Project life cycles
Waterfall, V-model, spiral, iterative and incremental: how each sequences its activities, its strengths and limits, the context where each fits, and the contrast between predictive and adaptive approaches.
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Software life cycle: what is it?
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The sequence of major activities a piece of software goes through, from stating the need to its retirement, via building and maintenance.
Choosing a life-cycle model means choosing the order of activities and when the client gives feedback, not how good each activity is.
In the V-model, which test checks the detailed design, that is each component taken on its own?
- Unit tests
- Integration tests, which assemble the components
- Validation tests of the whole system
- Acceptance by the client
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Unit tests
Each design level has its own test level: detailed design and unit tests, general design and integration tests, specifications and validation tests, need and acceptance.
An … redoes and improves what already exists; an … adds one more usable piece to the product.
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An iteration redoes and improves what already exists; an increment adds one more usable piece to the product.
They combine: each short cycle adds an increment and improves the previous ones based on feedback.
Waterfall model: what is it?
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A model where the phases follow one another in a single sequence, each finished and validated before the next, with testing coming only after coding; going back is rare and costly.
It suits a stable, well-known need. Its flaw: the client only sees the product at the end, when a misunderstanding costs the most.
The need is vague, the client is available and the market is moving. The team works in waterfall and delivers a stale product after 18 months. Which life cycle should it adopt?
- A V-model, to write test plans as early as the design
- Waterfall, with a longer specification phase
- A V-model, with more frequent design reviews
- An iterative and incremental cycle, with a usable version at regular intervals
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An iterative and incremental cycle, with a usable version at regular intervals
The cause is no client feedback before the end. A longer specification does not make the need more stable; regular versions let the team correct course early.