Spiral Model

The key characteristic of a Spiral model is risk management at regular stages in the development cycle. In 1988, Barry Boehm published a formal software system development "spiral model", which combines some key aspect of the waterfall model and rapid prototypingmethodologies, but provided emphasis in a key area many felt had been neglected by other methodologies: deliberate iterative risk analysis, particularly suited to large-scale complex systems.

The Spiral is visualized as a process passing through some number of iterations, with the four quadrant diagram representative of the following activities:

1. formulate plans to: identify software targets, selected to implement the program, clarify the project development restrictions;
2. Risk analysis: an analytical assessment of selected programs, to consider how to identify and eliminate risk;
3. the implementation of the project: the implementation of software development and verification;

Risk-driven spiral model, emphasizing the conditions of options and constraints in order to support software reuse, software quality can help as a special goal of integration into the product development. However, the spiral model has some restrictive conditions, as follows:

1. spiral model emphasize risk analysis, but require customers to accept and believe that much of this analysis, and make the relevant response is not easy, therefore, this model is often adapted to large-scale internal software development.
2. If the implementation of risk analysis will greatly affect the profits of the project, then risk analysis is meaningless, therefore, spiral model is only suitable for large-scale software projects.
3. Good software developers should look for possible risks, an accurate analysis of risk, otherwise it will lead to greater risk.

First stage is to determine the stage of the goal of accomplishing these objectives, options and constraints, and then from the perspective of risk analysis program, development strategy, and strive to remove all potential risks, and sometimes necessary to achieve through the construction of the prototype. If some risk can not be ruled out, the program to end immediately, or else start the development of the next steps. Finally, evaluation results of the stage, and the design of the next phase.