Df dpayroll2


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Df dpayroll2

  1. 1. Zicklin School of Business, Baruch College, City University of New York CIS 4800 – Systems Analysis and Design Spring 2002, Prof. R. Benbunan-Fich System Architect ® Quick Guide to DFD Start the System Architect® program, by going through Start | Programs | System Architect Student Edition | System Architect 2001. The SA 2001 window is divided in three parts. The upper left corner is the browse window, the lower left corner is the browse detail and the right side is the drawing workspace. The browse window is organized in tab sheets. The All Methods (All) sheet is displayed by default in the browse window. This tutorial assumes that you have some basic familiarity with the SA 2001 software, toolbar and features. The objective of this guide is to help you draw a set of Data Flow Diagrams (context level, level-0 and level-1) and show you how to check their completeness and correctness. Part I: Drawing a Context DFD We will start by drawing the Context Diagram shown in Figure 1. Payroll Check Employee 0 Payroll Time Sheet System Payroll Report Tax Form Accounting Department Figure 1. Payroll System Context Diagram In the File menu, click on New Diagram and then double-click on Data Flow Gane & Sarson. In the New Diagram dialog box, name the diagram DFD Payroll Context and click the OK button. Step 1: Drawing a process. Click on the Process icon on the drawing toolbar. The cursor gets a pen-shape when placed in the drawing area. Position the pen-shape cursor in the middle of the drawing area and click once. Press Enter to accept the process symbol you have just drawn.
  2. 2. Right click on the symbol, select Edit… and enter the name and the number of your process. Type the name Payroll System in the name window of the Model Object dialog box. Then select the symbol tab and enter the number of the process. Since this is a context diagram you should enter 0 as the number for the process. Click the OK button when done. Click on the Select Mode icon (leftmost arrow) on the drawing toolbar to get back the standard cursor. Step 2: Drawing External Entities Click on the External Entity icon on the drawing toolbar. Position the pen-shape cursor to the left of the process and click once. Press Enter to accept the External Entity. Right click on this symbol and select Edit… from the pop-up menu. Name your external entity Employee (you can leave the description area empty). Click OK when done. Repeat these steps to generate another External Entity to the right of the Payroll System process and name it Accounting Department. Step 3: Drawing Data Flows 1. Click on the Data Flow icon on the drawing toolbar. To draw the “time sheet” data flow, click once on the origin of the data flow (External Entity Employee) and drag the cursor to the destination of the data flow (Payroll System Process). Release the cursor on the destination of the data flow to draw the arrow. 2. Press Enter to accept the symbol you have just drawn. The Associative Properties dialog box will appear. Check that the boxes To and From contain the correct origin and destination of the data flow. If one of these boxes is empty, the data flow will not be properly associated with the other symbols of the diagram. Click OK to close the dialog box, even if the associations are not correct. If one of the associations is missing, get the standard cursor back and re-attach the loose end to the corresponding symbol. To make sure that the attachment has succeeded, right click on the arrow and select Associative… from the pop-up menu. 3. Right click on the name of the data flow and select Edit… from the pop-up menu. Name the data flow Time Sheet. Instead of Edit… you can select Symbol Rename and enter the name of your data flow. Repeat the three-steps described above to draw the remaining data flows of the context diagram. If you like to reshape any data flow (e.g. reduce the number of corners), use the standard cursor and click once on the arrow you want to modify. Drag the corners (small black squares) until you achieve the desired shape for the line. Step 4: Saving your Context Diagram You can save your work by pressing CTRL+S or by going through the File menu, Save Diagram option. In either case, click on Yes when asked to confirm.
