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Data Flow Diagrams
Techniques
10.13 Data Flow Diagrams
10.13.1 Purpose
10.13.2 Description
Data flow diagrams show where data comes from, which activities process the
data, and if the output results are stored or utilized by another activity or external
entity.
Data flow diagrams portray the transformation of data. They are useful for
depicting a transaction-based system and illustrating the boundaries of a physical,
logical, or manual system.
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A data flow diagram illustrates the movement and transformation of data
between externals (entities) and processes. The output from one external or
process is the input to another. The data flow diagram also illustrates the
temporary or permanent repositories (referred to as data stores or terminators)
where data is stored within a system or an organization. The data defined should
be described in a data dictionary (see Data Dictionary (p. 247)).
Data flow diagrams can consist of multiple layers of abstraction. The highest level
diagram is a context diagram which represents the entire system. Context
diagrams show the system in its entirety, as a transformation engine with
externals as the source or consumer of data.
Figure 10.13.1: Context Diagram Gane-Sarson Notation
External
Agent
Noun
Input Data
Input Data
Output Data
Output Data
Data Process
Verb/Noun
Phrase Naming
External
Agent
Noun
Input Data
Input Data
External
Agent
Noun
Output Data
Output Data
External
Agent
Noun
The next level of data flow diagrams is the level 1 diagram. Level 1 diagrams
illustrate the processes related to the system with the respective input data,
output transformed data, and data stores.
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