Data flow diagram(19th march)
Download as PPT, PDF0 likes2,069 views
The document defines and explains data flow diagrams (DFDs). DFDs show the flow of data through a system using common symbols like processes, data stores, external entities, and data flows. Processes represent actions performed on the data, data stores hold the data, external entities interact with the system, and data flows show movement of data. The document provides examples of how to construct DFDs and properly use the symbols to model a system at different levels of abstraction from context to lower level diagrams.
Data flow diagram(19th march)
- 2. Definition • In the late 1970s data-flow diagrams (DFDs) were introduced and popularized for structured analysis and design (Gane and Sarson 1979). • DFDs show the flow of data from external entities into the system, showed how the data moved from one process to another, as well as its logical storage.
- 3. Data Flow Diagram • Data flow diagram (DFD) is a picture of the movement of data between external entities and the processes and data stores within a system
- 4. Symbols and meaning • Squares representing external entities, which are sources or destinations of data. • Rounded rectangles representing processes, which take data as input, do something to it, and output it. • Arrows representing the data flows, which can either be electronic data or physical items. • Open-ended rectangles representing data stores, including electronic stores such as databases or XML files and physical stores such as or filing cabinets or stacks of paper.
- 5. DFD Symbols (Gane & Sarson) Process DataFlow DataStore Source/Sink (External Entity)
- 6. Example of DFD 1.0 Check Status 2.0 Issue Status Messages 3.0 Generate Shipping Order ACCOUNTING CUSTOMER WAREHOUSE 4.0 Manage Accounts Receivable 5.0 Produce Reports Order In-Stock Request Status Data Status Message Pending Orders D1 Order Data Order Data Shipping Order Shipping Confirmation Invoice Payment Accounts Receivable D2 Accounting Data Accounts Receivable Data Order Data Inventory Reports
- 7. Process Grade Detail 1.0 Produce Grade Report Grade Report • Work or actions performed on data (inside the system) • Labels should be verb phrases • Receives input data and produces output
- 8. Rule 1: Process • Can have more than one outgoing data flow or more than one incoming data flow 1.0 Grade Student Work Submitted Work Student Grade Graded Work 3.0 Calculated Gross Pay Pay Rate Hours Worked Gross Pay
- 9. Rule 2: Process Order Accepted Order 2.0 Assemble Order Inventory Change 1.0 Verify Order
- 10. Process: Correct/Incorrect? Services Perfomed 5.0 Create Invoice Invoice Apply Insurance Premium Policy Number Payment Amount Hours Worked 2.1 Calculate Gross Pay Pay Rate
- 11. Data Flow • Is a path for data to move from one part of the IS to another • Arrows depicting movement of data • Can represent flow between process and data store by two separate arrows 2.1 Post Payment Payment Detail Invoice Detail Accounts Receivable D1
- 12. Data Flow: Correct/Incorrect? Courses Class List Students 5.0 Post Payment Customer Payment D2 Daily Payments Daily Payment 6.0 Prepare Deposit
- 13. Data Store Students D1 • Is used in a DFD to represent data that the system stores • Labels should be noun phrases
- 14. Rule: Data Store • Must have at least one incoming and one outgoing data flow Customer Payment Daily Payments D1 Daily Payment
- 15. Data Store: Correct/Incorrect? 2.0 Book Flight Fight Request Passengers D2 Accounts Receivable Invoice Detail Payment Detail 3.0 Post Payment
- 16. Source/Sink (External Entity) CUSTOMER Invoice Order 1.0 Verify Order • 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
- 17. Rule: Source/Sink • Must be connected to a process by a data flow BANK Bank Deposit 2.0 Prepare Deposit
- 19. Rules for Using DFD Symbols • Data Flow That Connects 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 Yes No
- 20. List the errors of this DFD E1 E1 P2 P1 1.0 2.0 DS1 DF2 DF2 DF6 DF4 DF3 DF1 DF5
- 21. Context 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
- 22. Context Diagram of Order System 0 Order System SALES REP CUSTOMER WAREHOUSE BANK ACCOUNTING Order Order Reject Notice Picking List Completed Order Payment Invoice Commission Bank Deposit Cash Receipts Entry
- 23. Level-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.
- 24. 1.0 Fill Order 2.0 Create Invoice 3.0 Apply Payment SALES REP BANK ACCOUNTING CUSTOMER WAREHOUSE Order Order Reject Notice Picking List Accounts Receivable D1 Invoice Invoice Invoice Detail Payment Detail Payment Commission Bank Deposit Cash Receipts Entry Completed Order
- 25. Lower-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
- 26. Strategies 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
- 27. Exercise: M/S 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
- 28. Identify 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
- 29. Context Diagram of Order System ACCOUNTING WAREHOUSE CUSTOMER 0 Order System Order Payment In-Stock Request Status Message Invoice Shipping Confirmation Shipping Order Inventory Reports
- 30. 1.0 Check Status 2.0 Issue Status Messages 3.0 Generate Shipping Order ACCOUNTING CUSTOMER WAREHOUSE 4.0 Manage Accounts Receivable 5.0 Produce Reports Order In-Stock Request Status Data Status Message Pending Orders D1 Order Data Order Data Shipping Order Shipping Confirmation Invoice Payment Accounts Receivable D2 Accounting Data Accounts Receivable Data Order Data Inventory Reports