Documenting Information Systems Chapter 3 Documenting Information Systems

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.

Basic DFD Symbols

CONTEXT DIAGRAM

Physical DFD

Logical DFD

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.

Source A The System B Sink Context Diagram

2.0 Source A 1.0 C Data Store D 3.0 Sink The level 0 DFD B

Diagram 1.0 1.2 A 1.1 E G F 1.4 1.3 C D

D File 3.1 I 3.2 H Diagram 3.0 B

D 3.1.1 I J 3.1.2 Diagram 3.1 H

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

Entity-Relationship Diagram INVENTORY ORDER N M line item 1 M N received from fills line item 1 N N CUSTOMER 1 made to N SALE

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.

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

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

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

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

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

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

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

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.

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

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.

Causeway Physical DFD

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.

Causeway Logical Level 0 DFD

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.

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.

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.

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.

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.

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.

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.

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.