The document discusses several software development life cycle models: - The phased model segments development into phases like analysis, design, implementation, testing and maintenance. - The cost model views the life cycle in terms of costs incurred in each phase and modifying previous work. - Prototyping involves building initial versions to explore technical issues and illustrate requirements for the customer. - Successive versions refines an initial product skeleton through multiple iterations. Planning the development process involves choosing a life cycle model and defining documents, milestones and reviews. This provides structure and visibility needed for control and quality.