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Software Evolution_Se lect3 btech


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Software Evolution_Se lect3 btech

  1. 1. Types of software products 1
  2. 2. Syllabus: Unit 1• Role of Software Engineering, Software Evolution, Legacy system structures, Legacy system design, Legacy System Assessment, Software Development Life Cycle. 2
  3. 3. Difference between generic and customized software • The generic software product specifications are produced internally by the marketing department of the product company. They reflect what they think will sell. They are usually flexible and non-prescriptive. • For customized systems are often the basis for the contract between customer and developer. They are usually defined in detail and changes have to be negotiated and carefully costed. 3
  4. 4. What are the main ingredients ofSoftware Engineering. 4
  5. 5. What are the main ingredients ofSoftware Engineering• Principle• Methods and Techniques• Methodology• Tools• How above are correlated… 5
  6. 6. • Relationship Between Principal, Methods and Techniques, Methodology and Tools 6
  7. 7. What are the key challenges facingsoftware engineering? 7
  8. 8. What are the key challenges facingsoftware engineering?• Heterogeneity, delivery and trust.• Heterogeneity – Developing techniques for building software that can cope with heterogeneous platforms and execution environments;• Delivery – Developing techniques that lead to faster delivery of software;• Trust – Developing techniques that demonstrate that software can be trusted by its users. 8
  10. 10. Software change• Software change is a common requirement – New requirements emerge when the software is used; – The business environment changes; – Errors must be repaired; – New computers and equipment is added to the system; – The performance or reliability of the system may have to be improved.• A key problem for organisations is implementing and managing change to their existing software systems. 10
  11. 11. Importance of evolution• Organisations have huge investments in their software systems - they are critical business assets.• To maintain the value of these assets to the business, they must be changed and updated.• The majority of the software budget in large companies is devoted to evolving existing software rather than developing new software. 11
  12. 12. Spiral model of evolution Specification Implem ention Star t Release 1 Operation Validation Release 2 Release 3 12
  13. 13. Program evolution dynamics• Program evolution dynamics is the study of the processes of system change.• After major empirical studies, Lehman and Belady proposed that there were a number of ‘laws’ which applied to all systems as they evolved.• There are sensible observations rather than laws. They are applicable to large systems developed by large organisations. Perhaps less applicable in other cases. 13
  14. 14. Evolution processes• Evolution processes depend on – The type of software being maintained; – The development processes used; – The skills and experience of the people involved.• Proposals for change are the driver for system evolution. Change identification and evolution continue throughout the system lifetime. 14
  15. 15. Change identification and evolution Change identification process New sy stem Change proposals Software evolution process 15
  16. 16. The system evolution process Change Im pact Release Change Sy stem requests anal y sis planning im plem enta tion release Platform Sy stem Fault repair adaptation enhancem ent 16
  17. 17. Change implementation Proposed Requirements Requir ements Software changes analy sis upda ting de velopm ent 17
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  26. 26. What are legacy systems?• Systems developed for a specific client that have been in service for a long-time• Many of these systems were developed years ago using obsolete technologies• They are likely to be business critical systems required for normal operation of a business• These are the systems that everyone worried about when the Y2K concerns became public 26
  27. 27. Background to legacy systems • Software systems are a major investment • Systems may be long lived to obtain return on investment (ROI) and thus become “legacy in nature” • They may be critical for operation of an organisation • Legacy systems may have evolved over many years (customisations) 27
  28. 28. Definition• A ‘Legacy System’ refers to any computer system (typically, although not always a mini or mainframe computer system), which has been in existence for a long time.• ‘Legacy Data’ relates to information collected by an organisation, which is of value to that organisation, but which has been created or stored by the use of software and/or hardware that has been rendered outmoded or obsolete. 28
