Department of Electrical and Computer Engineering
Dalhousie University

Dataflow Diagrams: Construction and Layering

Dr. Larry Hughes


In Introduction to Dataflow Diagrams, the basic features and functions of dataflow diagrams were introduced. In this document, some suggestions as to how dataflow diagrams can be constructed are discussed.

It is worth noting that there are no hard and fast rules associated with dataflow diagrams (as with most things dealing with computer software), just common sense. Furthermore, it is worth remembering that different companies may use variations on the dataflow diagrams shown here; if you find yourself in this situation, remember to be be flexible.


Most practitioners of dataflow diagrams suggest that the following five issues be considered when creating DFDs:

Layering Dataflow Diagrams

In addition to the issues that should be considered when creating a dataflow diagram, there are several other techniques that can be employed to simplify their interpretation. Common sense suggests (as does one of the issues listed above), that dataflow diagrams should not look like:

The approach used by designers using DFDs is to represent the system as a series of layers, the topmost being the context diagram of the system. The context diagram is essentially the environment/system view; however, in this case, the environment consists of the various terminators that interact with the system:

Layering allows the problem to be partitioned into its various components: processes, stores, and terminators. These components can be linked together by the flows.

Once the context diagram has been completed, the first layer that makes up the system can be represented. This consists of the principal processes, stores, terminators, and flows. This layer is referred to as Figure 0:

Each process in Figure 0 must be given a number and a name; each process is then expanded into its own figure, using its process number from Figure 0. For example, Figure 2 would be written as:

The following are some suggested guidelines for writing layered dataflow diagrams:

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