Non-Functional Requirements

In the software market place, in which functionally equivalent products compete for the same customer, Non Functional Requirements (NFRs) become more important in distinguishing between the competing products. However, in practice, NFRs receive little attention relative to Functional Requirements (FRs). This is mainly because of the nature of NFRs which poses a challenge when taking the choice of treating them earlier in the software development. NFRs are subjective, relative and cross-cutting. Furthermore, NFRs can often interact, in the sense that attempts to achieve one NFR can help or hinder the achievement of other NFRs at particular software functionality. Such an interaction creates an extensive network of interdependencies and tradeoffs among NFRs which is not easy to trace or estimate. This book contributes towards achieving the goal of managing the attainable scope and the changes of NFRs. It proposes and empirically evaluates a formal and quantitative approach to modeling and assessing NFRs. The applicability of this work should be especially useful to researchers in the requirements engineering field and the participators in software industry.