1. Data Flow Diagram
A method used to analyze a system in a structured way
Used during:
Analysis stage: to describe the current system
Design stage: to describe the proposed solution

2. Data Flow Diagrams (DFD)
A graphical representation of how the data is moving inside the system or organization
Advantages
Graphics is better in showing the relationship between subsystems
Easier for the user to validate
Easy to check if there is some information missing
Free from implementation details

3. DFD Symbols External Entity| Entity Process Data Flow Data Store
Anything in the system which receives or originates data
Process
Action done on data (data format changes)
Data Flow
Data is being moved from one point to another
Data Store
Manual or computerized
Name
Unique No.
Name
Label
Unique
No.
Name

4. Steps to Create DFD Make a list of business activities
Create a context diagram
Create diagram 0
Create child diagrams
Check for errors in diagrams
Go back to the user when you have unclear areas

5. Context Diagram A diagram which shows the system and its boundaries
Shows overview of the system
All external entities
One general process that represents the whole system

6. Diagram 0 Shows major processes in the system Shows external entities
Shows major data stores
All the input and output data in diagram 0 should be consistent with context diagram

7. Child Diagrams
Each complex process in diagram 0 will have a child diagram to show its details
Process that expands into child diagram is called “parent process”
Includes data stores and sub processes
Includes exception handling processes
No external entities are shown in child diagrams
Primitive process: a process that doesn’t have a child diagram

9. Rules for DFD A process should have at least one input and one output
Do not connect an entity to another or to a data store directly
Diagram 0 should not have more than 9 processes
Give unique numbers to processes and data stores
Give meaningful names to symbols

10. Rules for DFD
Check the consistency of data flow between context diagram and diagram 0
Child diagram should have the same input/output as the parent diagram
Process names should have an action (verb)
Data flow labels should be nouns and should not be too long

11. DFD Types Logical Physical Describes business operation
Used during analysis to better understand the analyzed system and to communicate with the users
Processes are business activities
Physical
Describes system implementation
Used during the design stage
Processes are program modules

13. Partitioning a DFD
After finishing the DFD, analyze it and partition processes according to their types
Draw dashed lines to partition
Partition process that are:
Done by different users
Done at different times
Needs different security operations
Working on same data

14. Partition a DFD Manual process Batch process
Processes that follow each other from a data store
Online or interactive process
Job streaming process
Programs running back-to-back
Look at the input output of the processes, if on line, get input from people or manual process. If batch input and output from data stores