[email protected](0333-4461420) Chapter 12 Describing Information Systems.

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Chapter 12Chapter 12

Describing Information Describing Information SystemsSystems

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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 We can describe them in terms of inputs, processes

and outputsand outputs

► Systems can be described in several different ways Systems 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


Structure diagramsStructure diagrams

► In a structure diagram the overall task In a structure diagram the overall task is broken down into smaller tasks.is broken down into smaller tasks.

►These smaller tasks can, in turn, be These smaller tasks can, in turn, be broken down into even smaller tasks.broken down into even smaller tasks.

►This method of describing a task is This method of describing a task is called ‘The Top Down Approach’.called ‘The Top Down Approach’.

► It can also be shown as a simple It can also be shown as a simple diagram.diagram.


► First we place the First we place the overall task at the overall task at the top and we write top and we write brief description of brief description of the overall task.the overall task.

► This task is then This task is then divided up into a divided up into a series of tasks series of tasks required to main required to main task.task.

► Preparing a Preparing a shopping listshopping list

► Do the shopping Do the shopping ► Put the shopping Put the shopping

away.away.


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.


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?


Data flow diagramsData flow diagrams

► A A data-flow diagram data-flow diagram shows the logical flows of shows the logical flows of data through a transaction processing system data through a transaction processing system without regard to the time period when each without regard to the time period when each occurs.occurs.

► Physical devices that transform data are not used Physical devices that transform data are not used in these diagrams.in these diagrams.

► In a data flow diagram the movement of data around In a data flow diagram the movement of data around the system is shown.the 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.


Symbols used in Data Flow Symbols used in Data Flow DiagramsDiagrams

► A A square square represents a data source or data represents 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 or indicates a process that changes or transforms data.transforms data.

► An An open-ended rectangleopen-ended rectangle represents represents a store or repository of data.a store or repository of data.

► A A lineline with an arrow indicates the with an arrow indicates the direction of the direction of the flow of data.flow of data.


Data flow diagramsData flow diagrams

A simple data flow diagram that shows a new video being added to a video library


A Sample Data Flow Diagram

TimekeepingProcessPayroll

Data

Employees

Payroll Data

Payroll Data Paychecks

PayrollData

Payroll Details

Data Flow Diagramfor Payroll Processing


Systems flowchartsSystems flowcharts

►A systems flowchart gives an overall A systems flowchart gives an overall view of a system.view of a system.

► It shows the tasks performed on the It shows the tasks performed on the data (e.g. sorting, updating) and the data (e.g. sorting, updating) and the type of media used to hold the data type of media used to hold the data (e.g. magnetic disk, magnetic tape).(e.g. magnetic disk, magnetic tape).

►Standard symbols are used in Standard symbols are used in systems flowcharts, and data flow is systems flowcharts, and data flow is indicated by arrows.indicated by arrows.



Magnetic tape


System Flowchart Symbols Input/Output

Manual Input

Keying Operation

Display


System Flowcharting Symbols Processing

Manual Operation

Processing

Collate

AuxiliaryOperation

Sorting


System Flowcharting Symbols Storage

Punched Card

PunchedPaper Tape

MagneticTape

Input/Output

Document

MagneticDisk

Online Storage OfflineStorage


System Flowcharting Symbols Miscellaneous

Termination

Communication Link

Data Preparation



A simple flowchart of a database

system


Flow ChartsFlow Charts► This flow chart This flow chart

shows how an shows how an Internet search Internet search is conducted.is conducted.


System Flow chart for producing System Flow chart for producing gas/electricity bills gas/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


System Flow chart for System Flow chart for processing Payroll Systemprocessing Payroll 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


System Flow chart for Payroll System 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

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