Page 115 - DCAP304_DCAP515_SOFTWARE_PROJECT_MANAGEMENT

Unit 5: Project Approach

Spiral Model Notes
Figure 5.3: Spiral Model

DETERMINE GOALS, EVALUATE ALTERNATIVES
ALTERNATIVES, AND RISKS
CONSTRAINTS Constraints 4 Risk analysis 4

Alternatives 4 Constraints 3 Risk analysis 3
Alternatives 3 Constraints 2 Risk analysis 2

Alternatives 2

Budget 4 Budget Budget Alternatives 1 Risk analysis 1 Proto- Proto- Proto-
type
Prototype type
type
Constraints
3 2 Budget 1 1 2 3 4
1
start
requirements
Requirements, Concept of
life-cycle plan operation Software Software Detailed
design design
Validated Code
requirements
Development
plan
Validated,
Integration
verified design
and test plan
Unit test
System
Implementation Acceptance test
plan test
PLAN DEVELOP AND TEST
MSE 555: Introduction - 29
Copyright 2003
The essential concept of the Spiral Model is “to minimize risks by the repeated use of prototypes
[emphasis added] and other means. Unlike other models, at every stage risk analysis is
performed. The Spiral Model works by building progressively more complete versions of the
software by starting at the center of the spiral and working outwards. With each loop of the
spiral, the customer evaluates the work and suggestions are made for its modification.
Additionally, with each loop of the spiral, a risk analysis is performed which results in a ‘go/no-
go’ decision. If the risks are determined to be too great then the project is terminated” [Frankovich
1998]. Thus, the Spiral Model addresses the problem of requirements engineering through
development of prototypes, and it addresses the need for risk management by performing risk
analysis at each step of the life cycle.
Did u know? What are prototypes?
A prototype is an early sample or model built to test a concept or process or to act as a
thing to be replicated or learned from.

5.3.4 Prototype Model

A prototype model is beneficial when the customer requirements are dynamic and keep on changing
with time and the developer is unsure about the software adaptability with the system and the
operating system. Thus in a prototype model, a working prototype is built with the available set of
requirements such that it has limited functionalities, low reliability and performance.

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