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Logical Dataflow Diagrams (DFDs)

Logical Dataflow Diagrams (DFDs). Context DFD. Physical DFD. Logical DFD. A Reminder. Vocabulary of DFDs. Bubble. The System. Internal Entity. Process. External Entity. External Entity. External Entity. Square. N/A. File. File. Data Flow or “connector”. Data Flow.

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Logical Dataflow Diagrams (DFDs)

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  1. Logical Dataflow Diagrams(DFDs)

  2. Context DFD Physical DFD Logical DFD A Reminder... Vocabulary of DFDs Bubble The System Internal Entity Process External Entity External Entity External Entity Square N/A File File Data Flow or “connector” Data Flow Data Flow

  3. The Basic Idea Guidelines for DFDs • The idea is that we would like to group activities that “belong together” into processes. • Note that a process is a just set of related activities. • The SYSTEM itself is just a set of activities, too. • There are no ENTITIES now.

  4. How to Do It Guidelines for DFDs • The approach is easy - • Sort the list of activities chronologically - I usually just write down the numbers in chronological order (we actually already did this) • Break it into processes by deciding upon “division points” between processes. This is TOTALLY up to you. There is not necessarily a right answer. The only rule is that every process must have at least ONE activity. • Write F over each number that is a file activity and E over each number that is a data flow to or from an external entity. Do not worry about data flows between internal entities.

  5. How to Do It Guidelines for DFDs An Example - Causeway EF F FEFE 1, 2, 3, 4, 5, 6, 7, 8, 17, 13, 14, 15, 16, 11, 12, 18, 19, 9, 10

  6. How to Do It Guidelines for DFDs • You would decide how many processes there were by intuition (but you do not need to worry about that for this class). For real life situations, the general rule of thumb is 5 to 7 bubbles. You will typically have between 3 and 4 for this class. • There would be one bubble for each process and they would be numbered 1.0, 2.0, 3.0, etc. (again, these will be given for this class). • Draw arrows from bubble 1.0 to bubble 2.0 and from bubble 2.0 to 3.0, etc. THESE WILL NOT BE LABELED. • Draw necessary arrows to and from the “appropriate bubble” to and from (1) external entities and (3) files.

  7. 1 Checks & R/As Customers 14 17 13 Txn Data Acc Rec. G/L Office 18 Bank 10 Deposit Total of C/R 12 Causeway 1.0 Open Mail 2.0 Record A/R 4.0 Complete Cash Receipts 3.0 Prepare Deposit EF F FEFE 1, 2, 3, 4, 5, 6, 7, 8, 17, 13, 14, 15, 16, 11, 12, 18, 19, 9, 10

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