dataflowdiagram-090322155640-phpapp01.ppt

How to: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,DFD Symbols(Gane&Sarson),Process,Data Flow,Data Store,Source/Sink(External Entity),Process,Work or actions performed on data(inside the system)Labels should be verb phrasesReceives input data and produces output,Rule 1:Process,Can have more than one outgoing data flow or more than one incoming data flow,Rule 2:Process,Can connect to any other symbol(including another process symbol),Process:Correct/Incorrect?,Data Flow,Is a path for data to move from one part of the IS to anotherArrows depicting movement of dataCan represent flow between process and data store by two separate arrows,Data Flow:Correct/Incorrect?,Data Store,Is used in a DFD to represent data that the system storesLabels should be noun phrases,Rule:Data Store,Must have at least one incoming and one outgoing data flow,Data Store:Correct/Incorrect?,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 personLabels should be noun phrases,Source Entity that supplies data to the systemSink Entity that receives data from the system,Rule:Source/Sink,Must be connected to a process by a data flow,Source/Sink:Correct/Incorrect?,Rules for Using DFD Symbols,Data Flow That Connects,YES,NO,List the errors of this DFD,Context Diagram,Top-level view of ISShows 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 customers balance,Context Diagram of Order System,Level-0 DFD,Shows the systems major processes,data flows,and data stores at a high level of abstractionWhen the Context Diagram is expanded into DFD level-0,all the connections that flow into and out of process 0 needs to be retained.,Context Diagram of Order System,Level-0 DFD of Order System,Lower-Level Diagrams,Functional DecompositionAn iterative process of breaking a system description down into finer and finer detailUses a series of increasingly detailed DFDs to describe an ISBalancingThe conservation of inputs and outputs to a data flow process when that process is decomposed to a lower levelEnsures that the input and output data flows of the parent DFD are maintained on the child DFD,Strategies for Developing DFDs,Top-down strategyCreate the high-level diagrams(Context Diagram),then low-level diagrams(Level-0 diagram),and so onBottom-up strategyCreate the low-level diagrams,then higher-level diagrams,Exercise:Precision Tools sells a line of high-quality woodworking tools.When customers place orders on the companys 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,Identify Entities,Process,Data Stores&Data Flow,EntitiesCustomerWarehouseAccountingProcesses1.0 Check Status 2.0 Issue Status Messages3.0 Generate Shipping Order4.0 Manage Accounts Receivable5.0 Produce ReportsData StoresD1 Pending OrdersD2 Accounts Receivable,Data FlowsOrderIn-Stock RequestOrder DataStatus DataStatus MessageShipping OrderOrder DataInvoice Shipping ConfirmationPaymentAccounting DataAccounts Receivable DataOrder DataInventory Reports,1.0,2.0,3.0,4.0,5.0,Context Diagram of Order System,Level-0 of Order System,