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Basic of DFD

Basic of DFD. Developing a DFD. There are no FIXED rules about how a DFD should be developed… There is no such a DFD call “CORRECT DFD”… Expert SAs may not need much…..but definitely need for YOU!!. Where to Begin Creating DFDs.

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Basic of DFD

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  1. Basic of DFD

  2. Developing a DFD • There are no FIXED rules about how a DFD should be developed… • There is no such a DFD call “CORRECT DFD”… • Expert SAs may not need much…..but definitely need for YOU!!

  3. Where to Begin Creating DFDs • Start with the data flow from an external entity and work forwards • Start with the data flow to an external entity and work backwards • Examine the data flows into or out of a data store • Examine data flows, entity connections and data stores associated with a particular process • Note fuzzy, ill-defined areas of the system for further clarification

  4. Description of Each Level • Context Diagram: This is the highest level and represents the overall system and its interaction with its environment • Level 0 Diagram: This shows the major subsystems and their interactions • Level x Diagram: Shows the processes that make up each of the major subsystems

  5. Level 0 Tips • Generally move from top to bottom, left to right • Minimize crossed lines • Iterate as needed • The DFD is often drawn many times before it is finished,even with very experienced systems analysts

  6. Level 0 DFD Building Procedure • Level-0 DFD • Identify what is being done between each input and its corresponding output • Identify the processes • Identify external data flows between external entities and processes • Identify internal data flows between processes and data stores

  7. When to Stop • Each process is a single decision or calculation or a single database operation, such as retrieve, update, create, delete or read. • Each data store represents data about a single entity such as a customer, employee, product or order. • The system user does not care to see any more detail or when you and other analysts have dcoumented sufficient detail to do subsequesnt systems development tasks. • Every data flow does not need to be split further to show that different data are handled in different ways. • You believe that you have shown each business form or transaction, computer screen and report as a single data flow. • You believe there is a separate process for each choice on all lowest-level menu options for the system.

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