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# Ch 12 describing information system

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### Ch 12 describing information system

1. 1. 11 Chapter 12Chapter 12 Describing InformationDescribing Information SystemsSystems
2. 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. 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.
5. 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. 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. 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. 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. 9 Data flow diagramsData flow diagrams A simple data flow diagram that shows a new video being added to a video library
10. 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. 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. 12 Systems flowchartsSystems flowcharts Magnetic tape
13. 13. 13 System Flowchart Symbols Input/Output Manual Input Keying Operation Display
14. 14. 14 System Flowcharting Symbols Processing Manual Operation Processing Collate Auxiliary Operation Sorting
15. 15. 15 System Flowcharting Symbols Storage Punched Card Punched Paper Tape Magnetic Tape Input/Output Document Magnetic Disk Online Storage Offline Storage
16. 16. 16 System Flowcharting Symbols Miscellaneous Termination Communication Link Data Preparation
17. 17. 17 Systems flowchartsSystems flowcharts A simple flowchart of a database system
18. 18. 18 Flow ChartsFlow Charts ► This flow chartThis flow chart shows how anshows how an Internet search isInternet search is conducted.conducted.
19. 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. 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. 21
22. 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