3Systems ModelingEnterprise Model graphically represents organizational entities and the relationships between entitiesA process model represents a system’s functions (data flow diagrams)A data model represents a system’s data and the relationships between data elements (entity relationship diagram)An object model represents a system’s classes including attributes, methods and relationships
4Process ModelingGraphically represent the processes that capture, manipulate, store, and distribute data between a system and its environment and among system componentsUtilize information gathered during requirements determinationProcesses and data structures are modeled
5Pizza Delivery Example 4. confirmationCustomer1. Coupon, orderaddresspayment typeSales2. wait time3. order details10. PizzaDatabase5. order11. Payment7. addressChef9. Pizza collected6. order done12. Payment receivedDelivery8. Pizza
6Doors-R-Us Service Example Process:MaterialsManager8.WorkOrderDispatcherAccountsReceivableClerk9.Installer10.7.6.11.ReceptionistBill2.Customer5.1.3.Salespeople4.QuoteEstimator
7Doors-R-Us Process Explanation 1. Salespeople get potential customers familiar with company/services2. When potential customer needs a door service, they call HQ, get the receptionist3. Receptionist finds estimator (HQ /road) to visit customer and assess situation4. Estimator inspects site and submits quote to warehouse manager5. If customer decides to use Doors-R-Us, calls HQ (receptionist) to request service6. Receptionist finds dispatcher to schedule the work7. Dispatcher and customer agree on time for service
8Doors-R-Us Process Explanation 8. Dispatcher gets needed supplies from Materials Manager9. Dispatcher sends an installer to get the replacement door and install it10. Installer writes up a work order and submits to A/R Clerk11. A/R Clerk sends bill to Customer
9Process Modeling Deliverables and Outcomes Context data flow diagram (DFD)Scope of systemDFDs of current physical and logical systemEnables analysts to understand current systemDFDs of new logical systemTechnology independentShow data flows, structure, and functional requirements of new systemThorough description of each DFD component
10Data Flow Diagram (DFD) A picture of the movement of data between external entities and the processes and data stores within a systemDifference from system flowcharts:DFDs depict logical data flow independent of technologyFlowcharts depict details of physical systems
12Data Flow Symbols (cont.) Data StoreDepicts data at restMay represent data inFile folderComputer-based fileNotebookThe name of the store as well as the number are recorded in between lines8.12
13Data Flow Symbols (cont.) ProcessDepicts work or action performed on data so that they are transformed, stored or distributedNumber of process as well as name are recordedData flow: arrows depicting movement of data8.13
14Data Flow Symbols (cont.) Source/SinkDepicts the origin and/or destination of the dataSometimes referred to as an external entityDrawn as a square symbolName states what the external agent isBecause they are external, many characteristics are not of interest to us8.14
15DFD Diagramming Rules Process No process can have only outputs or only inputs…processes must have both outputs and inputs.Process labels should be verb phrases.
16DFD Diagramming Rules Data Store All flows to or from a data store must move through a process.Data store labels should be noun phrases.
17DFD Diagramming Rules Source/Sink No data moves directly between external entities without going through a process.Interactions between external entities without intervening processes are outside the system and therefore not represented in the DFD.Source and sink labels should be noun phrases.
18DFD Diagramming Rules Data Flow Bidirectional flow between process and data store is represented by two separate arrows.Forked data flow must refer to exact same data item (not different data items) from a common location to multiple destinations.
19DFD Diagramming Rules Data Flow (cont.) Joined data flow must refer to exact same data item (not different data items) from multiple sources to a common location.Data flow cannot go directly from a process to itself, must go through intervening processes.
20DFD Diagramming Rules Data Flow (cont.) Data flow from a process to a data store means update (insert, delete or change).Data flow from a data store to a process means retrieve or use.Data flow labels should be noun phrases.
21Functional Decomposition An iterative process of breaking a system description down into finer and finer detailHigh-level processes described in terms of lower-level sub-processesDFD charts created for each level of detail
22DFD Levels Context DFD Level-0 DFD Level-1 DFD Level-n DFD Overview of the organizational systemLevel-0 DFDRepresentation of system’s major processes at high level of abstractionLevel-1 DFDResults from decomposition of Level 0 diagramLevel-n DFDResults from decomposition of Level n-1 diagram
23Context DiagramContext diagram shows the system boundaries, external entities that interact with the system, and major information flows between entities and the system.NOTE: only one process symbol, and no data stores shown.
24Level-0 DFDLevel-0 DFD shows the system’s major processes, data flows, and data stores at a high level of abstraction.Processes are labeled 1.0, 2.0, etc. These will be decomposed into more primitive (lower-level) DFDs.
25Level-1 DFDLevel-1 DFD shows the sub-processes of one of the processes in the Level-0 DFD.This is a Level-1 DFD for Process 4.0.Processes are labeled 4.1, 4.2, etc. These can be further decomposed in more primitive (lower-level) DFDs if necessary.
26Level-n DFDLevel-n DFD shows the sub-processes of one of the processes in the Level n-1 DFD.This is a Level-2 DFD for Process 4.3.Processes are labeled 4.3.1, 4.3.2, etc. If this is the lowest level of the hierarchy, it is called a primitive DFD.
