Abstract
With the growing awareness of the effects of requirements in software processes, requirements engineering is increasingly becoming an area of focus in software engineering research. A vast number of studies assert that failure in understanding and classifying requirements are the main causes of exceeding costs and allocated time, which in turn results in project failure. Successful software systems development requires consistent and classified requirements. Requirements classification represents an early but critical phase in the requirements analysis stage. While the literature draws a distinction between different types of requirements, in practice it is not always easy to identify such differences. This paper provides an overview of requirements classification, presents some of the existing research studies on requirements classification, and discusses their limitations to yield suggestions for improvement.