Traditionally a quality product is
defined in terms of its fitness of purpose that is, a quality
product does exactly what the user want it to do. For
Software products, the fitness of purpose is usually
interpreted in terms of satisfaction of the requirement laid
down in software requirement specification document. As
we have seen during Literature survey of software quality
that the modern view of quality associates a software
product with several quality factors such as Portability,
Usability, Reliability, Correctness, and Maintainability,
etc. Software Reliability, unlike many other quality
factors, Can be measured directly and estimated historical
and development data.