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Data Flow Diagrams (Continued)

Data Flow Diagrams (Continued). 23 January 2011. Data Flow Diagramming. This is a technique for organising and documenting the structure and flow of data through a system’s processes, and the procedures to be implemented by a system’s processes

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Data Flow Diagrams (Continued)

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  1. Data Flow Diagrams (Continued) 23 January 2011

  2. Data Flow Diagramming • This is a technique for organising and documenting the structure and flow of data through a system’s processes, and the procedures to be implemented by a system’s processes • Data flow diagrams are hierarchical in nature and may be decomposed into smaller, simpler sub-units at a lower level.

  3. DFD’s • Process • Represents an activity that changes or transforms data. • Data-Flow • Represents data in movement • External Entity/Agent • Represents an entity that lies outside the boundary of the system, which provides the system with data, or is served by the system. • Data-Store • Represents data at rest within the system, a data repository.

  4. Data Flow Diagrams • A system is rarely simple enough to be shown a single Data Flow Diagram, so a hierarchical set of DFDs are produced. • This is known as top-down modelling • Within the model Processes and Data are decomposed; Processes may be expressed as sub-processes and Data Flows in terms of sub-flows

  5. Context Level DFD • DFD’s move from the general to the specific • The first diagram allows the analyst to grasp the basic data movement • The initial context level diagram should be an overview

  6. Example of a Context Level DFD Context Level Data Flow Diagram Process B Entity A Entity

  7. Context Level DFD’s • A Context-Level DFD may also be known as a Level 0 DFD or a System Level DFD. • A Context Level DFD usually consists of only one process. • This process outlines exactly what the system does. • Identifying the entire system as a single process • Example: • Order Processing System • Application Processing System

  8. Big Burger Case: Big Burger is a large fast-food restaurant. The company have plans to automate their food ordering system. The demand for their food is growing and they have identified the opportunity to serve more customers each day and make more profit. Big Burger requires a system that will take customer orders, issue customers with receipts, send the orders to the kitchen, monitor goods sold and inventory and generate management reports.

  9. Example:Big Burger’s Food Ordering System CUSTOMER KITCHEN Customer Order 0 FOOD ORDERING SYSTEM Food Order Receipt Management Reports RESTAURANT MANAGER

  10. Big Burger Food Ordering System • Context Level DFD for the Big Burger Company. • At a high level: • The system is represented by a single process labelled 0. • The entities represent the environmental boundaries for the system.

  11. Data Flow Diagrams • A system is rarely simple enough to be shown a single Data Flow Diagram, so a hierarchical set of DFDs are produced. • This is known as top-down modelling • Within the model Processes and Data are decomposed; Processes may be expressed as sub-processes and Data Flows in terms of sub-flows

  12. Process Decomposition • A process => “work performed on, or in response to incoming data flows or conditions” (Laudon & Laudon, 2007) • Focus is on what work or action rather than who or what is doing the work or activity • e.g. what happens to data input. Not who is inputting it!!

  13. Process Decomposition • Process decomposition involves breaking down the system into smaller subcomponents • Why do this • what does it allow…e.g. • what are the benefits….e.g. • what about bridging that gap….anything to do with this…e.g.

  14. Composite Data Flow • Consists of other data flows • Allows for the combination of similar types of data flows on higher level data flow diagrams such as a context level diagram

  15. Higher Level Data Flow Process Order Customer ORDER Lower Level Data Flow Process Fast Track Order Customer ORDER Process Standard Order

  16. Level 1 DFDs • A decomposed graphical representation of the system from more general and higher level representations. • More specific

  17. Steps in Constructing DFDs • Page 73 of Tutorial Manual • Context level = Read narrative; assumptions; identify entities; highlight process; data flows; create diagram • Level 1 = Context Level Steps + Break the Process into sub processes; identify data stores; and construct diagram

  18. Big Burger Case: Big Burger is a large fast-food restaurant. The company have plans to automate their food ordering system. The demand for their food is growing and they have identified the opportunity to serve more customers each day and make more profit. Big Burger requires a system that will take customer orders, issue customers with receipts, send the orders to the kitchen, monitor goods sold and inventory and generate management reports.

  19. Context Level DFDBig Burger’s Food Ordering System CUSTOMER KITCHEN Customer Order 0 FOOD ORDERING SYSTEM Food Order Receipt Management Reports RESTAURANT MANAGER

  20. Level 1 DFD Big Burger’s Food Ordering System CUSTOMER KITCHEN 1 ?? ?? ?? ?? ?? 3 4 4 Management

  21. Draw in class - Level 1 DFD

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