  29. 29. Socio Technical Systems• Legacy Systems have been called “Socio Technical Systems” – Systems that include technical systems but also operational processes and people who use and interact with the technical system. Socio-technical systems are governed by organizational policies and rules. 29
  30. 30. Causal Dimensions of LegacyStatus • System suitability System – Suitability to organisation’s Suitability missionUnderlying – Suitability to organisation platform structure – Suitability to process • Underlying platform Software – Hardware, Operating system, Quality Networking, Development environment and Data management • Software quality – Component quality – Design quality – Change management quality30
  31. 31. Legacy Effects– Asset value goes down – Ease of maintenance • Mission criticality declines • reliability • Cost of maintenance and– Ease of operation goes down resistance to it • User satisfaction • Availability of resources • Ease of testing and auditing • Program size and complexity– Ease of migration / evolution • Dependence on individuals declines • Ease of use of new technology • Scalability 31
  32. 32. Finding a solution• Slee and Slovin (1997) proposed a 4R portfolio matrix: - Low business value Low business value Low technology condition High technology condition Retire Reassess High business value High business value Low technology condition High technology condition Redevelop Renew 32
  33. 33. Legacy System Replacement • The business risks associated with the strategy of scrapping a legacy system and replacing it with a new one are not insignificant – legacy systems rarely have complete specifications – changes are not likely to be documented well at all – business processes are reliant on the system – the legacy system may contain embedded business rules that are not formally documented elsewhere – software development is risky and not is always successful 33
  34. 34. Changing Legacy Systems • All systems must change to remain useful • Changes to legacy systems can be very expensive – components may be implemented with different programming styles as changes are implemented – system may be written in an obsolete language – system documents often out-of-date – system structure may be corrupted by years of maintenance activities – techniques used to save space or increase speed may have obscured understandability – file structures used may be incompatible with each other 34
  35. 35. Legacy System Risks• Replacing a legacy system is both expensive and risky• Maintaining a legacy system is also expensive and risky• Sometimes a the decision is made (based on the costs and risks involved) to extend system life-time using techniques like re-engineering 35
  36. 36. Socio-Technical Systems• Lagacy systems are more than just software systems• Sommerville describes legacy systems as socio- technical systems• Socio-Technical System Layers – business processes – application software – support software – hardware 36
  37. 37. Legacy System Structures • System Hardware – could be a mainframe • System Software • Application Software • Application Data – business critical data often used by several programs • Business Processes – processes that support a business objective and rely on the legacy systems hardware and software • Business Policies and Rules – business operation constraints 37
  38. 38. Legacy System Components E beds m know dge of le Uses Sup port Application Busin po ess licies software softw are and rulesRuns-on Runs-on Uses Uses Constrains System Application Business ha are rdw data processes 38
  39. 39. System Change• In theory – it should be possible to replace one layer in a socio-technical system without making any changes to the other layers• In practice – changing one layer introduces new facilities that must be used in higher level layers – changing the software may require hardware changes to maintain system performance – it may be impossible to maintain hardware interfaces because of the huge differences between mainframe and client-server architectures 39
  40. 40. Legacy Application SystemPro am1 gr Program2 Program3 File 1 File 2 File 3 File 4 File 5 File 6 Pro am4 gr Pr am5 ogr Program6 Program7 40
  41. 41. Database Management System P gra ro m Pogr m r a P gra ro m Pogr m r a 1 2 3 4 D ta a a b se d sc s e ribe Logic l a d a n m n ge e t a a mn ph ic l ys a sy m ste da m de ta o ls 41
  42. 42. Transaction Processing Account queries and updates Serialised transactions Teleprocessing Accounts monitor databaseATMs and terminals 42
