A Data Flow Diagram (DFD) is a graphical representation that illustrates the flow of data in an information system, distinct from flowcharts as it does not include control elements. It has historical significance from the 1970s and is utilized in various applications like software engineering and business analysis, with different types including logical and physical DFDs. DFDs comprise components such as external entities, processes, data stores, and data flows, and while they have advantages in system documentation and communication, they can also be time-consuming to create.

1. Data Flow Diagram (DFD)
By Fizza Khan
Student of BS(Bioinformatics)

2. Data Flow Diagram:
• A data flow diagram (DFD) is a
graphical representation of the "flow" of
data through an information system,
modelling its process aspects.

3. History:
• In the 1970s, Larry Constantine, the original
developer of structured design, proposed
data flow diagrams as a practical technique
based on Martin and Estrin's "Data Flow
Graph" model of computation.
• It became more popular in business circles, as
it was applied to business analysis, than in
academic circles.

4. DFD is not a “Flow Chart”
• Flow chart shows “Flow of Control”.
• Data flow diagram shows “Flow of Data”.
• The flow chart describes boxes that describe
“Computation, Decisions, Interactions, &
Loops.
• Data flow diagram should not include control
elements.

5. Methods of Symbols used in
DFDs
1. Yourdon & Coad
2. Yourdon & DeMarco

6. Difference in Methods:

7. Components of DFDs
1. External Entity
2. Process
3. Data Store
4. Data Flow

8. Example Of a Banking Process
Custo
mer
Enquires
deposits &
Withdrawals
Account Details
Counter2
Account
Information
Account
Information

9. Rules of Data Flow
Data Can Flow From
• External entity to process
• Process to external entity
• Process to data store
• Data store to process
• Process to process
Data Cannot Flow From
• External entity to external
entity
• External entity to data store
• Data store to External
entity
• Data store to data store

10. Types Of Data Flow
Diagrams
1. Logical Data Flow Diagram
2. Physical Data Flow Diagram

11. Logical Data Flow Diagram
• It focusses on the business & how the business
operates.
• It describe the business events that take place & the
data required & produced by each event.
• It does not delve into the technical aspects of a
process or a system.
• Non-technical employees can understand these
diagrams easily.

12. Physical Data Flow
Diagrams
• It shows that the how system will be implemented.
• These diagrams specify the software, hardware, files
& people involved in an information flow.
• A detailed physical data flow diagram can facilitate
the development of the code needed to implement a
data system.

13. DFDs Levels & Layers:
1. Level 0 – Context Diagram
2. Level 1 – Overview Diagram
3. Level 2 – Detailed Diagram

14. Level 0 – Context Diagram
• It is the most basic & simplest Data Flow Diagram.
• It show a single process node and its connections to
external entities.
• This level basically represents the input & output of
the entire system.

15. Example of a Hotel Reservation
System

16. Level 1 – Overview Diagram
• Presents more detailed view of the system
than Level 0.
• Highlight the main functions carried out by
the system.
• It is basically the breakdown of level 0 into
sub-processes.

17. Example

18. Level 2 – Detailed Diagram
• Simply break processes down into more
detailed sub-processes.
• DFDs could go beyond level 3, but they rarely
do.
• Level 3 data flow diagrams are detailed
enough that it doesn’t usually make sense to
break them down further.

20. Applications
1. DFDs in Software Engineering
2. DFDs in Business Analysis
3. DFDs in Business Process Re-
Engineering
4. DFDs in Agile Development
5. DFDs in System Structure

21. Advantages
• Aids in describing the boundaries of the system.
• Beneficial for communicating existing system
knowledge to the users.
• Can provide a detailed representation of system
components.
• Used as the part of system documentation file.
• Easier to understand by technical and nontechnical
audiences
• Supports the logic behind the data flow within the

22. Disadvantages
• Make the programmers little confusing
concerning the system.
• The biggest drawback of the DFD is that it
simply takes a long time to create, so long
that the analyst may not receive support from
management to complete it.