1. 11
Chapter 12Chapter 12
Describing InformationDescribing Information
SystemsSystems

2. 2
Describing information systemsDescribing information systems
► A system is a group of connected operations.A system is a group of connected operations.
► We can describe them in terms of inputs, processes andWe can describe them in terms of inputs, processes and
outputsoutputs
► Systems can be described in several different waysSystems can be described in several different ways
including:including:
 Structure diagrams.Structure diagrams.
 Data flow diagrams.Data flow diagrams.
 Systems flowchartsSystems flowcharts
Input Process Output

3. 3
Structure diagramsStructure diagrams
►In a structure diagram the overall task isIn a structure diagram the overall task is
broken down into smaller tasks.broken down into smaller tasks.
►These smaller tasks can, in turn, be brokenThese smaller tasks can, in turn, be broken
down into even smaller tasks.down into even smaller tasks.
►This method of describing a task is calledThis method of describing a task is called
‘The Top Down Approach’.‘The Top Down Approach’.
►It can also be shown as a simple diagram.It can also be shown as a simple diagram.

4. 4
► First we place theFirst we place the
overall task at the topoverall task at the top
and we write briefand we write brief
description of thedescription of the
overall task.overall task.
► This task is thenThis task is then
divided up into adivided up into a
series of tasksseries of tasks
required to main task.required to main task.
► Preparing a shoppingPreparing a shopping
listlist
► Do the shoppingDo the shopping
► Put the shoppingPut the shopping
away.away.

5. 5
Example of a ‘Top Down’Example of a ‘Top Down’
structurestructure
Make a
meal
Prepare
food
Set the
table
Cook the
food
The task of making a meal is broken down into smaller
tasks –
Preparing the food.
Setting the table.
Cooking the food.

6. 6
Example of a ‘Top Down’Example of a ‘Top Down’
structurestructure
Make a
meal
Prepare
food
Set the
table
Cook the
food
Could the smaller tasks be broken down into even
smaller tasks?

7. 7
Data flow diagramsData flow diagrams
► AA data-flow diagramdata-flow diagram shows the logical flows of datashows the logical flows of data
through a transaction processing system withoutthrough a transaction processing system without
regard to the time period when each occurs.regard to the time period when each occurs.
► Physical devices that transform data are not used inPhysical devices that transform data are not used in
these diagrams.these diagrams.
► In a data flow diagram the movement of data around theIn a data flow diagram the movement of data around the
system is shown.system is shown.
► This is done using standard symbols including:This is done using standard symbols including:
 Boxes.Boxes.
 Sausages or CircleSausages or Circle
 Open rectangles.Open rectangles.
 Arrows.Arrows.

8. 8
Symbols used in Data FlowSymbols used in Data Flow
DiagramsDiagrams
► AA squaresquare represents a data source or datarepresents a data source or data
destinationdestination. Such as an order form from a. Such as an order form from a
customercustomer
► A circle (or bubble or Sausage)A circle (or bubble or Sausage)
indicates a process that changes orindicates a process that changes or
transforms data.transforms data.
► AnAn open-ended rectangleopen-ended rectangle
represents a store or repository of data.represents a store or repository of data.
► AA lineline with an arrow indicates thewith an arrow indicates the
direction of thedirection of the

9. 9
Data flow diagramsData flow diagrams
A simple data flow diagram that shows a
new video being added to a video library

10. 10
A Sample Data Flow Diagram
Timekeeping
Process
Payroll
Data
Employees
Payroll Data
Payroll Data Paychecks
Payroll
Data
Payroll Details
Data Flow Diagram
for Payroll Processing

11. 11
Systems flowchartsSystems flowcharts
►A systems flowchart gives an overall viewA systems flowchart gives an overall view
of a system.of a system.
►It shows the tasks performed on the dataIt shows the tasks performed on the data
(e.g. sorting, updating) and the type of(e.g. sorting, updating) and the type of
media used to hold the data (e.g.media used to hold the data (e.g.
magnetic disk, magnetic tape).magnetic disk, magnetic tape).
►Standard symbols are used in systemsStandard symbols are used in systems
flowcharts, and data flow is indicated byflowcharts, and data flow is indicated by
arrows.arrows.

12. 12
Systems flowchartsSystems flowcharts
Magnetic
tape

13. 13
System Flowchart Symbols
Input/Output
Manual Input
Keying Operation
Display

14. 14
System Flowcharting Symbols
Processing
Manual Operation
Processing
Collate
Auxiliary
Operation
Sorting

15. 15
System Flowcharting Symbols
Storage
Punched Card
Punched
Paper Tape
Magnetic
Tape
Input/Output
Document
Magnetic
Disk
Online Storage Offline
Storage

16. 16
System Flowcharting Symbols
Miscellaneous
Termination
Communication Link
Data Preparation

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Systems flowchartsSystems flowcharts
A simple flowchart
of a database
system

18. 18
Flow ChartsFlow Charts
► This flow chartThis flow chart
shows how anshows how an
Internet search isInternet search is
conducted.conducted.

19. 19
System Flow chart for producingSystem Flow chart for producing
gas/electricity billsgas/electricity bills
Sort Program
Program producing bills
Bills Errors reports
OMR reading sheet
Validate meter reading sheet
Input using keyboard
Rejected
meter reading
Transaction file
Sorted payment
transaction file
Customer
master
file
Updated customer
master file
Bill file list

20. 20
System Flow chart for processingSystem Flow chart for processing
Payroll SystemPayroll System
Sort Program
Update Program
Final demands Remainder
Validate
Bills posted with cheques or
postal orders
Payment
Transaction file
Sorted payment
transaction file
Updated bill file
Bill file list
Details of
payments direct
from banks

21. 21

22. 22
System Flow chart for PayrollSystem Flow chart for Payroll
Sort Program
Update Program
Error reports
Validate
Program
Sorted payment
transaction file
Clock card
Error Report
Wages Slips
Calculates Wages
Transaction file
Tax tables on disk
Employee master file
Updated Master file