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Data Flow diagrams & systems flowcharts
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Once the systems analysts have completed their investigation they produce a detailed description of how the existing system works.

Methods used to help describe the system include data flow diagrams and systems flowcharts

Symbols used in DFDs

symbols in dataflow diagrams 

External entity (symbol1 - top)– data source or data destination, for example people who generate data such as a customer order, or receive information such as an invoice.

Process (symbol2) – an operation performed on the data. The two lines are optional; the top section of the box can be used to label the process, the middle to give a brief explanation, the bottom to say where the process takes place.

Data store (symbol3) – such as a file held on disk or a batch of documents

Data flow (symbol4 - bottom) – the arrow represents movement between entities, processes or data stores. The arrow should be labelled to describe what data is involved.

Data flow diagram for a theatre booking system.

data flow diagram 

The symbols used in flowcharts

flowchart symbols 

A systems flowchart

 systems flowchart

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