow across many use cases. 104
  105. 105. Consistency checking is the process of ensuring that information in both static view of the system(class diagram) and the dynamic view of the system(sequence and collaboration diagram) is telling the same story. 105
  106. 106. 106 Example: Activity Diagram
  107. 107.  Understand the dynamic behavior of a class  Way to find the parallel processes at use case level. 107
  108. 108. 108
  109. 109. COMPONENT DIAGRAM: Component diagrams illustrate the organizations and dependencies among software components. A component may be  A source code component  A run time components  An executable component  Dependency relationship. 109
  110. 110. 110 policy.dll Branch Bank.dllcustomer.dll ATM.exe Branch Bank.exe Bank Server.exe
  111. 111. 111 Example: Component Diagram
  112. 112. 112 Example: Modeling
  113. 113.  A deployment diagram shows the relationship among software and hardware components in the delivered system.  These diagram include nodes and connections between nodes.  Each node in deployment diagram represents some kind of computational unit, in most cases a piece of hardware.  Connection among nodes show the communication path over which the system will interact.  The connections may represent direct hardware coupling line RS-232 cable, Ethernet connection, they also may represent indirect coupling such as satellite to ground communication. 113
  114. 114. 114 ATM_ machine Bank_ server Branch Bank_ Ethernet Ethernet Bank.exe BankServer.exe ATM.exe
  115. 115. 115 Example: Deployment Diagram
  116. 116.  To understand the organization of software modules and their deployment on the respective hardware. 116
  117. 117. 117
  118. 118. It may be: 1.Calendar Centric 2.Requirement Centric 3.Documentation Centric 4.Quality Centric 5.Architecture Centric 118
  119. 119.  Architecture driven projects represent the most mature style of development.  These projects are characterized by a focus on creating a frame work that satisfies all known requirement, yet is resilient enough to adapt to those requirements, that are not yet known or well understood.  In every sense of the word, architect-driven policies are in evolutionary step beyond requirement driven policies.  Architecture driven style of development is usually the best approach for the creation of most complex software intensive systems 119
  120. 120. Architecture driven style of development typically observe the following process: 1. Specify the system’s desired behavior through a collection of scenarios. (Analysis) 2. Create, then validate, an architecture. (Design) 3. Evolve that architecture, making mid-course corrections as necessary to adopt to new requirements as they are uncovered. 120
  121. 121. What exactly is nature of the well structured object oriented architecture?? 1. A set of classes, typically organized into multiple hierarchies. 2. A set of collaboration that specify how those classes co-operate to provide various system function. 121
  122. 122. Use case driven Architecture centric Incremental and iterative approach. 122