Software process life cyclesSoftware and entropyPlanning for changeA software process requires resources…A software life cycle is a processWaterfall model of software processWhy would corporate manager types like the waterfall life cycle model?Testing in the waterfall modelMore drawbacks of the waterfall modelPrototypingV modelBalzer’s transformational modelPhased developmentIterative and incremental processSlide 15Rational Unified Process (RUP)Agile MethodsHow do traditional stages iterate?Slide 19Inception Elaboration …… Construction TransitionUP phases are iterative & incrementalUP artifactsSlide 24Slide 25What does diagram imply about UP?Slide 27Software process life cyclesCSE 432: Object-Oriented Software EngineeringSoftware and entropyA virtue of software: relatively easy to changeOtherwise it might as well be hardwareNevertheless, the more complex a software system gets, the harder it is to change--why?Larger software systems are harder to understandThe more changes get introduced into a system, the more it tends toward entropy I.e., its internal order breaks downMultimedia: http://www.cse.lehigh.edu/~cimel/prototype.htmlPlanning for changeHow can good comments facilitate and reduce the cost of software maintenance?Hint: think about invariants, things that don’t change.Comments describe meaning of codeAssuming programmers maintain comments when they change the code!How can modularity help manage change?Modules help to isolate and localize changeA software process requires resources…A software life cycle is a processA process involves activities, constraints and resources that produce an intended output.Each process activity, e.g., design, must have entry and exit criteria—why?A process uses resources, subject to constraints (e.g., a schedule or a budget)A process is organized in some order or sequence, structuring activities as a whole A process has a set of guiding principles or criteria that explain the goals of each activityWaterfall model of software processMultimedia: stages in the processCascades from one stage down to the next, in stately, lockstep, glorious order.Gravity only allows the waterfall to go downstream;it’s very hard to swim upstreamDepartment of Defense contracts prescribed this model for software deliverables for many years, in DOD Standard 2167-A.Why would corporate manager types like the waterfall life cycle model?Minimizes change, maximizes predictabilityCosts and risks are more predictableEach stage has milestones and deliverables: project managers can use to gauge how close project is to completionSets up division of labor: many software shops associate different people with different stages:Systems analyst does analysis, Architect does design, Programmers code, Testers validate, etc.Testing in the waterfall modelLet’s look at more Pfleeger’s version of waterfall modelMany waterfall models show 5 stages—why more here?What’s the difference between unit and system testing?Between system and acceptance testing?What kind of arrows are missing?Is this diagram a more realistic picture?Is this view of the process a good idea?The reality is that not only does software change, but change happens during the processRealistic models are not strictly linear, but allow for cyclesBear in mind, however, that more cycles mean more costsMore drawbacks of the waterfall modelOffers no insight into how how does each activity transform one artifacts (documents) of one stage into anotherFor example, requirements specification design documents?Fails to treat software a problem-solving processUnlike hardware, software development is not a manufacturing but a creative processManufacturing processes really can be linear sequences, but creative processes usually involve back-and-forth activities such as revisionsSoftware development involves a lot of communication between various human stakeholdersNevertheless, more complex models often embellish the waterfall, incorporating feedback loops and additional activitiesPrototypingThis model adds prototyping as sub-processA prototype is a partially developed product that enables customers and developers to examine some aspect of a proposed system and decide if it is suitable for a finished productWhy add prototypes to the life cycle?Used to explore the risky aspects of the system:Risk of developing the “wrong” system (what customer doesn’t want), can be a user interface without functionalityOther technical risks – e.g. performance, using a new technology, alternative algorithms, etc.Prototype may be thrown away or evolve into productV modelDeveloped by the German Ministry of DefenseWhat does this model highlight?Unit and system testing verify the program design, ensuring that parts and whole work correctlyAcceptance testing, conducted by the customer rather than developers, validates the requirements, tying each system function meets a particular requirement in the specificationHow does this model account for cycles?If problems are found during verification or validation, then re-execute left side of V to make fixes and improvementsWhile the waterfall emphasizes documents and artifacts, the V model emphasizes activities and correctnessBalzer’s transformational modelTries to reduce error in most software processes by:eliminating development steps, emphasizing formal specifications, and using automated support to facilitate transformations from specification to deliverable systemHitch: the need for a formal specification precise enough for automated transformationsWe’ll see that even semi-formal specifications can help with other software life cyclesPhased developmentNowadays, customers are less willing to wait years for a software system to be readySo it’s necessary to reduce the cycle time of software productsIn 1996, 80% of HP’s revenues derived from products developed in previous two yearsHow is this accelerated cycle time made possible?Phased development reduces cycle timeDesign a system so it can be delivered in pieces, letting users have some functionality while the rest is under developmentSo there are usually two or more systems in parallel: The operational or production system in use by customers The development system which will
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