The Analysis Process

Entity

• The rectangle is used to depict an external entity (a business, person or machine) that can send or receive data from the system.

• The external entity is also called a source or destination of data, and is considered to be external to the study.

Data Flow Lines

• The arrow shows movement of data from one point to another, with the head of the arrow pointing toward the data’s destination.

• Data flows occurring simultaneously can be depicted doing just that through the use of parallel arrows.

Process

• The circle is used to show the occurrence of a transforming process.

• always denote a change in or transformation of data; hence, the data flow leaving a process is always labeled differently than the one entering it.

• should be labeled accordingly using action verbs (gerund verbs).

Data Store

• The open-ended rectangle with a vertical line on the left side is used in data flow diagrams, which represents a data store.

• These are drawn only wide enough to allow lettering between the parallel lines.

• the type of physical storage (i.e. tape, diskette, hard disk, etc.) is not specified.

• the data store symbol is simply showing a repository of data that allows updating and retrieval of data.

Levels of Data Flow Diagrams

1. Context Diagram

2. Top Level Diagram

3. Explosions

Context Diagram

• Shows the overview of the system

• Includes all external entities, inputs and outputs.

• A big process symbol is used to denote the name of the information system being studied.

Top Level Diagram

• Shows all the external entities, input and output data flow lines as well as the major processes involved.

• Data stores are also shown in this diagram.

• Processes shown are the major processes only, about 4 – 6 are ideal number of processes.

Explosions

• Break down a major process into its detailed sub-processes, including their input and output data flow lines.

• Data stores are also included if necessary.

• The entities are no longer shown in this diagram.