The context diagram represents the entire system under investigation. It should be drawn first, and used to clarify and agree the scope of the investigation. The system under investigation is represented as a single process, connected to external entities by data flows and resource flows.The context diagram clearly shows the interfaces between the system under investigation and the external entities with which it communicates. Therefore, whilst it is often conceptually trivial, a context diagram serves to focus attention on the system boundary and can help in clarifying the precise scope of the analysis.