Data flow diagrams (DFDs) visually represent how data flows through a system, highlighting transformations from inputs to outputs without addressing control flow or procedural details. DFDs can be hierarchically organized into leveled sets, where each level provides increasing detail about data processing. A data dictionary accompanies DFDs, identifying data flows uniquely and defining their relationships.

1. DATA FLOW
DIAGRAMS

2. Ɣ Also called Data Flow Graphs.
Ɣ Commonly used during Problem Analysis.
Ɣ A DFD shows the flow of data through a system.
Ɣ It views a system as a function that transforms the inputs into desired
outputs.
Ɣ Any complex system will not perform this transformation in a "single
VWHSë
Ɣ Data will typically undergo a series of transformations before it becomes
the output.
Ɣ The DFD aims to capture the transformations that take place within a
system to the input data so that eventually the output data is produced.

4. Ɣ A DFD is not a flowchart.
Ɣ DFD represents flow of data and not flow of control.
Ɣ A DFD does not represent procedural information.
Ɣ While drawing a DFD, procedural thinking must be consciously avoided.
Ɣ Considerations of loops and decisions must be ignored.
Ɣ In drawing the DFD, the designer has to specify the major transforms in the
path of the data flowing from the input to output.
Ɣ How those transforms are performed is not an issue while drawing the data

5. Leveled DFD Set
Ɣ Many systems are too large for a single DFD to describe the data
processing clearly.
Ɣ It is necessary that some decomposition and abstraction
mechanism be used for such systems.
Ɣ DFDs can be hierarchically organized.
Ɣ This helps in progressively partitioning and analyzing large systems.
Ɣ Such DFDs together are called a leveled DFD set.
Ɣ Each level has more information flow and data functional details
than the previous level.

6. Level-0 DFD
Ɣ Also called as Context Diagram.
Ɣ 5HSUHVHQWVHQWLUHVRIWZDUHVVWHPDVDVLQJOHêEXEEOHëZLWKLQSXW
and output data indicated by incoming and outgoing arrows.
Ɣ Data stores are not shown since they are within the system.

7. Level-1 DFD
Ɣ Level-0 DFD is decomposed into
multiple bubbles/processes.
Ɣ Data stores are included.
Ɣ Net inputs and outputs for a
process are the same as I/Ps and
O/Ps of the process in the
previous-level DFD.
Ɣ Refinement stops when each
EXEEOHLVFRQVLGHUHGêDWRPLFë

8. Data Dictionary
Ɣ In a DFD, data flows are identified by unique names. (All
components should be named uniquely)
Ɣ The data dictionary is a repository of various data flows defined
in a DFD.
Ɣ X = A+B : X consists of data elements A and B.
Ɣ X = A|B : X consists of either A or B.
Ɣ X = [A] : X consists of optional data element A.
Ɣ X = A*: X consists of one or more occurrences of A.

9. Example of a DD

10. Some common errors
Ɣ Unlabeled data flows
Ɣ Missing data flows; information required by a process is not
available
Ɣ Extraneous data flows; some information is not being used in the
process
Ɣ Consistency not maintained during refinement
Ɣ Missing processes
Ɣ Contains some control information

11. Example: Tic-Tac-Toe Game
Level-0 DFD

12. Level-1 DFD

13. Data Dictionary

14. Example: Restaurant System
Level-0 DFD
purify
-

15. Level-1 DFD
sale
info
)→_

16. Level-2 DFD

17. Data Dictionary

18. Example: Hotel Reservation System
Level-0 DFD

19. Level-1 DFD

20. Level-2 DFD

21. Example: Online Shopping System
Level-0 DFD

22. Level-1 DFD