[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
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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.
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► 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.
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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.
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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?
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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.
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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.
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Data flow diagramsData flow diagrams
A simple data flow diagram that shows a new video being added to a video library
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A Sample Data Flow Diagram
TimekeepingProcessPayroll
Data
Employees
Payroll Data
Payroll Data Paychecks
PayrollData
Payroll Details
Data Flow Diagramfor Payroll Processing
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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.
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System Flowchart Symbols Input/Output
Manual Input
Keying Operation
Display
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System Flowcharting Symbols Processing
Manual Operation
Processing
Collate
AuxiliaryOperation
Sorting
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System Flowcharting Symbols Storage
Punched Card
PunchedPaper Tape
MagneticTape
Input/Output
Document
MagneticDisk
Online Storage OfflineStorage
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System Flowcharting Symbols Miscellaneous
Termination
Communication Link
Data Preparation
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Systems flowchartsSystems flowcharts
A simple flowchart of a database
system
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Flow ChartsFlow Charts► This flow chart This flow chart
shows how an shows how an Internet search Internet search is conducted.is conducted.
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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
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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
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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