Why are requirements important?
Requirements are of vital importance for every systems engineering process: Stakeholders have certain goals, and they hope to achieve these goals with the help of a (planned) system. To be able to do this, the system has to possess certain characteristics and features. The problem: Goals are too broad to derive specific system characteristics from these goals, and this is where requirements come in. Requirements concretize goals by describing in detail what features and characteristics a system must offer in order to satisfy the stakeholders.
Completeness, soundness and depth of detail are key when it comes to supporting other departments and disciplines partaking in the development process. In addition, disciplines such as systems architecture, design, implementation and testing are highly dependent from the requirements elicited as well as from their quality. The relevance of the requirements even goes beyond develpoment; activities like risk analysis, effort estimation maintenance and decomissioning are also based on the system requirements.
What is a requirements diagram?
The difference between textual elicitation of requirements and requirements diagrams is that diagrams allow for a significantly more structured and comprehensible way of illustrating requirements. Instead of compiling long and arduous lists, requirements engineers are able to model all relevant requirements in a way that is easily accessible for all project contributors. What is more, not only requirements are part of a requirements diagram, but also relationships to other elements. The example above shows a requirements diagram for an irrigation plant.