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Software engineering


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Software engineering

  1. 1. UNIT I Introduction to Software Engineering Presented By Prof.Hitesh Mohapatra Dept. of Computer Engg.
  2. 2. Software’s Dual Role  Software is a product    Delivers computing potential Produces, manages, acquires, modifies, displays, or transmits information Software is a vehicle for delivering a product     Supports or directly provides system functionality Controls other programs (e.g., an operating system) Effects communications (e.g., networking software) Helps build other software (e.g., software tools)
  3. 3. What is Software? Software is a set of items or objects that form a “configuration” that includes • programs • documents • data ...
  4. 4. What is Software?    software is engineered software doesn’t wear out software is complex
  5. 5. Wear vs. Deterioration in re s d fa re c ae ilu ra d e to s e e c te u id ffe ts F ilue a r rt ae cag hne a t ac r e cu l uv id a e c r e e liz d uv T e im
  6. 6. Software Applications        system software application software engineering/scientific software embedded software product-line software Web Apps (Web applications) AI software
  7. 7. Software—New Categories     Ubiquitous computing—wireless networks Net sourcing—the Web as a computing engine Open source—”free” source code open to the computing community (a blessing, but also a potential curse!) Also … (see Chapter 32)     Data mining Grid computing Cognitive machines Software for nanotechnologies
  8. 8. Legacy Software Why must it change?     software must be adapted to meet the needs of new computing environments or technology. software must be enhanced to implement new business requirements. software must be extended to make it interoperable with other more modern systems or databases. software must be re-architected to make it viable within a network environment.
  9. 9. Software Myths  Management Myths      Customer myths    We have books of standards, my staff will have sufficient info. I work very hard to put the latest, greatest, fastest, state-of-the-art hardware in front of all my programmers. We have the greatest CASE tools around. If we get behind, we can just add more programmers. A general statement of objectives is sufficient to start coding, fill in the details later. Project requirements change constantly, but change is easy because software is flexible. Programmer myths    Once the program is written and working, our job is done. Until the program is running, there is no way to assess quality. The only deliverable for a successful project is the working program.
  10. 10. Software Engineering Practice Software engineering practice - Communication practices - Planning practices - Analysis modeling practices - Design modeling practices - Construction practices - Deployment practices -
  11. 11. Software Engineering Practice     Consists of a collection of concepts, principles, methods, and tools that a software engineer calls upon on a daily basis Equips managers to manage software projects and software engineers to build computer programs Provides necessary technical and management how to’s in getting the job done Transforms a haphazard unfocused approach into something that is more organized, more effective, and more likely to achieve success
  12. 12. The Essence of Problem Solving Understand the problem (communication and analysis) 1) • • • • Who has a stake in the solution to the problem? What are the unknowns (data, function, behavior)? Can the problem be compartmentalized? Can the problem be represented graphically? Plan a solution (planning, modeling and software design) 1) • • • Have you seen similar problems like this before? Has a similar problem been solved and is the solution reusable? Can sub problems be defined and are solutions available for the sub problems?
  13. 13. The Essence of Problem Solving (continued) Carry out the plan (construction; code generation) 3) • • Does the solution conform to the plan? Is the source code traceable back to the design? Is each component of the solution correct? Has the design and code been reviewed? Examine the results for accuracy (testing and quality assurance) 3) • • Is it possible to test each component of the solution? Does the solution produce results that conform to the data, function, and behavior that are required?
