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Introduction to Direct Access Files.

Introduction to Direct Access Files. Sequential Files - Adding a Record. Ordered. Rec085. Unordered. Rec001 Rec005 Rec045 Rec090 Rec100 Rec150 Rec300 Rec325 ^Z. Rec300 Rec150 Rec005 Rec090 Rec045 Rec100 Rec001 Rec325 ^Z. Sequential Files - Adding a Record. New-Ordered.

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Introduction to Direct Access Files.

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  1. Introduction toDirect AccessFiles.

  2. Sequential Files - Adding a Record Ordered Rec085 Unordered Rec001 Rec005 Rec045 Rec090 Rec100 Rec150 Rec300 Rec325 ^Z Rec300 Rec150 Rec005 Rec090 Rec045 Rec100 Rec001 Rec325 ^Z

  3. Sequential Files - Adding a Record New-Ordered Rec085 Extend-Unordered Rec001 Rec005 Rec045 Rec085 Rec090 Rec100 Rec150 Rec300 Rec325 ^Z Rec300 Rec150 Rec005 Rec090 Rec045 Rec100 Rec001 Rec325 Rec085 ^Z

  4. Sequential Files - Deleting a Record Ordered Rec150 Unordered Rec001 Rec005 Rec045 Rec090 Rec100 Rec150 Rec300 Rec325 ^Z Rec300 Rec150 Rec005 Rec090 Rec045 Rec100 Rec001 Rec325 ^Z

  5. Sequential Files - Deleting a Record New-Ordered Rec150 New-Unordered Rec001 Rec005 Rec045 Rec090 Rec100 Rec300 Rec325 ^Z Rec300 Rec005 Rec090 Rec045 Rec100 Rec001 Rec325 ^Z

  6. Sequential Files - Amending a Record Ordered Rec045 Unordered Rec001 Rec005 Rec045 Rec090 Rec100 Rec150 Rec300 Rec325 ^Z Rec300 Rec150 Rec005 Rec090 Rec045 Rec100 Rec001 Rec325 ^Z

  7. Sequential Files - Amending a Record New-Ordered Rec045 New-Unordered Rec001 Rec005 Rec045 Rec090 Rec100 Rec150 Rec300 Rec325 ^Z Rec300 Rec150 Rec005 Rec090 Rec045 Rec100 Rec001 Rec325 ^Z

  8. Relative Files - Organization Rec001 free Rec003 Rec004 free free Rec007 Rec325 Rec326 free Rec328 1 2 3 4 5 6 7 325 326 327 328 Relative RecordNumber

  9. Relative Files - Adding a Record Rec001 free Rec003 Rec004 free free Rec007 Rec325 Rec326 free Rec328 1 2 3 4 5 6 7 325 326 327 328 Rec327 Relative RecordNumber

  10. Relative Files - Adding a Record Rec001 free Rec003 Rec004 free free Rec007 Rec325 Rec326 Rec327 Rec328 1 2 3 4 5 6 7 325 326 327 328 Rec327 Relative RecordNumber

  11. Relative Files - Deleting a Record Rec001 free Rec003 Rec004 free free Rec007 Rec325 Rec326 free Rec328 1 2 3 4 5 6 7 325 326 327 328 Rec325 Relative RecordNumber

  12. Relative Files - Deleting a Record Rec001 free Rec003 Rec004 free free Rec007 deleted/free Rec326 free Rec328 1 2 3 4 5 6 7 325 326 327 328 Rec325 Relative RecordNumber

  13. Relative Files - Amending a Record Rec001 free Rec003 Rec004 free free Rec007 Rec325 Rec326 free Rec328 1 2 3 4 5 6 7 325 326 327 328 Rec007 Relative RecordNumber

  14. Relative Files - Amending a Record Rec001 free Rec003 Rec004 free free Rec007 Rec325 Rec326 free Rec328 1 2 3 4 5 6 7 325 326 327 328 Rec007 Relative RecordNumber

  15. Indexed Files - Organization H R Z Index Records C F H L O R T W Z Mi Nf Ni Nt Oi Ot Data Records

  16. Indexed Files - Reading Record Ni H R Z Index Records C F H L O R T W Z Mi Nf Ni Nt Oi Ot Data Records

  17. Indexed Files - Reading Record Ni H R Z Index Records C F H L O R T W Z Mi Nf Ni Nt Oi Ot Data Records

  18. Indexed Files - Reading Record Ni H R Z Index Records C F H L O R T W Z Mi Nf Ni Nt Oi Ot Data Records

  19. Sequential Files. • Slow - when the hit rate is low. • Complicated to change (insert, delete, amend) • Fast - when the hit rate is high. • Most storage efficient. • Simple organization. • Recovers space from deleted records. Disadvantages. Advantages.

  20. Relative Files. • Wasteful of storage if the file is only partially populated. • Cannot recover space from deleted records. • Only a single, numeric key allowed. • Keys must map on to the range of the Relative Record numbers. • Fastest Direct Access organization. • Very littlestorage overhead. • Can be read sequentially. Disadvantages. Advantages.

  21. Indexed Files. • Slowest Direct Access organization. • Especially slow when adding or deleting records. • Not very storage efficient. Must store the Index records, the alternate Index records, the data records and the alternate data records. • Can use multiple, alphanumeric keys. • Can have duplicate alternate keys. • Can be read sequentially on any of its keys. • Can partially recover space from deleted records. Disadvantages. Advantages.

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