1Software Life CycleFawzi EmadChau-Wen TsengDepartment of Computer ScienceUniversity of Maryland, College ParkSoftware Life Cycle1. Problem specification2. Program design3. Algorithms and data structures4. Coding and debugging5. Testing and verification6. Documentation and support7. Maintenance2Program DesignGoalBreak software into integrated set of componentsthat work together to solve problem specificationProblemsMethods for decomposing problemHow to divide workWhat work to divideHow components work togetherDesign – How To Divide WorkDecomposing problemBreak large problem into many smaller problemsCannot solve large problems directlyDivide and conquer1. Break problem up into simpler sub-problems2. Repeat for each sub-problem3. Stop when sub-problem can be solved easily3Design – How To Divide WorkFunctional approachTreat problem as a collection of functionsTechniquesTop-down designSuccessively split problem into smaller problemsBottom-up designStart from small tasks and combineDesign – Decomposition ExampleTop-down design of banking simulator4Design – How To Divide WorkObject-oriented approachTreat problem as a collection of data objectsObjects Entities that exist that exist in problemContain dataPerform actions associated with dataDesign – Comparison ExampleBank simulationFunctional programmingArrivals, departures, transactionsObject-oriented programmingCustomers, lines, tellers, transactions5Design – Comparing ApproachesFunctional approachTreat problem as a collection of functionsFunctions perform actionsThink of functions as verbsObject-oriented approachTreat problem as a collection of data objectsObjects are entities that exist that exist in problemThink of objects as nounsDesign – Comparing ApproachesAdvantages to object-oriented approachHelps to abstract problemSimpler high-level viewHelps to encapsulate dataHides details of internals of objectsCentralizes and protects all accesses to dataSeems to scale better for larger projectsIn practiceTend to use a combination of all approaches6Design – ComponentsComponents must work together easilyEach component requiresInterfaceHow component is accessedPre-conditionsWhat conditions are true before invocationPost-conditionsWhat conditions are true after invocationDesign – Interface & ConditionsFunction positivePower()Calculate xnfor positive values of x & nInterfacepublic static float positivePower(float x, int n)Pre-conditionsx has positive floating point value > 0.0n has positive integer value ≥ 0Post-conditionsReturns xnif preconditions are metReturns –1.0 otherwise7Algorithms and Data StructuresGoalSelect algorithms and data structures to implement each componentProblemsFunctionalityProvides desired abilitiesEfficiencyProvides desired performanceCorrectnessProvides desired resultsAlgorithms and Data StructuresExampleImplement list as array or linked list8Coding and DebuggingGoalWrite actual code and ensure code worksProblemsChoosing programming languageFunctional designFortran, BASIC, Pascal, CObject-oriented designSmalltalk, C++, JavaUsing language featuresExceptions, streams, threadsTesting and VerificationGoalDemonstrate software correctly match specificationProblemProgram verificationFormal proof of correctnessDifficult / impossible for large programsEmpirical testingVerify using test casesUnit tests, integration tests, alpha / beta testsUsed in majority of cases in practice9Documentation and SupportGoalProvide information needed by users and technical maintenanceProblemsUser documentationHelp users understand how to use softwareTechnical documentationHelp coders understand how to modify, maintain softwareMaintenanceGoalKeep software working over timeProblemsFix errorsImprove featuresMeet changing specificationAdd new
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