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File organization


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    • Serial
    • Sequential
    • Indexed Sequential
    • Direct Access /Random Access
  • 3. Serial File Organization
    • A collection of records
    • No particular sequence
    • Cannot be used as master
    • Used as temporary transaction file
    • Records stored in the order received
  • 4. Sequential File Organization
    • A collection of records
    • Stored in key sequence
    • Adding/deleting record requires making new file
    • Used as master files
  • 5. Sequential file
  • 6. Advantages
    • Simple file design
    • Very efficient when most of the records must be processed e.g. Payroll
    • Very efficient if the data has a natural order
    • Can be stored on inexpensive devices like magnetic tape.
  • 7. Disadvantages
    • Entire file must be processed even if a single record is to be searched.
    • Transactions have to be sorted before processing
    • Overall processing is slow
  • 8. Direct (Random) File Organization
    • Records are read directly from or written on to the file.
    • The records are stored at known address.
    • Address is calculated by applying a mathematical function to the key field.
  • 9. Direct (Random) File Organization
    • A random file would have to be stored on a direct access backing storage medium e.g. magnetic disc, CD, DVD
    • Example : Any information retrieval system. Eg Train timetable system.
  • 10. Advantages
    • Any record can be directly accessed.
    • Speed of record processing is very fast.
    • Up-to-date file because of online updating.
    • Concurrent processing is possible.
  • 11. Disadvantages
    • More complex than sequential
    • Does not fully use memory locations
    • More security and backup problems
  • 12. Indexed sequential file
    • Each record of a file has a key field which uniquely identifies that record.
    • An index consists of keys and addresses .
    • An indexed sequential file is a sequential file (i.e. sorted into order of a key field) which has an index .
    • A full index to a file is one in which there is an entry for every record.
  • 13. Indexed sequential file
  • 14. Indexed sequential file
    • Indexed sequential files are important for applications where data needs to be accessed.....
      • sequentially
      • randomly using the index.
  • 15. Indexed sequential file
    • An indexed sequential file can only be stored on a random access device e.g. magnetic disc, CD.
  • 16. Advantages
    • Provides flexibility for users who need both type of accesses with the same file
    • Faster than sequential
  • 17. Disadvantages
    • Extra storage space for the index is required
  • 18. Batch Processing
    • Batch processing is updating master files periodically to reflect all transactions that occurred during a given time period.
    • The master file is updated at set times or whenever a manageable number of transactions are gathered.
    • Transaction data can either be entered as a batch or as each transaction occurs.
  • 19. Batch Processing Master file Group source documents into batches.
  • 20. On-line Batch Processing Master file Enter transactions into system as they occur.
  • 21. On-line, Real-Time Processing
    • In on-line, real-time processing, the computer captures data electronically,...
      • edits it for accuracy and completeness, and...
      • immediately processes it.
    • The computer also processes information requests from users.
  • 22. On-line, Real-Time Processing Master file Enter transactions into system as they occur.
  • 23. Advantages of Each Method
    • The main advantage of batch processing was efficiency in processing.
    • On-line data entry is more accurate than periodic batch input because the system can refuse incomplete of erroneous entries.
    • Real-time processing ensures that the information in master files is always current.