Context diagrams

A context diagram is a graphical method of representing a system using a single process together with inputs and outputs (external entities). There are only three symbols in a context diagram: the process, the data flow and the external entity (see Table 3.3). 

The external entities are linked to the process by data flow arrows. A context diagram is often the starting point of a data flow diagram. 

The context diagram in Figure 3.5 shows the method for finding a book in the library. It clearly shows the flow of data in the system.