Following are the rules which are needed to keep in mind while drawing a DFD(Data Flow Diagram).
- Data can not flow between two entities. –
Data flow must be from entity to a process or a process to an entity. There can be multiple data flows between one entity and a process.
- Data can not flow between two data stores
Data flow must be from data store to a process or a process to an data store. Data flow can occur from one data store to many process.
- Data can not flow directly from an entity to data store –
Data Flow from entity must be processed by a process before going to data store and vice versa.
- A process must have atleast one input data flow and one output data flow –
Every process must have input data flow to process the data and an output data flow for the processed data.
- A data store must have atleast one input data flow and one output data flow –
Every data store must have input data flow to store the data and an output data flow for the retrieved data.
- Two data flows can not cross each other.
- All the process in the system must be linked to minimum one data store or any other process.
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