Data flow diagram

Data flow diagram is used in software development. It shows the flow of data through the system. It has many levels but beyond level 2 complexity increases. It is used in software engineering, Business analysis, agile development & system structures etc. It can provide a detailed representation of a system. Used as a part of system documentation file. It is very easy to understand. It has many advantages but can make the programmers little confuse concerning the system & take long time 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 Yourdon & Coad Yourdon & DeMarco

6. Difference in Methods:

7. Components of DFDs External Entity Process Data Store Data Flow

8. Example Of a Banking Process Customer Enquires deposits & Withdrawals Account Details Counter 2 Account Information Account Information

9. Rules of Data Flow Data Can F low From External entity to process Process to external entity Process to data store Data store to process Process to process Data C annot F low 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 Logical Data Flow Diagram 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: Level 0 – Context Diagram Level 1 – Overview Diagram 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. 

19. Applications DFDs in Software Engineering DFDs in Business Analysis DFDs in Business Process Re-Engineering DFDs in Agile Development DFDs in System Structure

20. Advantages Aids in describing the boundaries of the system. B eneficial for communicating existing system knowledge to the users . C an provide a detailed representation of system components. U sed as the part of system documentation file. E asier to understand by technical and nontechnical audiences S upports the logic behind the data flow within the system.

21. 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 .