28A Simple DFD Example: Customer Order Process for CD On-Line Customers select the CDs they would like to order and communicate their selected CD item numbers and their customer account number to CD On-Line. Based on the customer’s selection, the order is processed by calculating the order total amount.The order total and customer account number as well as the customer’s old credit balance (from the customer credit database) are used to update the customer’s new credit balance. The new balance should be recorded on the customer credit database.
29A Simple DFD Example: Customer Order Process for CD On-Line (cont’d) The detailed order data from order processing and updated customer credit balance information are used to prepare a customer invoice and invoice information is updated. Detailed invoice data are used to prepare a shipping list and the invoice is sent to the customer on-line. The shipping list information is sent to UPS. (Based on a partnership relationship between CD On-Line and UPS, UPS warehouses the CDs and ships the CDs to the customers based on the shipping list).
30Translating into DFD Vocabulary External EntitiesCustomerUPSInternal Entity: CD On-LineData StoreCustomer credit
31Translating into DFD Vocabulary ProcessCompute order totalUpdate customer credit account balancePrepare invoicePrepare shipping listData FlowsCD item numbersCustomer account numberOld/New balanceOrder data
32DFD BalancingThe conservation of inputs and outputs to a data flow process when that process is decomposed to a lower levelBalanced means:Number of inputs to lower level DFD equals number of inputs to associated process of higher-level DFDNumber of outputs to lower level DFD equals number of outputs to associated process of higher-level DFD
33Unbalanced DFD1 input1 outputThis is unbalanced because the process of the context diagram has only one input but the Level-0 diagram has two inputs.2 inputs1 output
34Balanced DFD 1 input 2 outputs These are balanced because the numbers of inputs and outputs of context diagram process equal the number of inputs and outputs of Level-0 diagram.
35Balanced DFD (cont.)These are balanced because the numbers of inputs and outputs to Process 1.0 of the Level-0 diagram equals the number of inputs and outputs to the Level-1 diagram.1 input4 outputs
36Data Flow SplittingA composite data flow at a higher level may be split if different parts go to different processes in the lower level DFD.This remains balanced because the same data is involved, but split into two parts.
38Four Different Types of DFD Current PhysicalProcess labels identify technology (people or systems) used to process the data.Data flows and data stores identify actual name of the physical media.Current LogicalPhysical aspects of system are removed as much as possible.Current system is reduced to data and processes that transform them.
39Four Different Types of DFD (cont.) New LogicalIncludes additional functionsObsolete functions are removedInefficient data flows are reorganizedNew PhysicalRepresents the physical implementation of the new system
44Do we need all four DFDs? Focus on new logical (then start)! Make all only whenAnalysts know little about the user’s businessUsers cannot start with new logical DFDLittle works for conversion from old logical DFD to New DFDDon’t waste too much time on details of current DFDs.
45Guidelines for Drawing DFDs CompletenessDFD must include all components necessary for system.Each component must be fully described in the project dictionary or CASE repository.ConsistencyThe extent to which information contained on one level of a set of nested DFDs is also included on other levels.
46Guidelines for Drawing DFDs (cont.) TimingTime is not represented well on DFDs.Best to draw DFDs as if the system has never started and will never stop.Iterative DevelopmentAnalyst should expect to redraw diagram several times before reaching the closest approximation to the system being modeled.
47Guidelines for Drawing DFDs (cont.) Primitive DFDsLowest logical level of decompositionDecision has to be made when to stop decomposition
48Guidelines for Drawing DFDs (cont.) Rules for stopping decompositionWhen each process has been reduced to a single decision, calculation or database operationWhen each data store represents data about a single entityWhen the system user does not care to see any more detail
49Guidelines for Drawing DFDs (cont.) Rules for stopping decomposition (continued)When every data flow does not need to be split further to show that data are handled in various waysWhen you believe that you have shown each business form or transaction, online display and report as a single data flowWhen you believe that there is a separate process for each choice on all lowest-level menu options
50Using DFDs as Analysis Tools Gap AnalysisThe process of discovering discrepancies between two or more sets of data flow diagrams or discrepancies within a single DFDInefficiencies in a system can often be identified through DFDs.
51Using DFDs in Business Process Reengineering Example: IBM CreditSee Figure 7-20 – before reengineeringCredit approval process required six days before BPRFigure 7-21 depicts DFD after reengineeringIBM was able to process 100 times the number of transactions in the same amount of time
52Using DFDs in BPRAfter: process 100 times as many transactions in the same timeBefore: Credit approval process required six days
53Oracle’s Process Modeler and Functional Hierarchy Diagrams Unique to OracleSimilar to DFDS but outputs and methods differ in several ways.Table 8-4 illustrates differencesFunctional Hierarchy DiagramsPicture of various tasks performed in a business and how they are relatedTasks are broken down into their various partsDoes not include data flows
55An Exercise on Your Own 1 Customer Payment Process for CD On-Line Customers make payments for their purchases by sending checks along with their customer account numbers. The payments are processed by recording the payment.The payment data as well as the customer’s old credit balance (from the customer credit database) are used to update the customer’s new credit balance. The new balance should be recorded on the customer credit database. Also, a receipt is sent to the customer.The payment data from payment recording processing are used to make bank deposit. The deposit data are sent to banks.