Software Lifecycles

Waterfall

The least flexible and most obsolete of the life cycle models. It is only well suited to projects that have low risk in the areas of user interface and performance requirements, but high risk in budget and schedule predictability and control. It is not used very much any more.

Spiral

The spiral model is the most generic of the models. Most life cycle models can be derived as special cases of the spiral model. The spiral uses a risk management approach to software development. Some advantages of the spiral model are:

• defers elaboration of low risk software elements
• incorporates prototyping as a risk reduction strategy
• gives an early focus to reusable software
• accommodates life-cycle evolution, growth, and requirement changes
• incorporates software quality objectives into the product
• focus on early error detection and design flaws
• sets completion criteria for each project activity to answer the question: "How much is enough?"
• uses identical approaches for development and maintenance
• can be used for hardware-software system development

Chaos

The chaos model notes that the phases of the life cycle apply to all levels of projects, from the whole project to individual lines of code.

Projects can be thought of being built in pieces. Nobody writes tens of thousands of lines of code in one sitting. They write small pieces, one line at a time, verifying that the small pieces work. The projects are built up from there. The behavior of a complex system emerges from the combined behavior of the smaller building blocks.

Rapid prototyping Cycle