An organization that wants to understand the performance of its software system projects needs to gather a lot of data about the requirements for and attributes of the delivered system, and the requirements and constraints for the projects. Exploiting these data to develop performance benchmarks and for estimating new projects needs consistent terminology and data definitions across all these activities.

The most important characteristic of the software that must be captured in support of these activities is a measure of its size. The COSMIC and IFPUG organizations1 offer ISO standard methods of measuring a size of the Functional User Requirements (FUR) for software, but have differing ideas on what to do about so-called ‘Non-Functional Requirements’ (NFR). Examples of software system requirements that are often cited as NFR are: response time, security, availability, portability, programming language, etc.

The topic of NFR is difficult because there are so many possible types of NFR (over 100 according to some authors) and only rather fuzzy definitions of what are NFR. The boundaries between ‘functional’ and ‘non-functional’ requirements are often not clear, with no agreed standard distinction. In addition, there are many types of project requirements and constraints, but again no agreement on the most important of these parameters that should be captured across the activities of performance measurement, benchmarking and estimating and their definitions.

As a first step to try to introduce some common understanding, the COSMIC and IFPUG organizations decided to collaborate to produce this standard Glossary of terms for NFR and for project requirements and constraints (PRC). The exercise has also helped the two organizations towards a better understanding of what exactly are NFR.

In addition to this Glossary, each organization also publishes its own standard which goes into further detail on these concepts and how to consider or how to measure non-functional requirements (COSMIC [1] or IFPUG [2], respectively).

We hope that the Glossary will be valuable in providing a common language to anyone involved in developing requirements for a software system project and/or who participates in the processes of contracting, developing or managing software projects, even if not specifically concerned with software measurement and its uses.

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  Chapter 1 is an introduction that presents the purpose of this document
• Chapter 2 gives the COSMIC and IFPUG definitions for FUR, for NFR and for PRC.
• Chapter 3 describes a classification scheme for NFR and for PRC to help the users of this Glossary to understand their scope, and to explain the reasons for the choice of which terms to include in the Glossary.
• Chapter 4 contains the Glossary of NFR terms and their definitions, (ISO wherever possible), the Glossary of PRC terms and some terms that were excluded from the Glossaries for particular reasons

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