Requirements are normally classified as one of two main types: functional requirements or non-functional requirements. Although this distinction is normally made among software engineers and found in the literature, what is important is to make sure that all the requirements for a software system are identified. Therefore, such classification of the types of requirements is used to assist software developers during the identification of those requirements. Figure 1 shows a classification for the various types of requirements. Figure 1: Classification of types of requirements What is requirement? and difference between functional and non-functional requirements? And why the quality requirement is important for the system