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Data Flow Diagrams


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Data Flow Diagrams

  1. 1. DATA ANALYSISIdentifying the data needed for the business to operate is the nextstep. You need to find where the data comes from, what information isprocessing that data, and who the output goes to.Data-flow diagrams are the best way of showing how data works in asystemThe notation used for this is shown over the next few slides.
  2. 2. DATA STOREAny place where data is held. In a manualsystem this may be in an address book, adirectory, or a set of invoices; in a computer itis generally a file of some sort. D1 Customer
  3. 3. PROCESSAny action that causes something to happen to some data, makinga change or converting it into information. In a manual system thiscould be looking up a phone number in a directory, writing a phonenumber down in an address book, or calculating a total and puttingit at the bottom of an invoice. In a computer it could be automaticcalculation of the total, or producing a list of patients andappointment times. All processes have input and output –something going in and something coming out. With data-flowdiagrams, it is processes involving data that are included.
  4. 4. DATA FLOWUsed to show how data moves into, between and out ofprocesses, and between sources and recipients (destination) oddata. These may be people, institutions or other systems. Dataflow is not the physical article but the data that accompanies it –not the stock item itself, but the order, the picking list, the deliverynote, the bill/ or the receipt.
  5. 5. SOURCES OF DATA AND RECIPIENTSSources of data: Those external entities that provide data for the system. Thesemay be customers, who provide order details, or suppliers, whoprovide delivery notes and invoices.Recipients (destinations) of data: Those external entities who receive output from the system, butdo not directly use it. For example, government departmentsreceive tax returns from payroll systems, and VAT returns fromaccounting systems; the board of governors at a school receivesperformance and financial reports.
  6. 6. CONTEXT DIAGRAM / LEVEL 0 DFDData-flow diagrams can be drawn at different levels, to show levels of process. Ifa process is not a single step, a further Diagram is required to show thebreakdown. Each Process is numbered, with the system being numbered 0. Anexample for a catalogue system is shown over the next few slides. The diagrambelow shows a basic data flow from customer to the system. Rejected order 0 Custome Order r Catalogue System Goods
  7. 7. LEVEL 1 DFDThe level 1 data-flow diagram (DFD) below breaks the system into three mainprocesses, the first to check whether the customer is credit-worthy, the second todeal with the order of goods, finding them, picking them and sending them to thecustomer, and the third to maintain the credit details held for existing customers.The arrow with the question mark indicates that there needs to be some input forthis process, but as yet, the analyst does not know who or where this will comefrom. 1 Check credit rating Credit Order details Validated Rejected Order Custome 2 Order D1 Credit Rating r Dispatch Goods Goods ? 3 Maintain Credit Amended credit Rating details
  8. 8. LEVEL 2 DFDThe level 2 DFD for process 1 is shown below. Process 2 is likely to break downto at least one more level as well, more likely two or three more levels. Noticehow the numbering system works. The lines surrounding this DFD show theboundaries of the process - the external entity ‘Customer’ and the data store‘Credit rating’ are held outside the process. 1 Check Credit Rating 1.1 Order Credit Receive Order Details D1 Credit Rating Custome Received r Order 1.2 Check Cred. Status Reject Okay Order Order Rejecte d Order 1.3 1.4 Validated Order Send Rejection Send Order to Dispatch ?
  9. 9. FINALLY Data-flow diagrams may be used for documenting the current system, but are more useful when designing the proposed system.