  14. 14. Seven Core Principles for Software Engineering 1) Remember the reason that the software exists • 1) Keep it simple, stupid (KISS) • 1) Never design yourself into a corner; build software that can be easily changed and adapted Plan ahead for software reuse • 1) Always specify, design, and implement knowing that someone else will later have to understand and modify what you did Be open to the future • 1) A clear vision is essential to the project’s success Others will consume what you produce • 1) All design and implementation should be as simple as possible Maintain the vision of the project • 1) The software should provide value to its users and satisfy the requirements Reuse of software reduces the long-term cost and increases the value of the program and the reusable components Think, then act • Placing clear, complete thought before action will almost always produce better results
  15. 15. Communication Practices (Requirements Elicitation) Communication Project initiation Requirements gathering Planning Estimating Scheduling Modelling Analysis Tracking Design Construction Code Test Deployment Delivery Support Feedback 15
  16. 16. Communication Principles 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) Listen to the speaker and concentrate on what is being said Prepare before you meet by researching and understanding the problem Someone should facility the meeting and have an agenda Face-to-face communication is best, but also have a document or presentation to focus the discussion Take notes and document decisions Strive for collaboration and consensus Stay focused on a topic; modularize your discussion If something is unclear, draw a picture Move on to the next topic a) after you agree to something, b) if you cannot agree to something, or c) if a feature or function is unclear and cannot be clarified at the moment Negotiation is not a contest or a game; it works best when both parties win
  17. 17. Planning Practices (Defining a Road Map) Communication Project initiation Requirements gathering Planning Estimating Scheduling Modelling Tracking Analysis Design Construction Code Test Deployment Delivery Support Feedback 17
  18. 18. Planning Principles 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) Understand the scope of the project Involve the customer in the planning activity Recognize that planning is iterative; things will change Estimate based only on what you know Consider risk as you define the plan Be realistic on how much can be done each day by each person and how well Adjust granularity as you define the plan Define how you intend to ensure quality Describe how you intend to accommodate change Track the plan frequently and make adjustments as required
  19. 19. Barry Boehm’s W5HH Principle        Why is the system being developed? What will be done? When will it be accomplished? Who is responsible for each function? Where are they organizationally located? How will the job be done technically and managerially? How much of each resource is needed? The answers to these questions lead to a definition of key project characteristics and the resultant project plan.
  20. 20. Modeling Practices (Analysis and Design) Communication Project initiation Requirements gathering Planning Estimating Scheduling Tracking Modelling Analysis Design Construction Code Test Deployment Delivery Support Feedback
  21. 21. Analysis Modeling Principles 1) 2) 3) 4) 5) The information domain of a problem (the data that flows in and out of a system) must be represented and understood The functions that the software performs must be defined The behavior of the software (as a consequence of external events) must be represented The models that depict information, function, and behavior must be partitioned in a manner that uncovers detail in a layered (or hierarchical) fashion The analysis task should move from essential information toward implementation detail
  22. 22. Design Modeling Principles 1) 2) 3) 4) 5) 6) 7) 8) 9) The design should be traceable to the analysis model Always consider the software architecture of the system to be built Design of data is as important as design of processing functions Interfaces (both internal and external) must be designed with care User interface design should be tuned to the needs of the end-user and should stress ease of use Component-level design should be functionally independent (high cohesion) Components should be loosely coupled to one another and to the external environment Design representations (models) should be easily understandable The design should be developed iteratively; with each iteration, the designer should strive for greater simplicity External quality factors: those properties that can be readily observed Internal quality factors: those properties that lead to a high-quality design from a technical perspective
  23. 23. Construction Practices Communication Project initiation Requirements gathering Planning Estimating Scheduling Tracking Modelling Analysis Constructio Design n Code Test Deployment Delivery Support Feedback
  24. 24. Coding Principles (Preparation before coding) 1) 2) 3) 4) 5) Understand the problem you are trying to solve Understand basic design principles and concepts Pick a programming language that meets the needs of the software to be built and the environment in which it will operate Select a programming environment that provides tools that will make your work easier Create a set of unit tests that will be applied once the component you code is completed
  25. 25. Coding Principles (As you begin coding) 1) 2) 3) 4) 5) 6) 7) 8) Constrain your algorithms by following structured programming practices Select data structures that will meet the needs of the design Understand the software architecture and create interfaces that are consistent with it Keep conditional logic as simple as possible Create nested loops in a way that makes them easily testable Select meaningful variable names and follow other local coding standards Write code that is self-documenting Create a visual layout (e.g., indentation and blank lines) that aids code understanding
  26. 26. Coding Principles 1) 2) 3) (After completing the first round of code) Conduct a code walkthrough Perform unit tests (black-box and white-box) and correct errors you have uncovered Refactor the code
  27. 27. Testing Principles 1) 2) 3) All tests should be traceable to the software requirements Tests should be planned long before testing begins The Pareto principle applies to software testing • 1) Testing should begin “in the small” and progress toward testing “in the large” • 1) 80% of the uncovered errors are in 20% of the code Unit testing --> integration testing --> validation testing --> system testing Exhaustive testing is not possible .
