DFD Slides
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The document discusses Data Flow Diagrams (DFDs) which are used to visualize the flow of data in information systems. It describes the key components of DFDs including processes, data flows, data stores, and external entities. Processes represent activities performed on data, data flows show the movement of data between processes and other components, data stores hold information used by the system, and external entities interact with the system from outside. The document provides rules for connecting these components and strategies for developing DFDs at different levels of abstraction.
DFD Slides
- 1. Data Flow Diagrams (DFDs)Data Flow Diagrams (DFDs) Creating data flow diagrams to understand business processes.
- 2. Data Flow Diagrams (DFDs)Data Flow Diagrams (DFDs) Data flow diagram (DFD) is a picture of the movement of data between external entities and the processes and data stores within a system
- 3. DFD Symbols (Gane & Sarson)DFD Symbols (Gane & Sarson) Process Data Flow Data Store Source/Sink (External Entity)
- 4. ProcessProcess Work or actions performed on data (inside the system) Labels should be verb phrases Receives input data and produces output
- 5. Rule 1: ProcessRule 1: Process Can have more than one outgoing data flow or more than one incoming data flow
- 6. Rule 2: ProcessRule 2: Process Can connect to any other symbol (including another process symbol)
- 8. Data StoreData Store Is used in a DFD to represent data that the system stores Labels should be noun phrases
- 9. Rule: Data StoreRule: Data Store Must have at least one incoming and one outgoing data flow
- 10. Source/Sink (External Entity)Source/Sink (External Entity) External entity that is origin or destination of data (outside the system) Is the singular form of a department, outside organisation, other IS, or person Labels should be noun phrases Source – Entity that supplies data to the system Sink – Entity that receives data from the system
- 11. Rule: Source/SinkRule: Source/Sink Must be connected to a process by a data flow
- 12. Rules for Using DFD SymbolsRules for Using DFD Symbols Data Flow That Connects YES NO 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
- 13. Context DiagramContext Diagram Top-level view of IS Shows the system boundaries, external entities that interact with the system, and major information flows between entities and the system. Example: Order system that a company uses to enter orders and apply payments against a customer’s balance
- 14. Level-0 DFDLevel-0 DFD Shows the system’s major processes, data flows, and data stores at a high level of abstraction When the Context Diagram is expanded into DFD level-0, all the connections that flow into and out of process 0 needs to be retained.
- 15. Lower-Level DiagramsLower-Level Diagrams Functional Decomposition ◦ An iterative process of breaking a system description down into finer and finer detail ◦ Uses a series of increasingly detailed DFDs to describe an IS Balancing ◦ The conservation of inputs and outputs to a data flow process when that process is decomposed to a lower level ◦ Ensures that the input and output data flows of the parent DFD are maintained on the child DFD
- 16. Strategies for Developing DFDsStrategies for Developing DFDs Top-down strategy ◦ Create the high-level diagrams (Context Diagram), then low-level diagrams (Level-0 diagram), and so on Bottom-up strategy ◦ Create the low-level diagrams, then higher- level diagrams
- 17. Exercise: Precision Tools sells a line of high-quality woodworking tools. When customers place orders on the company’s Web site, the system checks to see if the items are in stock, issues a status message to the customer, and generates a shipping order to the warehouse, which fills the order. When the order is shipped, the customer is billed. The system also produces various reports. Draw a context diagram for the order system Draw DFD diagram 0 for the order system
- 18. Identify Entities,Process,Data Stores & Data FlowIdentify Entities,Process,Data Stores & Data Flow Entities ◦ Customer ◦ Warehouse ◦ Accounting Processes ◦ 1.0 Check Status ◦ 2.0 Issue Status Messages ◦ 3.0 Generate Shipping Order ◦ 4.0 Manage Accounts Receivable ◦ 5.0 Produce Reports Data Stores ◦ D1 Pending Orders ◦ D2 Accounts Receivable Data Flows Order In-Stock Request Order Data Status Data Status Message Shipping Order Order Data Invoice Shipping Confirmation Payment Accounting Data Accounts Receivable Data Order Data Inventory Reports 1.0 2.0 3.0 4.0 5.0