1. Data Flow Diagrams A data flow diagram is a tool that depicts the flow of data through a system and the work or processing performed by the system.

2. DFD Vs Flow Charting I) Processes on a data flow diagram can operate in parallel. Processes on a data flow diagram can operate in parallel. Processes on a flow chart can operate only one at a time Processes on a flow chart can operate only one at a timeII) Data flow diagrams shows the flow of data through the system Data flow diagrams shows the flow of data through the system Flow charts shows the sequence of processes or operations in an algorithm. Flow charts shows the sequence of processes or operations in an algorithm.

3. Illegal data flows B1 B2

4. B1

7. What is process? A process is work performed on, or in response to, in coming data flows or conditions A process is work performed on, or in response to, in coming data flows or conditions

8. Process symbols Gene & Sarson shape

9. SSADM / IDEF 0 SSADM / IDEF 0

10. Process Symbols Demarco / Yourdon shape Demarco / Yourdon shape

11. Legal Data Flows B1 A process is needed To exchange data flows between External agents B2

12. B1 A process is needed To update a data store

13. A Process is needed to present data from A data store B1

14. A process is needed To present data from a data store

15. Rules to follow to write DFD’s Establish the context of the data flow diagram by identifying all of the net input and output data flows Establish the context of the data flow diagram by identifying all of the net input and output data flows Select a starting point for drawing the data flow diagram from inputs to outputs Select a starting point for drawing the data flow diagram from inputs to outputs Backwards from output to input Backwards from output to input Give meaningful labels to all dataflow lines Give meaningful labels to all dataflow lines Label all process with action verbs that relate input and output data flows Label all process with action verbs that relate input and output data flows

16. Rules to follow to write DFD’s Omit insignificant functions routinely handled in the programming process Omit insignificant functions routinely handled in the programming process Do not include control or flow of control information Do not include control or flow of control information Do not try to put too much information in one data flow diagram Do not try to put too much information in one data flow diagram