1. Documenting Information Systems
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. Basic DFD Symbols

4. CONTEXT DIAGRAM

5. Physical DFD

6. Logical DFD

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. Source A
The
System B
Sink
Context Diagram

9. 2.0
Source A
1.0 C
Data Store D
3.0
Sink
The level DFD B

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

11. D
File
3.1 I
3.2 H
Diagram 3.0 B

12. D
3.1.1 I J
3.1.2
Diagram 3.1 H

13. 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

14. 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

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. 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

17. 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

18. 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

19. 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

20. 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)

21. 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

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

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. Causeway Physical DFD

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. Causeway Logical Level 0 DFD

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. 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. 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.

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. 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. 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. 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.

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.