A data flow diagram (DFD) is a documentation tool which is used by systems
professionals to present the logical design of a system. The data flow emerged from the
management information system field and is used to depict a system process and data flows
among the process, and source, destinations and storage of data (Bradford, Richtermeyer,
Roberts, 2007). The advantage of DFDs is that they use only four symbols and are simple to
read and understand (Turner, Weickgenannt, 2009, p.60). There are two different types of
symbols, as shown below (Dunn, Cherrington, Hollander, 2005, p.107):
Gane and Sarson symbols
Yourdon and Coad symbols
Sources and destination of data.
Process
Storage of data
Data flow lines
Both logical and physical diagrams use the same set of symbols. The logical diagrams show
the conceptual flow of data without including any references to the physical characteristics
of the system. The physical diagrams include labels that describe physical attributes of the
system (Dunn, Cherrington, Hollander, 2005, p.106).
There are different levels of data flow diagrams. The highest level is the context diagram, also called
level-zero. A single system is represented on a context diagram and it provides the scope of the
system being represented. More levels can be created under level-zero if more details are need to
show about the process represented. Figure 1 and 2 shows the corresponding DFD of DVD rental
process:
Figure 1: Context DFD Level 0
Figure 2: Level 1 DFD
There are a few general rules that applied when creating DFD (Dunn, Cherrington, Hollander, 2005,
p.107 - 109):
1. All process should have unique names,
2. All process must have at least one data flows in and out,
3. Date must be moved by a process ,
4. Each data stored must be involved with at least one data flow,
5. Data cannot move directly form a source to a sink,
6. A data flow cannot go directly back to the same process it leaves,
7. A data flow must be linked to at least one process.
Diagramming tools combine the efficiency of graphics and rigor of rules to communicate the nature
of the process being modeled. It is important for analysts to develop the skills to both read and
create documentation of information and business processes using data flow diagrams.
References
Cheryl L. Dunn, J. O. (2005). Enterprise Information Systems: A pattern based approach
(third ed.). New York: McGraw-Hill/Irwin.
Marianne Bradford, S. B. (2007). System Diagramming Techniques: An Analysis of Methods
Used in Accounting Education and Pratice. Journal of Information Systems , 173 - 212.
Turner, W. (2009). Accounting Information Systems. United States of America: John Wiley &
Sons, Inc.
Yalin Zhu (1340076)
Vaiarava Terai (1341321)