98 
Figure 8: Context diagram for the “integrated navigation” system 
22 Data flow diagram (DFD) 
Data flow diagrams represent the functional dependences between processes 6 in the form of ex 
changed information (data flows). Figure 9 shows the graphic symbols which are used to describe the 
logical components of a system in data flow diagrams. 
Processes are represented by circles with a name and a number, from which the manner of classifica 
tion in the hierarchical structure of the system considered is apparent. The hierarchical structure of data 
flow diagrams is based on the concept of progressive refinement. If the content of a process is describ- 
able in simple terms 7 , the refinement is terminated. Otherwise, it is divided into several sub-processes 
in the next refinement level (“partitioned”). This partitioning is described in part A. 
8 Since data flow diagrams are developed both for the task level and also for ail functionality/function levels, the 
term “process” is used on a general basis in the descriptive text. 
7 This means that the process concerned involved an elementary individual function (see [1]).