  28. 28. Test Objectives 1) 2) 3) Testing is a process of executing a program with the intent of finding an error A good test case is one that has a high probability of finding an asyet undiscovered error A successful test is one that uncovers an as-yet undiscovered error
  29. 29. Deployment Practices Communication Project initiation Requirements gathering Planning Estimating Scheduling Tracking Modelling Analysis Design Construction Code Test Deployment Delivery Support Feedback
  30. 30. Deployment Principles 1) Customer expectations for the software must be managed • 1) 2) 3) 4) Be careful not to promise too much or to mislead the user A complete delivery package should be assembled and tested A support regime must be established before the software is delivered Appropriate instructional materials must be provided to end users Buggy software should be fixed first, delivered later
  31. 31. Software Process
  32. 32. Process Models   Waterfall model Incremental Process Models    Evolutionary Process Models    Prototyping model Spiral model Specialized Process Models    Rapid application development model Incremental model Component-Based Development Formal Method model Comparison of life-cycle models
  33. 33. Waterfall model    Requirements are reasonably understood. When work flow is linear in fashion Systematic sequential approach
  34. 34. r) r) (o e (o el l de y cl M od o c l M ife ti a l l rfa a l L ue n a te sic e q W as S C l ne a r Li
  35. 35. Incremental model    Evolution of waterfall model New features added to 1st Increment(core product) Incremental software development model may be applicable to projects where:   Software Requirements are well defined, but realization may be delayed. The basic software functionality are required early
  36. 36. SW Functionality and features Time Inc 1 Inc 2 Inc 3
  37. 37. RAD Model         Rapid Application Development Short development cycle Faster development (60-90) days High quality results Use of (CASE) Tools Component based construction System delivered in short time (2 to 3 months) Useful where requirements are well understood and scope is limited
  38. 38. The RAD Model Team # n M o d e lin g bus ines s m odeling dat a m odeling proc es s m odeling C o n s t r u c t io n c om ponent reus e aut om at ic c ode generat ion t es t ing Team # 2 Com m unicat ion Mo d eling b u si n e ss m o d e l i n g dat a m odeling p ro ce ss m o d e l i n g Planning Co nst r uct io n Team # 1 co m p o n e n t re u se a u t o m a t i c co d e g e n e ra t i o n t e st i n g Mode ling De ploym e nt int egrat ion deliv ery feedback business modeling dat a modeling process modeling Const r uct ion component reuse aut omat ic code generat ion t est ing 6 0 - 9 0 days 40
  39. 39. Process Models   Waterfall model Incremental Process Models    Evolutionary Process Models      Prototyping model Spiral model Specialized Process Models   Rapid application development model Incremental model Component-Based Development Formal Method model Unified Process Comparison of life-cycle models
  40. 40. Prototyping      Early approximation of a final system Linear and iterative Customer is unable to define the system Requirements are not freezed a prototype is built to understand the requirements
  41. 41. Evolutionary Models: Prototyping Qu ick p lan Quick Com m unicat ion plan communication Mo d e lin g Modeling Qu ick d e sig n Quick design Deployment Deployment De live r y delivery & & Fe e dback feedback Const r uct ion Construction of of prototype pr ot ot ype 43
  42. 42. Spiral Model  Simplified form   Precede each phase by    Waterfall model plus risk analysis Alternatives Risk analysis Follow each phase by   Evaluation Planning of next phase
  43. 43. Evolutionary Models: The Spiral planning estimation scheduling risk analysis communication modeling analysis design start deployment delivery feedback construction code test 45
  44. 44. Specialized Process Models 1)Component Based Development  COTS   Commercial off-the-shelf software components developed by vendors who offer them as products. Decomposition of the engineered systems into functional or logical components with well-defined interfaces used for communication across the components.
