File organization


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File organization

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