  43. 43. Architecture • Component based – Not necessarily object-oriented – Good software component and design quality • Object oriented – Good software component and design quality – Infrastructures may be too ‘leading edge’ • Layered architecture – Promotes flexibility in adapting applications – Requires sophisticated understanding of platforms 43
  44. 44. Dilemma• Businesses with multiple legacy systems face a dilemma – Continue using Legacy systems - increased maintenance costs. – Replace Legacy Systems - costly, risks associated with changing business systems• Alternative is to use modern software engineering techniques to extend lifetime of legacy systems 44
  45. 45. Legacy System Categories • Low quality, Low business value – scrap the system • Low quality, High business value – should be re-engineered or replaced if a suitable system is available • High-quality, Low business value – Replace or scrap system, or maintain • High-quality, High business value – continue operation using normal maintenance practices 45
  46. 46. Legacy System Assessment• Strategies for obtaining best ROI – Scrap Legacy System : system is not making a contribution to business – Continue maintaining system: system is stable and minimal changes being requested – Transform system to improve maintainability: changes are degrading quality and changes are still required – Replace System: modern systems / technology provide a viable cost effective alternative 46
  47. 47. Legacy System Assessment • Low quality, low business value: Expensive to maintain with low business value so candidates for scrapping. • Low quality, high business value: Expensive to maintain but high business value thus cannot be scrapped. Candidates for system transformation or replacement. • High quality, low business value: Inexpensive to maintain with low business value. Avoid risk of replacement by maintaining or scrapping. • High quality, high business value: Must be kept in operation; high quality so transformation or system replacement not necessary. Maintain system. 47
  48. 48. Business Value Assessment • Establish business value of legacy system by consulting: – End-users: establish level of system usage and perceived effectiveness. – Customers: establish level of transparency; flexibility; responsiveness; errors – Line managers: Establish benefits to business unit; are costs justified; criticality of system. – IT managers: Establish skills availability; level of resource usage – Senior managers: Establish the level of the systems contribution to the business goals 48
  49. 49. Business Value Assessment • System usage: if legacy system usage is low then it has a low business value. • Business processes: legacy system may not be flexible in accommodating changing business processes, thus has a low business value • System dependability: if legacy system is unreliable then it has a low business value • System outputs: business depends on legacy system outputs (high business value), if output can be produced in alternate way (low business value) 49
  50. 50. Environmental Assessment • Supplier stability: Still in existence? Financially stable? Alternate supplier providing system maintenance? • Failure rate: Level of failure (reboot v’s random app failure). Hardware / software failures. • Age: With age comes obsolescence, increased maintenance costs • Performance: Is performance adequate? • Support requirements: Is a high level of support required? Are costs high? • Maintenance costs: Costs of hardware/software maintenance increase with system age. • Interoperability: Are there issues interfacing with other systems 50
  51. 51. Application Technical Assessment• Clarity of source code (understandable?)• Documentation (consistency, quality)• Data (data model?, level of duplication)• Performance (adequate, poor)• Programming Language (modern/obsolete)• Level of Configuration Management (complete, partial, none)• Test Data ( data & regression test availability)• Personnel Skills (availability?) 51
  52. 52. Legacy System Layers • A legacy system may be viewed as a set of layers • Each layer depends on and interfaces with the layer below • If interfaces are “clean” then “in theory” you should be able to make changes within a layer without affecting other layers. Rare in practice! Business processes Application software Support software Hardware 52
  53. 53. Summary• Legacy system: an “old system” still providing essential business services. – Encompass business processes, application software, support software and system hardware. – May be a collection of applications and shared data using files or obsolete database management system• Assess business value and quality of a legacy system hardware/software before decision to replace, transform or maintain the system. – Business value of a system is an assessment of the effectiveness of the system in supporting business goals. – System Quality is determined by business processes, application software and hardware and support software. 53
