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System Analysis and Design System Analysis - Mr. Ahmad Al-Ghoul Learning Objectives Discuss and draw the Lower-Level Diagrams Explain how to level and balance a set of data flow diagrams Explain when to stop leveling Explain how to validate the DFDs Distinguish between logical and physical DFDs Avicenna System Analysis and Design System Analysis 2 Creating a Set of DFDs Draw the Lower-Level Diagrams Business processes are too complex to be shown on a single DFD Must use leveling and balancing techniques leveling is the process of representing the system in a hierarchy of DFD diagrams Uses a series of increasingly detailed DFDs to describe an information system Avicenna leveling also is called Exploding, partitioning, or decomposing Child diagrams show a portion of the parent diagram in greater detail System Analysis and Design System Analysis 3 Creating a Set of DFDs Draw the Lower-Level Diagrams Avicenna Data flow diagrams are built in layers The top level is the Context level Each process may explode to a lower level The lower level diagram number is the same as the parent process number Each process on diagram zero may be exploded to create a child diagram Each process on a lower-level diagram may be exploded to create another child diagram These diagrams found below Diagram 0 are given the same number as the parent process System Analysis and Design System Analysis 4 Creating a Set of DFDs Draw the Lower-Level Diagrams Avicenna Each process is numbered with the parent diagram number, a period, and a unique child diagram number If the parent process has data flow connecting to a data store, the child diagram may include the data store as well A lower-level diagram may contain data stores not shown on the parent process System Analysis and Design System Analysis 5 Creating a Set of DFDs Level 1 DFD for process1, shows details of the FILL ORDER process in the order system. The FILL ORDER consists of three processes, VERIFY ORDER, PREPARE REJECT NOTICE, and ASSEMBLE ORDER Two data stores CUSTOMERS and PRODUCTS Depending on the processing logic A CUSTOMER submit an ORDER, the VERIFY ORDER requires PRODUCT DETAIL from PRODUCTS data store and CREDIT STTUS from CUSTOMERS data store, apply either REJECTED NOTICE to PREPARE REJECT NOTICE process or ACCEPTED ORDER to ASSEMBLE ORDER process as output If the order rejected, PREPARE REJECT NOTICE sends ORDER REJECTED NOTICE to the CUSTOMER entity and CREDIT HISTORY to the CUSTOMERS data store If the order accepted, ASSEMPLE ORDER process requires PICKING DETAIL from PRODUCTS data store, apply both PICKING LIST to WAREHOUSE entity and INVENTORY CHANGE to PRODUCTS data store, as outputs Avicenna System Analysis and Design System Analysis [1] 6 Creating a Set of DFDs Level 1 DFD for process 3, shows details of the APPLY PAYMENT process in the order system. The APPLY PAYMENT consists of four processes, POST PAYMENT, DEPOSIT PAYMENT, PREPARE ACCOUNTING ENTERY, and PAY COMMISSION Two data stores ACCOUNTS RECEIVABLE and DAILY PAYMENTS Depending on the processing logic A CUSTOMER submit a PAYMENT, the POST PAYMENT process requires INVOICE DETAIL from ACCOUNTS RECEIVABLE data store, apply both CUSTMER PAYMENT to the DAILY PAYMENT data store and PAYMENT DETAIL to the ACCOUNTS RECEIVABLE data store as outputs DEPOSIT PAYMENT requires DAILY PAYMENT from DAILY PAYMENTS data store, apply BANK DEPOSIT to the BANK entity as output PREPARE ACCOUNTING ENTERY requires ACCOUNTING PAYMENT from DAILY PAYMENTS data store, apply CASH RECEIPT ENTERY as output to the ACCOUNTING entity PAY COMMISSION requires COMMISSION EARNED from POST PAYMENT process, apply COMMISSION as output to the SALES REP entity Avicenna System Analysis and Design System Analysis [1] 7 Creating a Set of DFDs when to stop leveling : if a process has a single input data flow or a single output data flow then it should be apparent that there is little point in leveling it any further. when a process can be accurately described by a single active Avicenna verb with a singular object, this also indicates that the level has been carried out to a sufficiently low level. When you believe that there is a separate process for each choice on all lowest-level menu options, ask yourself if anything useful will be gained by further leveling of a process. Would any more detail influence your decisions? If the answer is no, then there is little point in taking the leveling further. System Analysis and Design System Analysis 8 Data Flow Diagrams Balancing Avicenna involves insuring that information presented at one level of a DFD is accurately represented in the next level of a DFD. DFD level 0 must have the same inputs and outputs as context diagram Process 1.0, which appears in a level 0 diagram, must have the same inputs and outputs when decomposed into a level 1 diagram, the same thing for the other processes in level o System Analysis and Design System Analysis 9 Data Flow Diagrams Validating the DFD Syntax errors Assure correct DFD structure Semantics errors Assure accuracy of DFD relative to actual and desired business processes Avicenna User walkthroughs Examine lowest level DFDs to ensure consistent decomposition Examine names carefully to ensure consistent use of terms System Analysis and Design System Analysis 10 Logical Versus Physical DFDs While structured analysis tools are used to develop a logical model for a new information system, such tools also can be used to develop physical models of an information system Logical data flow diagrams show how the business operates They have processes that would exist regardless of the type of system implemented Physical data flow diagrams show how the system operates or how the new system will be implemented Physical data flow diagrams include Avicenna Clarifying which processes are manual and which are automated Describing processes in greater detail Sequencing processes in the order they must be executed System Analysis and Design System Analysis 11 Sequence Summary Lower level DFDs show additional detail of the information system through the leveling technique of numbering and partitioning Leveling continues until you reach the the functional primitive processes, which are not decomposed further All diagrams must be balanced to ensure their consistency and accuracy Avicenna System Analysis and Design System Analysis 12 Sequence Summary In this Sequence we have Avicenna Explained how to draw level 1 and the Lower-Level Diagrams Defined the terms leveling and balancing Explained how to level and balance a set of data flow diagrams Explained when to stop leveling Explained how to validate the DFDs Distinguish between logical and physical DFDs System Analysis and Design System Analysis 13 Reference [1] System Analysis and Design, Sixth Edition Authors: Gary B. Shelly, Thomas J. Cashman and Harry J. Rosenblatt , Publisher: SHELLY CASHMAN SEWIES. [2] system analysis and design, sixth edition Authors: Kenneth E. Kendall and Julie E. Kendall Publisher: Prentice Hall [3] Modern Systems Analysis and Design Third Edition Authors: Jeffrey A. Hoffer , Joey F. George, Joseph S. Valacich Publisher: prentice hall [4] System Analysis and Design, 3rd Edition Authors: Dennis, Wixom, & Roth Publisher: John Wiley & sons Avicenna System Analysis and Design System Analysis 14