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Data Flow Diagram

Data Flow Diagram. Purpose – visually depict how data moves and changes through a top-down, logical model Logical model – requirements and the relationship among the requirements DFD is not program logic or processing logic. Data Flow Diagram. Data Flow Diagram. Leveling Top-down approach

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Data Flow Diagram

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  1. Data Flow Diagram • Purpose – visually depict how data moves and changes through a top-down, logical model • Logical model – requirements and the relationship among the requirements • DFD is not program logic or processing logic

  2. Data Flow Diagram

  3. Data Flow Diagram • Leveling • Top-down approach • General to detailed

  4. DFD Process Symbol • Processes change the data from one form to another form • Data is input for a process • Processes transform data to produce output

  5. DFD Process Symbol Rules • Place the name of the process inside the circle in ALL CAPS • The name identifies its function • The name consists of an active verb followed by a descriptive, single noun • APPLY DISCOUNT VERIFY ORDER

  6. DFD Process Symbol Rules • Process details are not shown • A process is a black box, as for as details are concerned • Levels of DFD (context / diagram 0)

  7. DFD Data Flow Symbol • A line with an arrowhead showing the direction of the data flow. • Purpose is to depict the pathway that data moves from one part of an information system to another part • Data Flow name identifies the data it represents

  8. DFD Data Flow Symbol • The name consists of adjectives and a singular noun • The line can be straight or curved • Each data flow equals a specific piece of data or a set of data (student name or class roster) • BANK DEPOSIT STUDENT GRADE

  9. DFD Data Flow Symbol • At least one data flow must enter each process symbol • At least one data flow must leave each process symbol • Often more than one

  10. DFD Data Store Symbol • The purpose is to depict a data repository • The plural name consists of adjectives and a noun • Place the data store name between the lines • STUDENTS PURCHASE ORDERS

  11. DFD Data Store Symbol • Data store is connected to a data flow with a proceses at the other end of the data flow • Detailed contents not shown in the DFD (find this information in the data dictionary)

  12. DFD External Entity Symbol • The purpose is to depict the terminators or boundaries • A person, department, outside organization, or other information system that provides data (orgin) to the system or recieves data (sink) or information from the system • Entity is always connected by a data flow to a process

  13. DFD External Entity Symbol • The entity name is in the singular form of the name of the department, outside organization, other information system or person • CUSTOMER STUDENT • PAYROLL SYSTEM

  14. Context Diagrams

  15. Context Diagrams • Top-level view of information system (IS) • First DFD is general overview of the IS • Shows the boundaries of the IS • One process only (it represents the entire IS) • Add all external entities and connect to process ORDER PROCESSING (process) CUSTOMER (entity) WAREHOUSE (entity) Page 160

  16. Context Diagrams • The requirements gathering of the systems analysis phase will define all the external entities • No data stores at this level of the DFD • Context diagram must fit on one page • Process name of the context diagram is the name of the IS • Avoid crossing data flow symbols

  17. Diagram 0 Diagram 0 for the context diagram DFD for a grading system.

  18. Diagram 0 • First detailed DFD • The purpose is depict the major processes, data flows, and data stores for an IS • Repeat the external entities and data flows from the context diagram • Add major processes and data stores

  19. Lower Level Diagrams • Expand all processes into functional primitives • Functional primitives are processes that consists of a single function ( can not expand further)

  20. Data Dictionary • The purpose is a central storehouse of data about an IS’s data and the data’s transformations • Dictionary is used to document the detailed facts about an IS Contents of data flows Contents of data stores External entities details

  21. Data Dictionary • Also defines and describes all data elements and meaningful combinations of data elements • A data element is the smallest piece of data that has meaning within an IS Salary student name Social security number birth date

  22. Data Elements • DFD data flow • DFD data store (data elements logically combined) • DFD process (functional primitive) • External entities (recommended)

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