DFD

Data Flow Diagrams
Flow based model
Determines the flow of the program and its processes
Level wise approach

Syntax

Shapes	Purpose
Rectangle	External Entity
Circle / Bubble	Processes
Parallel Lines	Data Store
Arrows	Data Items

Syntactical Rules

• The processes names should start with verb
• The variables can be provided with a single arrow as a list separated by commas

Levels

Levels can be dragged to any number starting from 0
There should be continuity between levels
Each level is an abstraction of the previous level. This means that it describes the processes involved in the previous level.

• The data items used in higher levels should include the items from the lower levels
  • The data items can be detailed but they should exist in an upper set context in the lower levels.
    • The Examples could be Login Info to username, password

DFD Level 0

• Is the system itself
  • So the the label of the bubble doesn’t have to start with a verb
• Consists of a single bubble
• No data stores

Further Levels

• Follows the same ruling conventions as described above.

Example