Software PrototypingUses of System PrototypesPrototyping BenefitsPrototyping ObjectivesApproaches to PrototypingEvolutionary PrototypingSlide 7Evolutionary Prototyping ProblemsThrow-away PrototypingThrow-away Prototyping ProcessPrototypes as SpecificationsIncremental DevelopmentIncremental Development ProcessPrototyping TechniquesVery High-level LanguagesPrototyping LanguagesSmalltalkFourth-generation Languages4GLsPrototyping with ReuseReusable Component CompositionVisual ProgrammingVisual Programming with ReuseProblems with Visual DevelopmentUser Interface Prototyping©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 1Software PrototypingAnimating and demonstrating system requirements©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 2Uses of System PrototypesThe principal use is to help customers and developers understand the requirements for the system.The prototype may be used for user training before a final system is delivered.The prototype may be used for back-to-back testing.©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 3Prototyping BenefitsMisunderstandings between software users and developers are exposed.Missing services may be detected.Confusing services may be identified.A working system is available early in the process.The prototype may serve as a basis for deriving a system specification.©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 4Prototyping ObjectivesThe objective of evolutionary prototyping is to deliver a working system to end-users. The development starts with those requirements which are best understood.The objective of throw-away prototyping is to validate or derive the system requirements. The prototyping process starts with those requirements which are poorly understood©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 5Approaches to PrototypingEvolutionaryprototypingThrow-awayPrototypingDeliveredsystemExecutable Prototype +System SpecificationOutlineRequirements©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 6Evolutionary PrototypingMust be used for systems where the specification cannot be developed in advance e.g., AI systems and user interface systemsBased on techniques which allow rapid system iterations.Verification is impossible as there is no specification. Validation means demonstrating the adequacy of the system.©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 7Evolutionary PrototypingBuild prototypesystemDevelop abstractspecificationUse prototypesystemDeliversystemSystemadequate?YESN©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 8Evolutionary Prototyping ProblemsExisting management processes assume a waterfall model of development.Continual change tends to corrupt system structure so long-term maintenance is expensive.Specialist skills are required which may not be available in all development teams.Organizations must accept that the lifetime of systems developed this way will inevitably be short.©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 9Throw-away PrototypingUsed to reduce requirements risk.The prototype is developed from an initial specification, delivered for experiment then discarded.The throw-away prototype should NOT be considered as a final system:–Some system characteristics may have been left out.–There is no specification for long-term maintenance.–The system will be poorly structured and difficult to maintain.©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 10Throw-away Prototyping ProcessOutlinerequirementsDevelopprototypeEvaluateprototypeSpecifysystemDevelopsoftwareValidatesystemDeliveredsoftwaresystemReusablecomponents©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 11Prototypes as SpecificationsSome parts of the requirements (e.g., safety-critical functions) may be impossible to prototype and so don’t appear in the specification.An implementation has no legal standing as a contract.Non-functional requirements cannot be adequately tested in a system prototype.©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 12Incremental DevelopmentSystem is developed and delivered in increments after establishing an overall architecture.Users may experiment with delivered increments while others are being developed. Intended to combine some of the advantages of prototyping but with a more manageable process and better system structure.©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 13Incremental Development ProcessValidateincrementBuild systemincrementSpecify systemincrementDesign systemarchitectureDefine systemdeliverablesSystemcomplete?IntegrateincrementValidatesystemDeliver finalsystemYESNO©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 14Prototyping TechniquesVery high-level languagesApplication generators and 4GLsComposition of reusable components©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 8 Slide 15Very High-level LanguagesLanguages which include powerful data management facilities.Need a large run-time
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