Software Development Models

Read this summary of software development models and try to address the main features of each model. Note that this development approach might be categorized in a different way in other resources.

Waterfall Model

waterfall model

Deliverables − baselines
Document − driven process
"Big Bang" testing, "stubs", daily build and smoke test
"A Rational Design Process and How to Fake It"

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 a tool for requirements analysis. Need proper tools

2) Use to accommodate 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 are made.

Evolutionary Models (2)

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

− Alavi: prototyping vs. waterfall applied to an information system Prototyping: users more positive and more involved Waterfall: more robust and efficient data structures

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 are implemented, tested, and delivered according to different priorities and at different times.

Spiral Model

Includes every other model

Risk driven (vs. document driven or increment driven)
Radius of spiral represents cost accumulated so far

In requirements analysis, identify aspects that are uncertain

e.g., library:

checkout and checkin (inventory control) − relatively certain

card catalogue, user search − relatively uncertain

Software Factory

Most software organizations get strictly separated between initial development and later maintenance.

− No incentive to produce a system that can be easily maintained.

− No incentive to produce reusable components.

Project management vs. product management
Extend management responsibility to cover family of products rather than an individual product (product families)

Despite the rhetoric, CMM emphasizes control over flexibility and learning

Control orientation seeks to maintain predictable operations, minimize variation, and avoid surprises.
Learning orientation seeks to increase variation in order to explore opportunities.
Formal bureaucratic control undermines intrinsic motivation needed for creative and flexible responses to uncertainty.
Senge: humanistic values of caring and individual freedom are essential to building learning organizations.
Carroll: "In too many TQM programs, it is the difficult−to−implement portions of the program that are being finessed or ignored and the rhetoric that is being retained".

CS302: Software Engineering