  54. 54. A Software Process is A structured set of activities required to develop a software system 54
  55. 55. Ad hoc Software Development• Developing software without planning for each phase, and without specifying tasks, deliverables, or time constraints.• Relies entirely on the skills and experience of the individual staff for performing the work.• The software process is constantly changed or modified as the work progresses. 55
  56. 56. Software Process ModelA Software process Model which is“an abstract representation of a process. It presents a description of a process from some particular perspective.”It provides guidelines to organize how software process activities should be performed and in what order. 56
  57. 57. The Capability Maturity Model• What is the Capability Maturity Model (CMM)? – The application of process management and quality improvement concepts to software development and maintenance. – A guide for evolving toward a culture of engineering excellence. – A model for organizational improvement. 57
  58. 58. Capability Maturity Model• Focuses on practices that are under control of the software group• Presents a minimum set of recommended practices that have been shown to enhance a software development and maintenance capability – It defines the expectation (the “what”) – Without overly constraining the implementation (the “how”) 58
  59. 59. Why We Chose CMM• CMM today serves as a “seal of approval” in software development• CMM helped guide us towards standard, repeatable processes – reduced learning time on how to get things done• Standard practices mean time savings to our team - everyone knows what to expect and what to deliver• Our quality activities became more aligned within the project rather than thought of as a separate event• We rely on our processes and our people together, not just one or the other• Ideas in CMM creates an environment of improvement – if you don’t like things one way, make it better! 59
  60. 60. Stages of Process Maturity Level Focus Process Areas Quality Continuous Organizational Innovation and Deployment 5 Optimizing Productivity Process Causal Analysis and Resolution Improvement4 Quantitatively Quantitative Organizational Process Performance Managed Management Quantitative Project Management Requirements Development Technical Solution Product Integration Verification Validation3 Defined Process Organizational Process Focus Standardization Organizational Process Definition Organizational Training Integrated Project Mgmt (with IPPD extras) Risk Management Decision Analysis and Resolution Integrated Teaming (IPPD only) Org. Environment for Integration (IPPD only) Integrated Supplier Management (SS only) Requirements Management Basic Project Planning Project Monitoring and Control2 Managed Project Supplier Agreement Management Management Measurement and Analysis Process and Product Quality Assurance Configuration Management Risk 1 Initial Rework 60
  61. 61. Level 1: the “Initial” LevelSuccess depends on heroesGood performance is possible - but• Requirements often misunderstood, uncontrolled• Schedules and budgets frequently missed• Progress not measured• Product content not tracked or controlled• Engineering activities nonstandard, inconsistent• Teams not coordinated, not trained• Defects proliferate 61
  62. 62. CMMI Level 2: “Managed” 7 Process AreasCLARIFY REQUIREMENTS Baseline the product requirements – Requirements Management (REQM)DOCUMENT PLANS Estimate project parameters, Project Planning (PP) Develop plans and processesTRACK PROGRESS Measure actual progress to enable – Project Monitoring timely corrective action and Control (PMC) Measure for mgmt. info needs – Measurement & Analysis (M&A) Verify adherence of processes – Process & Product and products to requirements Quality Assurance (PPQA)CONTROL PRODUCTS Identify and control products, – Configuration changes, problem reports Management (CM) Select qualified suppliers / vendors; – Supplier Agreement manage their activities Management (SAM) 62
  63. 63. What Happens During Level 2 • Processes become easier to digest and understand • Managers and team members spend less time explaining how things are done and more time doing • Projects are better estimated, better planned, and more flexible • Quality is integrated into the project • Costs may go up initially, but do go down over time • And yes, there may be more documentation and paper 63
