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Chapter 3 Documenting Information Systems. Learning Objectives To read and evaluate data flow diagrams To read and evaluate system flowcharts. To read.

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Presentation on theme: "Chapter 3 Documenting Information Systems. Learning Objectives To read and evaluate data flow diagrams To read and evaluate system flowcharts. To read."— Presentation transcript:

1 Chapter 3 Documenting Information Systems

2 Learning Objectives To read and evaluate data flow diagrams To read and evaluate system flowcharts. To read and evaluate entity-relationship diagrams. To prepare data flow diagrams from a narrative. To prepare system flowcharts from a narrative.

3 3 Basic DFD Symbols

4 4 CONTEXT DIAGRAM

5 5 Physical DFD

6 6 Logical DFD

7 7 Balanced DFDs The next five slides depict “balanced” data flow diagrams. Balanced DFDs exist when the external data flows are equivalent. The first DFD is a context diagram and the next one is an “explosion” of it into a level 0 logical DFD. The next diagram is an “explosion” of the logical level 0 DFD, and so on.

8 8 Source The System Sink A B Context Diagram

9 9 Source Sink The level 0 DFD Data Store A C D B

10 G E C A D F Diagram 1.0

11 H D I B File Diagram 3.0

12 D J I H Diagram 3.1

13 13 Standard Flowchart Symbols INPUTSPROCESSINGOUTPUTDATA STORESCONNECTORS MISCELLANEOUS DOCUMENTS MANUAL KEYING PUNCH CARD COMPUTER PROCESS MANUAL PROCESS OFFLINE PROCESS CRT DISPLAY GENERAL PURPOSE INPUT- OUTPUT DISK TAPE PAPER FILING SEQUENCE: A = ALPHABETICAL C = CHRONOLOGICAL N = NUMERICAL START/STOP ON-PAGE CONNECTOR OFF-PAGE CONNECTOR LOGIC FLOW TELECOMMUNICATIONS LINK ANNOTATIONS BATCH TOTAL GOODS; I.e. inventory shipment

14 14 ORDER CUSTOMER SALE INVENTORY made to received from line item Entity-Relationship Diagram M M N N NN N fills

15 15 Common system flowcharting routines The following slides show several common ways of showing processing using system flowcharting. Pay particular attention to the way the columns are set up to communicate the flow of activities between processing entities.

16 16 Record input Input document Data store1 Data store 2 CLERK COMPUTER Enter document into computer via keyboard, edit input, record input Edit/validate input Key input Display input or error Resolve errors, if any Key corrections; accept input Accepted input Input document

17 17 Query input Process query Display UserComputer Update Computer User queries the computer Update sequential data store Data store(s) Input data Old master data New master data

18 18 USERCOMPUTER Document Prepare batch totals Batch totals Key document Accepted input Document N Record input Transaction data Prepare exception and summary report Exception and summary report (Implies manual reconciliation of batch totals) PREPARATION AND LATER MANUAL RECONCILIATION OF CONTROL TOTALS

19 19 DATA ENTRY CLERK 1NETWORKED PCsDATA ENTRY CLERK 2 Documents Key enter Rekey inputs Verified input Accepted inputs Record input Verify inputs Input data Documents A A KEY AND KEY VERIFY INPUTS

20 20 Scanning clerk Computer Enter document into computer using a scanner Input document Scan document Update data Data store(s)

21 21 Input document Scan document Record image Input image Display image of document Record data Document image Key data Scanning ClerkComputerData Entry Clerk Enter document into computer using scanner & manual keying

22 22 Preparing Data Flow Diagrams Read narrative carefully - number lines and paragraphs in text Prepare table of entities and activities Draw context diagram - use DFD guidelines

23 23 DFD Guidelines 1. Include within the system context (bubble) any entity that performs one or more information processing activities. 2. For now, include only normal processing routines, not exception routines or error routines, on context diagrams, physical DFDs, and logical level 0 DFDs. 3. Include on the systems documentation all (and only) activities and entities described in the systems narrative - no more, no less. 4. When multiple entities operate identically, depict only one to represent all.

24 24 Causeway Context Diagram Charge customer Bank General ledger office Cash receipts on account system Payment Deposit Cash receipts total

25 25 DFD Guidelines (cont.) 5. For clarity, draw a data flow for each flow into and out of a file. You may, also for clarity and to help you determine that you have included all necessary flows, label each flow with the activity number that gives rise to the flow or with a description of the flow. 6. If a file is logically necessary (that is, because of a delay between processes), include a file in the diagrams, whether or not it is mentioned in the narrative.

26 26 Causeway Physical DFD

27 27 DFD Guidelines (cont.) 7. Group activities if they occur in the same place and at the same time. 8. Group activities if they occur at the same time but in different places. 9. Group activities that seem to be logically related. 10. To make the DFD readable, use between five and seven bubbles.

28 28 Causeway Logical Level 0 DFD

29 29 DFD Guidelines (cont,) 11. A data flow should go to an operations entity square when only operations functions (that is, work- related functions such as storing goods, picking goods from shelves, etc.) are to performed by that entity. A data flow should enter an entity bubble if the operations entity is to perform an information processing activity. 12. On a physical DFD, reading computer data stores & writing to computer data stores must go through a computer bubble. 13. On a logical DFD, data flows cannot go from higher- to lower-numbered bubbles.

30 30 System flowcharting guidelines 1. Divide the flowchart into columns; one column for each internal entity and one for each external entity. Label each column. 2. Flowchart columns should be laid out so that the flowchart activities flow from left to right, but you should locate columns so as to minimize crossed lines and connectors.

31 31 System flowcharting guidelines (cont.) 3. Flowchart logic should flow from top to bottom and from left to right. For clarity, put arrows on all flow lines. 4. Keep the flowchart on one page. If you can’t, use multiple pages and connect the pages with off-page connectors. Do not glue, tape, staple, or otherwise extend your flowchart to get it one one page.

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33 33 System flowcharting guidelines (cont.) 5. Within each column, there must be at least one manual process, keying operation, or data store between documents. That is, do not directly connect documents within the same column. 6. When crossing organizational lines (one column to another), show a document at both ends of the flow line unless the connection is so short that the intent is unambiguous.

34 34 System flowcharting guidelines (cont.) 7. Documents or reports printed in data processing (DP) should be shown in the DP column first. You can then show the document or report going to the destination unit. 8. Documents or reports printed by a centralized computer facility on equipment located in another organizational unit ( warehouse, shipping dept.) should not be shown within the computer facility.

35 35 System flowcharting guidelines (cont.) 9. Processing within an organizational unit on devices such as a PC or computerized cash register should be shown within the unit or as a separate column next to that unit, but not in the central computer facility column. 10. Sequential processing steps (computerized or manual) with no delay between them can be shown as one process or as a sequence of processes.

36 36 System flowcharting guidelines (cont.) 11. The only way into a computer data storage unit is through a computer processing rectangle. 12. A manual process is not needed to show the sending of a document. The sending of the document should be apparent from the movement of the document itself. 13. Do not use a manual process to file a document. Just show the document going in to a file.

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38 Learning Objectives To read and evaluate data flow diagrams To read and evaluate system flowcharts. To read and evaluate entity-relationship diagrams. To prepare data flow diagrams from a narrative. To prepare system flowcharts from a narrative.


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