MSc-IT Study Material
January 2011 Edition

Computer Science Department, University of Cape Town
| MIT Notes Home | Edition Home |

Chapter 6. Data-Flow Diagrams

Table of Contents

Introduction to data-flow diagrams
What are data-flow diagrams?
An example data-flow diagram
The benefits of data-flow diagrams
Case study
The different kinds (and levels) of data-flow diagrams
Elements of data-flow diagrams
Data stores
External entities
Multiple copies of entities and data stores on the same diagram
Context diagrams
What is a context diagram?
Constructing a context diagram
Level 1 data-flow diagrams
What is a level 1 DFD?
Constructing level 1 DFDs
Decomposing diagrams into level 2 and lower hierarchical levels
What is a level 2 (or lower) DFD?
Constructing level 2 (and lower) DFDs — functional decomposition
Making levels
Process descriptions
An example in constructing a data-flow diagram
Identify the system boundaries
Follow inputs
Follow events
Fill in gaps


At the end of this chapter you should be able to:

  • Explain the purpose of data-flow diagrams.

  • Describe the meaning of the symbols used in data-flow diagrams.

  • Describe the generic framework activities at which data flow diagrams can be used and the corresponding roles of data-flow diagrams in these stages.

  • Construct simple data-flow diagrams from a textual description.

  • Construct a levelled set of data-flow diagrams.

  • Understand how to check the consistency of related data-flow diagrams.