Data Flow Diagrams Ramzy Kaoukdji

What is a Data Flow Diagram? - A graphical Representation of the flow of data through an information system, modeling its process aspects

What does it Represent Data Flow Diagram Represents the Following: 1)External devices sending and receiving data 2)Processes that change the data 3)Data flow themselves 4)Data storage locations

Components of a DFD A DFD usually consist of four main symbols to write a DFD

The Second Symbol:

The Third Symbol:

The Fourth Symbol:

This is what it would look like

What’s the difference Between Flow and DFD’s A DFD provides no information about the timing or ordering of processes, or about whether processes will operate in sequence or in parallel. A Flow Chart shows the flow of control through an algorithm, allowing a reader to determine what operations will be performed, in what order, and under what circumstances, but not what kinds of data will be input to and output from the system, nor where the data will come from and go to, nor where the data will be stored.

What are the Advantages of a DFD? Advantages: -A simple graphical technique which is simple to understand -Helps defining boundaries of the system -Useful for communicating current system knowledge -It helps explain the logic behind the flow of data and why information is transferred that way

Disadvantages -It can make the process slower because of the amount of times it undergoes alteration -Physical considerations are left out -Different DFD models can have the same symbols with different meanings

Example: Basic DFD

Example: Ordering a Book

Example of a DFD

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