Page 63 - DCAP405_SOFTWARE_ENGINEERING

Software Engineering

Notes
Figure 4.3: The Spiral Model

The risk-driven nature of the spiral model allows it to accommodate any mixture of a
specification-oriented, prototype-oriented, simulation-oriented, or some other type of approach.

Notes An important feature of the model is that each cycle of the spiral is completed by a
review that covers all the products developed during that cycle, including plans for the
next cycle.
The spiral model works for development as well as enhancement projects. In a typical application
of the spiral model, one might start with an extra round zero, in which the feasibility of the basic
project objectives is studied. These project objectives may or may not lead to a development/
enhancement project. Such high-level objectives include increasing the efficiency of code
generation of a compiler, producing a new full-screen text editor and developing an environment
for improving productivity. The alternatives considered in this round are also typically very
high-level, such as whether the organization should go for in-house development, or contract it
out, or buy an existing product. In round one, a concept of operation might be developed. The
objectives are stated more precisely and quantitatively and the cost and other constraints are
defined precisely. The risks here are typically whether or not the goals can be met within the
constraints. The plan for the next phase will be developed, which will involve defining separate
activities for the project. In round two, the top-level requirements are developed. In succeeding
rounds, the actual development may be done.

56 LOVELY PROFESSIONAL UNIVERSITY