A Data Flow Diagram (DFD) is a diagram that divides an IS into processes (or functions) from the top down while highlighting the links between the processes and the "outside world" (see "Users & External Systems," Component 2.2 of the SCT), between processes and data stores, and among the processes themselves. These links are called data flows. Logically, they indicate the transfer of data, while practically, they involve the reading and writing of information to and from the database, input, output (queries and reports) and the transfer of files between databases. The DFD technique involves extensive use of a special type of flow diagram, and it is described in greater detail in the general technical literature.