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data flow diagram DFD 0 AND dfd 1 FOR mis
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- 12. Data Flow Diagrams Presentedby Sarah Saad El deen 12
- 13. DFD LEVEL 0. Contextdiagram A context diagram is a data flow diagram that only shows the top level, otherwise known as Level 0. At this level, there is only one visible process node that represents the functions of a com plete system in regards to how it interacts with external entities. Som e of the benefits of a Context Diagram are: 1. Shows the overview of the boundaries of a system 2. No technical knowledge is required to understand with the sim ple notation 3. Sim ple to draw, am end and elaborate as its lim ited notation 13
- 14. 14 • The figureshows a context Data Flow Diagram that contains a process (shape) that represents the system to m odel, in this case, the "Food Ordering System". It also shows the participants interact with the system , called the external entities. • The Supplier, Kitchen, Manager, and Customer are the entities who will interact with the system . In between the process and the external entities, there is data flow (connectors) that indicate the existence of inform ation exchange between the entities and the system . • Context DFD is the entrance of a data flow m odel. It contains one and only one process and does not show any data store.
- 15. What is aData Flow Diagram? A data flow diagram (DFD) is a graphical representation of the movement of data between external entities, processes and data stores within a system. Simply put, DFD’s show how data moves through an information system. 15
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- 17. Process The work oractions performed on data so that they are transformed, stored, or distributed. Process labels should be verb phrases! 17 1.0 Produce Grade Report Grade Detail Grade Report
- 18. Data Flow A pathfor data to move from one part of the system to another. Data in motion! Arrows depict the movement of data. NO VERBS 18 2.1 Post Payment Accounts Receivable D1 Payment Detail Invoice Detail
- 19. Data Store Used ina DFD to represent data that the system stores Labels should be noun phrases (NO VERBS) 19 Students D1
- 20. External Entity akaSource/Sink The origin or destination of data! This represents things outside of the system. Source – Entity that supplies data to the system. Sink – Entity that receives data from the system. The labels should be noun phrases! 20 CUSTOMER 1.0 Verify Order Order Invoice
- 21. General DFD Rules 21 YESNO A process to another process A process to an external entity A process to a data store An external entity to another external entity An external entity to a data store A data store to another data store
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- 23. Example Customer canplace an Order. The Order Food process receives the Order, forwards it to the Kitchen, store it in the Order data store, and store the updated Inventory details in the Inventory data store. The process also delivers a Bill to the Customer. The Manager can receive Reports through the Generate Reports process, which takes Inventory details and Orders as input from the Inventory and Order data store respectively. The Manager can also initiate the Order Inventory process by providing Inventory order. The process forwards the Inventory order to the Supplier and stores the updated Inventory details in the Inventory data store. 23
- 24. Example Level 1DFD level 1 DFD, which is the decom position (i.e. break down) of the Food Ordering System process shown in the context DFD. 24
- 25. Data Flow DiagramTips and Cautions 1. Process labels should be verb phrases; data stores are represented by nouns 2. A data store m ust be associated with at least a process 3. An external entity m ust be associated with at least a process 4. Don't let it get too com plex; norm ally 5 - 7 average people can m anage processes 5. DFD is non-determ inistic - The num bering does not necessarily indicate sequence, it's useful in identifying the processes when discussing with users 6. Datastores should not be connected to an external entity, otherwise, it would m ean that you're giving an external entity direct access to your data files 7. Data flows should not exist between 2 external entities without going through a process 8. A process that has inputs but without outputs is considered to be a black-hole process 25
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- 29. Advantages of DFDs Simple graphical techniques which are easy to understand Helps define the boundaries of the system Useful for communicating current system knowledge to users Explains the logic behind the data flow within the system Used as the part of system documentation file 29
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