Software Engineering Lec#7

Third. Boehm’s spiral model
A risk-driven software process framework (the spiral model) was proposed by Boehm (1988). This is shown in next figure. Rather than represent the software process as a sequence of activities with some backtracking from one activity to another, the process is represented as a spiral .Each loop in the spiral represents a phase of the software process. Thus, the deepest loop might be concerned with system feasibility, the next loop with requirements definition, the next loop with system design, and so on. The spiral model combines change avoidance with change tolerance. It assumes that changes are a result of project risks and includes explicit risk management activities to reduce these risks.
Each loop in the spiral is split into four sectors:
1. Objective setting: Specific objectives for some phase of the project are defined. Constraints on the process and the product are identified and a detailed management plan is drawn up. Project risks are identified. Alternative strategies, depending on these risks, may be planned.
2. Risk assessment and reduction: For each of the identified project risks, a detailed analysis is carried out. Steps are taken to reduce the risk. For example, if there is a risk that the requirements are inappropriate, a prototype system may be developed.
3. Development and validation: After risk evaluation, a development model for the system is chosen. For example, throwaway prototyping may be the best development