  45. 45. Co De m M s ig p on C o odu n e n m le a r c t i n pr I n h te e h te ite g e n ge ct u r a t s i ra r e ion ve tio te n. st in g.
  46. 46. 2) Formal Methods Model   Mathematically based techniques for representing and analysis of software. Formal methods include     Formal specification Specification analysis and proof Transformational development Program verification
  47. 47. Formal Methods Model      Reduces requirements errors as it forces a detailed analysis of the requirements Incompleteness and inconsistencies can be discovered and resolved Currently very time consuming and expensive Extensive training required Difficult to use this model to communicate with the customer.
  48. 48. Unified Process   Contains features of OOA and OOD. UML- Unified Modeling Language   It was created to support the OO design and modeling. iterative and incremental process
  49. 49. Phases of Unified process All the phases are concurrent in nature  Inception  Elaboration  Construction  Transition  Production
  50. 50. The Unified Process (UP) Elab o r at io n elaboration Incep t inceptionio n inception co nst r uct io n Release soft ware increment t r ansit io n p r o d uct io n 52
  51. 51. UP (contd)  Inception   Customer communication Planning   Business requirements are identified   Identify resources, assess risks, defines schedule In the form of use cases. Rough architecture  A tentative outline of major sub-systems, functions and features that populate them.
  52. 52. UP (contd)  Elaboration     Customer communication Modeling activity Expands the use cases. Expands the architecture to:   Use case model, analysis model, design model, implementation model and deployment model. Review plan and make modifications  Evaluate scope, risks, project delivery dates
  53. 53. UP (contd)  Construction      Develop software components (that make the use cases operational). Complete the analysis and design models. Implement all functions and features for that increment. Conduct unit testing for the components Integrate components.
  54. 54. UP (contd)  Transition     Create user manuals, guidelines, installation procedures. Software is given to users for beta testing. Get user feedback The increment is now a useable software release.
  55. 55. Incept ion phase Vision document Init ial use-case model Init ial project glossary Init ial business case Init ial risk assessment . Project plan, phases and it erat ions. Business model, if necessary . One or more prot ot y pes I nc e pt i o n UP Work Products Elaborat ion phase Use-case model Supplement ary requirement s including non-funct ional Analy sis model Soft ware archit ect ure Descript ion. Execut able archit ect ural prot ot y pe. Preliminary design model Rev ised risk list Project plan including it erat ion plan adapt ed workflows milest ones t echnical work product s Preliminary user manual Const ruct ion phase Design model Sof t ware component s Int egrat ed soft ware increment Test plan and procedure Test cases Support document at ion user manuals inst allat ion manuals descript ion of current increment Transit ion phase Deliv ered soft ware increment Bet a t est report s General user feedback 57
  56. 56. Agile Software Development    Is a group of software development methodologies based on iterative and incremental development, where requirements and solutions evolve through collaboration between self-organizing, cross-functional teams. Self Organization: is the process where a structure or pattern appears in a system without central authority. Cross-Functional team : is a group of people with different functional expertise working toward a common goal.
  57. 57. Extreme Programming       Is a software development methodology which is intended to improve software quality and responsiveness to changing customer requirements. It releases product in short development cycles (time boxing) Pair Programming: Driver and Observer Time Boxing Code Review Unit Testing