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


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