Software Engineering презентация

Software Engineering

Waterfall Model

Evolutionary Model Prototyping − "Do it twice" to assess feasibility to verify requirements May only be a front end or executable specification Or develop system with less functionality or quality attributes 3 approaches: 1) Use prototyping as tool for requirements analysis. Need proper tools 2) Use to accomodate design uncertainty. Prototype evolves into final product Documentation may be sacrificed May be less robust Quality defects may cause problems later 3) Use to experiment with different proposed solutions before large investments made.

Evolutionary Model Drawbacks: Can be expensive to build Can develop a life of its own − turns out to be product itself Hard to change basic decisions made early Can be an excuse for poor programming practices Experimental Evaluation: Boehm: prototyping vs. waterfall Waterfall: addressed product and process control risks better Resulted in more robust product, easier to maintain Fewer problems in debugging and integration due to more thought−out design Prototyping: addressed user interfaces better

Incremental Model Functionality produced and delivered in small increments. Focus attention first on essential features and add functionality only if and when needed Systems tend to be leaner − fights overfunctionality syndrome May be hard to add features later Variant: Incremental implementation only Follow waterfall down to implementation During requirements analysis and system design Define useful subsets that can be delivered Define interfaces that allow adding later smoothly Different parts implemented, tested, and delivered according to different priorities and at different times.

Incremental Model

Incremental Model

Spiral Model Includes every other model Risk driven (vs. document driven or increment driven) Radius of spiral represents cost accumulated so far

Spiral Model

Spiral Model The planning task - to define resources, responsibilities, milestones and schedules. The goal determination task - to define the requirements and constraints for the product and define possible alternatives. The risk analysis task - to assess both technical and management risks. The engineering task - to design and implement one or more prototypes or samples of the application.

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