How to Draw Data Flow Diagram

Creating the Context Diagram :

• The highest level in a data flow diagram
• Contains only one process, representing the entire system
• The process is given the number 0
• All external entities, as well as Major data flows are shown

Drawing Diagram 0:

• The explosion of the context diagram
• May include up to nine processes
• Each process is numbered
• Major data stores and all external entities are included
• Start with the data flow from an entity on the input side
• Work backwards from an output data flow
• Examine the data flow to or from a data store
• Analyze a well-defined process
• Take note of any fuzzy areas

Data Flow Diagram Levels:

• Data flow diagrams are built in layers
• The top level is the Context level
• Each process may explode to a lower level
• The lower level diagram number is the same as the parent process number
• Processes that do not create a child diagram are called primitive

Creating Child Diagrams:

• Each process on diagram 0 may be exploded to create a child diagram
• A child diagram cannot produce output or receive input that the parent process does not also produce or receive
• The child process is given the same number as the parent process
• Process 3 would explode to Diagram 3
• Entities are usually not shown on the child diagrams below Diagram 0
• If the parent process has data flow connecting to a data store, the child diagram may include the data store as well
• When a process is not exploded, it is called a primitive process