User Requirements (functional and functional requirements)

User Requirements (functional and functional requirements)

The requirements for a system are the descriptions of the services provided by the system and its operational constraints. These requirements reflect the needs of customers for a system that helps solve some problem such as controlling a device, placing an order or finding information. The process of finding out, analyzing, documenting and checking these services and constraints is called requirements engineering (RE).
Some of the problems that arise during the requirements engineering process are a result of failing to make a clear separation between these different levels of description. I distinguish between them by using the term user requirements to mean the high-level abstract Requirements and system requirements to mean the detailed description of what the system should do. User requirements and system requirements may be defined as follows:
1. User requirements are statements, in a natural language plus diagrams, of what services the system is expected to provide and the constraints under which it must operate.
2. System requirements set out the system’s functions, services and operational constraints in detail. The system requirements document (sometimes called a functional specification) should be precise. It should define exactly what is to be implemented. It may be part of the contract between the system buyer and the software developers