System Analysis Mr Ahmad AlGhoul Learning Objectives n
System Analysis - Mr. Ahmad Al-Ghoul
Learning Objectives n n n Discuss how to create a set of data flow diagrams in a sequence, from general to specific discuss and draw the context diagram Discuss and draw a Diagram 0 Avicenna System Analysis and Design System Analysis 2
Creating a Set of DFDs n n Create a graphical model of the information system based on your fact-finding results Create a set of DFDs by performing three main tasks n n Step 1: Draw a context diagram, including all external entities and the major data flow to or from them Step 2: Draw a diagram 0 DFD by analyzing the major activities within the context process n n Avicenna Include the external entities and major data stores Step 3: Draw the lower-level diagrams for each complex process on Diagram 0 System Analysis and Design System Analysis 3
Creating a Set of DFDs n The procedure for producing a DFD is to: n n n n n Avicenna identify and list external entities providing inputs to the system and receiving outputs from system identify and list inputs from external entities and outputs to external entities create a context diagram with system at center and external entities sending and receiving data flows identify the processes included within the system boundary identify the data connections between processes verify all data flows have a source and destination verify data coming out of a data store goes as input to a process review with "informed" explode and repeat above steps as needed System Analysis and Design System Analysis 4
Creating a Set of DFDs n Draw a Context Diagram n n n n Avicenna Context Diagram is going to be the simplest DFD ( will have the minimum amount of symbols) First DFD in every business process Shows the context into which the business process fits Contains only one process, representing the entire system The process is given the number zero All external entities are shown on the context diagram as well as major data flow to and from them The diagram does not contain any data stores System Analysis and Design System Analysis 5
Creating a Set of DFDs n Draw a Context Diagram Begin by reviewing the system requirements to identify all external data sources and destinations n Record the name of the entities and the name and content of the data flows, and the direction of the data flows n Avicenna System Analysis and Design System Analysis 6
Creating a Set of DFDs n We will use example of information system, the example is an order system that a company uses to enter orders and apply payments against a customer's balance n External entities are n n n Order information system consist of three main processes n n n Avicenna CUSTOMER WAREHOUSE SALES REP BANK ACCOUNTING FILL ORDER: which contains three sub processes, VERIFY ORDER, PREPARE REJECT NOTICE, and ASSEMBLE ORDER CREATE INVOICE: no sub process APPLY PAYMENT: which contains four sub processes POST PAYMENT, DEPOSIT PAYMENT, PREPARE ACCOUNTING ENTRY, and PAY COMMISSION System Analysis and Design System Analysis 7
Creating a Set of DFDs Context diagram DFD for an order system. n Notice that the ORDER SYSTEM process is at the center of diagram and five entities surround the process n Three of the entities, SALES REP, BANK, and ACCOUNTING, have a single incoming data flows for COMMISSION, BANK DEPOSIT, and CASH RECEEIPTS n The WAREHOUSE entity has one incoming data flow PICKING LIST that is a report, that shows the items and their quantity, location, and sequence. The WAREHOUSE entity has one outgoing data flow, COMPLETED ORDER n The CUSTMER entity has two outgoing data flows, ORDER and PAYMENT, and two incoming data flows, ORDER REJECT NOTICE and INVOICE [1] Avicenna System Analysis and Design System Analysis 8
Creating a Set of DFDs n Draw a Diagram 0 DFD n n Avicenna The Context Diagram is a good starting point but it does not tell us much about the system, and that is where low level DFDs come into play. In Context Diagram we had only one Process, we will break up this process into sub-processes. The Diagram that will result from this breaking-up is called Diagram 0 (named so, because we are drawing a DFD that further explains the Process number "0"). How many sub-processes should we make out of Process 0? There is no rule It all depends on the system System Analysis and Design System Analysis 9
Creating a Set of DFDs n Draw a Diagram 0 DFD n n n n Avicenna Diagram 0 is the explosion of the context level diagram Processes are numbered with an integer The process numbers do not suggest that the processes are accomplished in a sequential order Each process always is considered to be available, active, and awaiting data to be processed The major data stores and all external entities are included on Diagram 0 A diverging data flow is a data flow in which the same data travels to two or more different locations If same data flows in both directions, you can use a double-headed arrow To identify specific data flows into and out of a symbol, however, you use separate data flows symbols with single arrowheads System Analysis and Design System Analysis 10
Creating a Set of DFDs n Draw a Diagram 0 DFD n n If more detail were needed for any process in diagram 0, you would draw a level 1 diagrams If more detail needed for any process in level 1 diagrams , you would draw a level 2 diagrams, and so on n Parent diagram n n Child diagram n n n Avicenna The lower level diagram Functional primitive n n The higher level diagram Processes that do not create a child diagram You document the logic for a functional primitive in a process description in the data dictionary Later, when the logical design is implemented as a physical system, programmers will transform each functional primitive into a unit of program code that carries out the required processing steps. System Analysis and Design System Analysis 11
Creating a Set of DFDs diagram 0 for an order system. Notice that process 0 on the order system’s context diagram is exploded to show three processes, FILL ORDER, CREATE INVOICE, and APPLY PAYMENT one data store, ACCOUNTS RECEIVABLE two new data flows, INVOICE DETAIL and PAYMENT DETAIL One diverging data flow INVOICE n Depending on the processing logic n A CUSTOMER submit an ORDER, the FILL ORDER process either sends ORDER REJECT NOTICE to the customer entity or sends PICKING LIST to the WAREHOUSE entity n A COMPLETED ORDER from the WAREHOUSE entity is input to the CREATE INVOICE process, which output INVOICE to both CUSTOMER entity and the ACCOUNTS RECEIVABLE data store n PAYMENT processed by APPLY PAYMENT process requires INVOICE DETAIL from ACCOUNTS RECEIVABLE data store a long with the PAYMENT. APPLY PAYMENT process outputs PAYMENT DETAIL to the ACCOUNTS RECEIVABLE data store and outputs COMMISSION to the SALES DEPT entity, BANK DEPOSIT to the BANK entity, and CASH REEIPTS ENTRY to ACCOUNTING entity Avicenna System Analysis and Design System Analysis [1] 12
Creating a Set of DFDs n Drawing Guidelines 1. 2. 3. 4. 5. 6. Avicenna Draw the context diagram so that it fits on one page Use the name of the information system as the process name in the context diagram Use unique names within each set of symbols Do not cross lines Provide a unique name and reference number for each process Obtain user input and feedback System Analysis and Design System Analysis 13
Sequence Summary n n n A set of DFDs is like a pyramid with the context diagram at the top The context diagram represents the information system’s scope and its external connections but not its internal working Diagram 0 displays the information system’s major processes, data stores, and data flows and its exploded version of the context diagram’s process symbol, which represents the entire information system Avicenna System Analysis and Design System Analysis 14
Sequence Summary n In this Sequence we have Discuss how to create a set of data flow diagrams in a sequence, from general to specific n explained the context diagram n Explained the steps needed to draw the context diagram n Explained a Diagram 0 n n Avicenna Explained how to draw a diagram 0 System Analysis and Design System Analysis 15
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, 3 rd Edition Authors: Dennis, Wixom, & Roth Publisher: John Wiley & sons Avicenna System Analysis and Design System Analysis 16
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