  3. 3. Part II: Drawing a Level 0 Data Flow Diagram Now we will draw the Level 0 diagram of the Payroll system (see Figure 2). Employee 1 2 Create Compute Time Sheet Weekly Hrs. Worked Weekly Payroll Paycheck Record Payroll Paycheck Paycheck Data 3 Accounting Deduction Data Department Prepare Payroll report Payroll Summary Tax Form 4 Prepare Employee Tax Form Erroneous Data Flow Figure 2. Level 0 Data Flow Diagram Please note that the Diagram presented in Figure 2 has two mistakes. The Data Flow labeled “Hrs. Worked” is pointing in the wrong direction and there is an extra arrow (labeled “Erroneous Data Flow” connecting two external entities). In this tutorial, you will learn how to detect and correct these mistakes. Step 1: Attaching a child diagram to its parent. Start System Architect®, click on the plus sign (+) next to Diagrams in the browser window and click on the plus sign (+) next to Data Flow Gane & Sarson. Double click on DFD Payroll Context to open the diagram in the drawing window. Select the process “Payroll System” by clicking on it once. Right click and select Child Create from the pop-up menu. Name the system “Payroll System Level 0” and click OK. The Leveling Data dialog box will appear, with the following message:
  4. 4. In the child diagram, which of the following materials should be included? Image of parent symbol Line/flows attached to parent Symbols attached to lines/flows These three options will be checked by default. Unselect the first option (Image of parent symbol) and leave the last two options checked. Click OK to accept. The drawing area will show the external entities and their ingoing and outgoing data flows. Using the techniques learned in the first part of this tutorial, draw the diagram presented in Figure 2, as shown. If the Image is too small you can select Actual Size from the View menu or Zoom. To re-route the lines from the existing data flows, click on each data flow to select and choose Route Line from the pop up menu. Then, select Assign connections and reconnect the data flow to the appropriate symbol, by dragging the end of the line you want to reconnect. Save your work when finished, by pressing CTRL+S and confirm by clicking on YES when prompted. Step 2: Checking the correctness of your diagram. To check if your diagram is correct, select Rules Check from the Report Menu in the menu bar. A dialog box will appear with the following message Since the Report option did not contain a Rules Check report specification, the default specification will be used. Click OK to accept the default specification as the basis for checking the correctness of your diagram. SA 2001 will check your diagram and will issue the following report in a separate window. Rules Check Enter project name SA/2001 Educational Version Diagram Type Diagram Name Symbol Type Symbol Name Rules Data Flow Gane & Sarson Payroll System Level 0 Data Flow Erroneous Data Flow R2 - Not defined. R8 - No process at either connection. Process Compute Weekly Paycheck R9 - No input flow. Process Create Weekly Payroll Record R10 - No output flow. as of 2/11/02 Page 1 SA/2001 Educational Version
  5. 5. For each error, the report gives the rule number, a brief explanation of the violation and the name and type of the symbol in the error. The report can be printed if desired. To print the report, right click on it. From the Floating Menu, select Print. (You can also use the Print icon or File| Print.) The Rules Check option also flags the errors directly on the diagram, with a circle next to the symbol and a rule number. Let us examine and correct each one of the errors highlighted in the report. 1. As expected, the Data Flow labeled “Erroneous Data Flow” is incorrect because it does not originate or terminate in a process. Follow the instructions below to delete this Data Flow. 2. Due to the wrong direction of the “Hrs. Worked” data flow, the process “Compute Weekly Paycheck” has no input flow and the process “Create Weekly Payroll Record” has no output flow. Delete this data flow, following the instructions given below, and redraw it in the right direction. To erase the visible error indicators from the diagram, use the Clear Errors command (last option) in the Reports Menu. Step 3: Deleting a symbol from a diagram In order to erase a symbol from a diagram, it is not enough to simply delete it from the graph. The underlying definition of the symbol must also be removed. Let us examine the definitions of the symbols we have created first. 1. Click on the [Struct] tab on the browse window and then click on the plus sign next to Definitions. There will be four categories of definitions (Data Element, Data Flow, Data Store, External and Process). If you click on the plus sign next to each, you will see the names of the elements you have drawn in your diagram. This is a good opportunity to check that there are no duplications or erroneous names in each category. 2. In order to delete the “Hrs. Worked” data flow that incorrectly points to the first process (in Figure 2), highlight its name in the Data Flow definition list in the browser, right click and select the Delete option. Click Yes in the deletion option dialog box. The definition will be removed from the list. To delete the symbol from the diagram, click on it once and choose the delete option from Edit in the menu bar. When you have made all the corrections, save your changes.
  6. 6. It is recommended that your run the Rules Check report again to make sure that you have corrected all the errors. You should get a message indicating that the report is empty when your diagram is correct. Part III: Drawing a Level 1 Data Flow Diagram Now we will draw the Level 1 for process 2 in the Payroll system (see Figure 3). 2.1 Gross 2.2 2.3 Pay Net Pay Hrs. Worked Data Data Compute Compute Create Gross Pay Net Pay Payroll Check Payroll Payroll Paycheck Check Data Paycheck Data S1 Payroll Data File Figure 3. Level 1 Data Flow Diagram In order to start creating this diagram, you should have the Level-0 diagram in the drawing area. Select process 2 (Compute Weekly Paycheck) in the Level 0 Diagram, right click to get to the context sensitive menu and choose the option Child Create… Press OK in the Child Create dialog box to create a Gane & Sarson Data Flow Diagram. In the Leveling Data dialog box, unselect the first and the third option, and leave a check mark in the option line/flows attached to parent. Draw the three processes as described in Part I. Name each process as shown in the figure, and number each one with the extensions only (e.g. 1, 2, 3, etc). Then draw a Data Store, following these steps: Select the data store symbol from the toolbar; the cursor will get a pen-shape. Click on the area of the diagram where you want to draw the symbol. Hit enter to accept and right click to get the Edit menu. Enter the name of the data store (Payroll Data File) and click OK. Draw the new data flows and reassign the existing ones as described in Part II. Save your diagram when finished.