Requirements Types

For ease of use, we have found it convenient to think of requirements as belonging to a type.

Functional requirements are the fundamental or essential subject matter of the product. They describe what the product has to do or what processing actions it is to take.

Nonfunctional requirements are the properties that the functions must have, such as performance and usability. Do not be deterred by the unfortunate name (we use it because it is the most common way of referring to these types of requirements)these requirements are as important as the functional requirements for the product's success.

Project constraints are restrictions on the product due to the budget or the time available to build the product.

Design constraints impose restrictions on how the product must be designed. For example, it might have to be implemented in the hand-held device being given to major customers, or it might have to use the existing servers and desktop computers, or any other hardware, software, or business practice.

Project drivers are the business-related forces. For example, the purpose of the project is a project driver, as are all of the stakeholderseach for different reasons.

Project issuesdefine the conditions under which the project will be done. Our reason for including them as part of the requirements is to present a coherent picture of all factors that contribute to the success or failure of the project and to illustrate how managers can use requirements as input when managing a project.