  64. 64. CMMI Level 3: “Defined” 11 Process Areas*ENGINEER THE PRODUCT• Clarify customer requirements• Solve design requirements; develop – Requirements Definition (RD) implementation processes – Technical Solution (TS)• Assemble product components, deliver• Ensure products meet requirements• Ensure products fulfill intended use – Product Integration (PI)• Analyze decisions systematically – Verification (Ver) – Validation (Val)• Follow integrated, defined processes – Decision Analysis• Identify and control potential problems & Resolution (DAR)MANAGE THE PROCESSES• Establish org. responsibility for PI – Integrated Project Mgmt (IPM)• Define the org’s best practices – Risk Management (RSKM)• Develop skills and knowledgePROVIDE ORG. INFRASTRUCTURE – Org. Process Focus (OPF) – Org. Process Definition (OPD) – Org. Training (OT) 64
  65. 65. What Happens During Level 3• Process Improvement becomes the standard – Cross- Functional teams look for ways to “short-cut” the system• Solutions go from being “coded” to being “engineered”• Quality gates appear throughout the project effort with the entire team involved in the process, reducing rework• Risks are managed and don’t take the team by surprise 65
  66. 66. CMMI Level 4: “Quantitatively Managed” 2 Process AreasMANAGE PROJECTS QUANTITATIVELY • Statistically manage the project’s – Quantitative Project Management processes and sub-processes (QPM)MANAGE THE ORGANIZATION QUANTITATIVELY • Understand process performance; – Organizational quantitatively manage Process Performance (OPP) the organization’s projects 66
  67. 67. CMMI Level 5: “Optimizing” 2 Process AreasOPTIMIZE PERFORMANCE • Identify and eliminate – Causal Analysis the cause of defects early and Resolution (CAR)ADOPT IMPROVEMENTS • Identify and deploy new tools and process – Organizational Innovation improvements to meet needs and business and Deployment (OID) objectives 67
  68. 68. The CMM Maturity LevelsMaturity Level 1Maturity Level 2 ~Maturity Level 3 ~ ~ ~Maturity Level 4 ~ ~ ~ ~ ~ ~Maturity Level 5 ~ ~ ~ ~ ~ ~ 68
  69. 69. Proving Maturity Levels• Five characteristics must be demonstrated in each practice to be assessed in that maturity level practice areas: – Commitment to Perform – Policies, procedures, and resources to perform the work – Ability to Perform – Personnel, tools, and templates in place – Activities Performed – Documentation and interviews demonstrating that policies are implemented – Measurement and Analysis – Metrics and other tools used to evaluate effectiveness of processes – Verifying Implementation – Independent review and evaluation of the processes• Maturity levels are proven through documentation (policies, procedures, templates) and interviews of staff (to prove institutionalization). 69
  70. 70. Implementation Best Practices• Be Realistic – Some processes will be more ready than others.• Be Flexible – Allowing tailoring is key to adoption.• Be Open – The key is to learn how to do things better, not how to “comply”.• Be Patient – It does not happen overnight. 70
  71. 71. Classifications of SDLC Model SDLC Model Sequential Progressive Iterative V Model Waterfall 71
  72. 72. SW Process Models• Waterfall model• Evolutionary or Propgressive models• Component-based development model• Iterative Model 72
  73. 73. The Waterfall Model• Oldest model, it’s been around since 1970.• Called “Linear Sequential Model”.• Most widely used model for SW engineering• Documentation is produced at each stage. 73
  74. 74. Phases1. Requirements analysis and definition2. System and software design3. Implementation and unit testing4. Integration and system testing5. Operation and maintenance 74
  75. 75. Waterfall model diagram 75
  76. 76. Disadvantages• Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements.• Only appropriate when the requirements are well- understood and changes will be fairly limited during the design process.• The waterfall model is mostly used for large systems engineering projects. 76
  77. 77. Evolutionary Models 77
  78. 78. The Exploratory Model Objective is to work with customers and evolve a final system from an initial outline specification. Should start with well-understood requirements and add new features as proposed by the customer. 78
  79. 79. The Exploratory Model Concurr ent activities Initial Specification version Outline Intermedia te description Development versions Final Valida tion version 79
  80. 80. The Exploratory Model• Problems – Lack of process visibility; – Systems are often poorly structured;• Applicability – For small or medium-size interactive systems; – For parts of large systems (e.g. the user interface); – For short-lifetime systems. 80
  81. 81. The Prototyping ModelWhen a customer defines a set of general objectives for a software but does not identify detailed input, processing, or output requirement.It consists of the iterating phases: 1. Requirements gathering 2. Design and build SW prototype 3. Evaluate prototype with customer 4. Refine requirements 81
