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Data Flow Diagrams

Data Flow Diagrams. OWDA SHAQALIH. Common Errors in DFDs. Forgetting to include a data flow or pointing an arrowhead in the wrong direction Connecting data stores and external entities directly to each other Incorrectly labeling processes and/or data flow. Common Errors in DFDs.

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Data Flow Diagrams

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  1. Data Flow Diagrams OWDA SHAQALIH

  2. Common Errors in DFDs • Forgetting to include a data flow or pointing an arrowhead in the wrong direction • Connecting data stores and external entities directly to each other • Incorrectly labeling processes and/or data flow

  3. Common Errors in DFDs • Including more than nine processes on a DFD (not recommended) • Omitting data flow • Creating unbalanced decomposition in child diagram • each child diagram should have the same input and output data flow as the parent process • exception: minor output such as error lines

  4. Logical vs. Physical DFDs • DFDs are categorized as either • logical • physical • Logical DFDs • not concerned about how the system is or will be constructed • Physical DFDs • show how the system is or will be constructed

  5. Progression of Models Current Logical DFD New Logical DFD New Physical DFD

  6. Advantages of Logical DFDs • Better communication with users • More stable systems • Better understanding of the business by analysts • Flexibility and maintenance • Elimination of redundancies and easier creation of the physical model

  7. Advantages of Physical DFDs • Clarifying which processes are manual and which are automated • Describing processes in more detail than logical DFDs • Sequencing processes that have to be done in a particular order • Identifying temporary data stores • Specifying actual names of files and printouts • Adding controls to ensure the processes are done properly

  8. Partitioning DFDs • The process of analyzing a DFD and deriving a series of manual procedures and computer programs • A dashed line is drawn around a group of processes that are included in each computer program or manual procedure

  9. Why Partition ? • Different user groups should have different programs • Processes that execute at different time must be in separate programs • Similar tasks may be included in the same program • Several batch processes may be included in the same program for efficiency

  10. Why Partition ? • Several processes may be included in the same program or job stream for consistency of data • Processes may be separated into different programs for security

  11. Purposes of DFDs • Unexploded DFDs are useful to identify information requirements • Exploded DFDs can be used for • presentation • education • gathering feedback information from users

  12. Uses of DFDs • Used to analyze the system to ensure that the design is complete • Used to partition the system into programs • Used for system documentation

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