Software ProcessesObjectivesTopics coveredThe software processGeneric software process modelsWaterfall modelWaterfall model phasesWaterfall model problemsEvolutionary developmentSlide 10Slide 11Component-based software engineeringReuse-oriented developmentProcess iterationIncremental deliveryIncremental developmentIncremental development advantagesExtreme programmingSpiral developmentSpiral model of the software processSpiral model sectorsProcess activitiesSoftware specificationThe requirements engineering processSoftware design and implementationDesign process activitiesThe software design processStructured methodsProgramming and debuggingThe debugging processSoftware validationThe testing processTesting stagesTesting phasesSoftware evolutionSystem evolutionThe Rational Unified ProcessRUP phase modelSlide 39RUP phasesRUP good practiceStatic workflowsComputer-aided software engineeringCase technologyCASE classificationFunctional tool classificationActivity-based tool classificationCASE integrationTools, workbenches, environmentsKey pointsSlide 51©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 1Software Processes©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 2ObjectivesTo introduce software process modelsTo describe three generic process models and when they may be usedTo describe outline process models for requirements engineering, software development, testing and evolutionTo explain the Rational Unified Process modelTo introduce CASE technology to support software process activities©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 3Topics coveredSoftware process modelsProcess iterationProcess activitiesThe Rational Unified ProcessComputer-aided software engineering©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 4The software processA structured set of activities required to develop a software system•Specification;•Design and implementation;•Validation;•Evolution.A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective.©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 5Generic software process modelsThe waterfall model•Separate and distinct phases of specification and development.Evolutionary development•Specification, development and validation are interleaved.Component-based software engineering•The system is assembled from existing components.There are many variants of these models e.g. formal development where a waterfall-like process is used but the specification is a formal specification that is refined through several stages to an implementable design.©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 6Waterfall modelRequirementsdefinitionSystem andsoftware designImplementationand unit testingIntegration andsystem testingOperation andmaintenance©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 7Waterfall model phasesRequirements analysis and definitionSystem and software designImplementation and unit testingIntegration and system testingOperation and maintenanceThe main drawback of the waterfall model is the difficulty of accommodating change after the process is underway. One phase has to be complete before moving onto the next phase.©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 8Waterfall model problemsInflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements.Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process. Few business systems have stable requirements.The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites.©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 9Evolutionary developmentExploratory development •Objective is to work with customers and to evolve a final system from an initial outline specification. Should start with well-understood requirements and add new features as proposed by the customer.Throw-away prototyping•Objective is to understand the system requirements. Should start with poorly understood requirements to clarify what is really needed.©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 10Evolutionary developmentConcurrentactivitiesValidationFinalversionDevelopmentIntermediateversionsSpecificationInitialversionOutlinedescription©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 11Evolutionary developmentProblems•Lack of process visibility;•Systems are often poorly structured;•Special skills (e.g. in languages for rapid prototyping) may be required.Applicability•For small or medium-size interactive systems;•For parts of large systems (e.g. the user interface);•For short-lifetime systems.©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 12Component-based software engineeringBased on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-the-shelf) systems.Process stages•Component analysis;•Requirements modification;•System design with reuse;•Development and integration.This approach is becoming increasingly used as component standards have emerged.©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 13Reuse-oriented developmentRequirementsspecificationComponentanalysisDevelopmentand integrationSystem designwith reuseRequirementsmodificationSystemvalidation©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 14Process iterationSystem requirements ALWAYS evolve in the course of a project so process iteration where earlier stages are reworked is always part of the process for large systems.Iteration can be applied to any of the generic process models.Two (related) approaches•Incremental delivery;•Spiral development.©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 4 Slide 15Incremental