  82. 82. The Prototyping Model 82
  83. 83. The Prototyping Model• Advantages – Users get a feel for the actual system – Developers get to build something immediately – Specifications can be developed incrementally• Disadvantages – The developer may make implementation compromises in order to get a prototype working quickly. – The process in not visible (few documents that reflect every version of the system) – Systems poorly structured 83
  84. 84. Component Based SoftwareEngineering (CBSE)• Based on systematic reuse where systems are integrated from existing components.• Process stages – Component analysis; – Requirements modification; – System design with reuse; – Development and integration.• This approach is becoming increasingly used as component standards have emerged. 84
  85. 85. Component Based SoftwareEngineering (CBSE) Requirements Component Requirements System design specification analy sis modification with reuse Development Sy stem and integ ration validation 85
  86. 86. Component Based SoftwareEngineering (CBSE)• Advantages: – Reduce amount of software to be developed – Reduce costs and risks – Faster delivery• Disadvantages: – Requirements compromises, system does not meet real needs of users – Limited features 86
  87. 87. Iterative Models 87
  88. 88. The Incremental ModelRather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality.User requirements are prioritised and the highest priority requirements are included in early increments.Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve. 88
  89. 89. The Incremental Model Define outline Assign requirements Design sy stem requirements to increments architectur e Develop sy stem Valida te Integ rate Validate increment increment increment sy stem Final sy stem Sy stem incomplete 89
  90. 90. The Incremental ModelAdvantages:• Customer value can be delivered with each increment so system functionality is available earlier.• Early increments act as a prototype to help elicit requirements for later increments.• Lower risk of overall project failure.• The highest priority system services tend to receive the most testing. 90
  91. 91. The Incremental ModelDisadvantages:• Increments should be relatively small (20,000 lines of code)• Can be difficult to map the customer’s requirements onto increments of the right size• Hard to identify common functions 91
  92. 92. The Spiral Model• Defined by Barry Boehm in his 1988 article A Spiral Model of Software Development and Enhancement.• Process is represented as a spiral rather than as a sequence of activities with backtracking.• Each loop in the spiral represents a phase in the process.• Suitable for large, expensive and complicated projects 92
  93. 93. The Spiral Model Deter mine objecti ves, Evalua te alterna tives, alterna tives and identify, resolv e risks constr aints Risk anal ysis Risk anal ysis Risk Oper a- anal ysis Pr ototype 3 tional Prototype 2 protoype Risk REVIEW anal ysis Proto- type 1 Requir ements plan Simula tions , models , benchmar ks Life-cy cle plan Concept of Oper a tion S/W requir ements Product design Detailed Requir ement design De velopment plan valida tion Code Unit test Integ ra tion Design V&V Integ ra tion and test plan Plan ne xt phase test Acceptance 93 Service test De velop , verify ne xt-le vel pr oduct
  94. 94. The Spiral Model• Objective setting – Specific objectives for the phase are identified.• Risk assessment and reduction – Risks are assessed and activities put in place to reduce the key risks.• Development and validation – A development model for the system is chosen which can be any of the generic models.• Planning – The project is reviewed and the next phase of the spiral is planned. 94
  95. 95. The Spiral Model• Risk driven process model – Different risk patterns can lead to choosing different process models• What is a risk? – Situations or possible events that may cause a project to fail to meet its goal. – Example risks: • Experienced staff leave the project • Hardware which is essential for the system will not be delivered on schedule – (more about risks in Chapter 3) 95
  96. 96. The Spiral ModelAdvantages:• Risks are explicitly assessed and resolved throughout the process.• Software engineers can start working on the project earlier rather than wading through a lengthy early design process. 96
  97. 97. The Spiral ModelDisadvantages:• Requires highly skilled people in risk analysis and planning• Requires more time, and is more expensive• Estimates of budget and time are harder to judge at the beginning of the project since the requirements evolve through the process 97