Introduction to Direct Access Files Sequential Files Adding

Sequential Files - Adding a Record Ordered Rec 001 Rec 005 Rec 045 Rec

Sequential Files - Adding a Record New-Ordered Rec 001 Rec 005 Rec 045 Rec

Sequential Files - Deleting a Record Ordered Rec 001 Rec 005 Rec 045 Rec

Sequential Files - Deleting a Record New-Ordered Rec 001 Rec 005 Rec 045 Rec

Sequential Files - Amending a Record Ordered Rec 001 Rec 005 Rec 045 Rec

Sequential Files - Amending a Record New-Ordered Rec 001 Rec 005 Rec 045 Rec

Relative Files - Organization 1 2 3 Relative Record Number 4 5 6 7

Relative Files - Adding a Record 1 2 3 Relative Record Number 4 5

Relative Files - Deleting a Record 1 2 3 Relative Record Number 4 5

Relative Files - Amending a Record 1 2 3 Relative Record Number 4 5

Indexed Files - Organization H R Z Index Records C F H L O

Indexed Files - Reading Record Ni H R Z Index Records C F H

Sequential Files. Disadvantages. u u Slow - when the hit rate is low. Complicated

Relative Files. Disadvantages. u u Wasteful of storage if the file is only partially

Indexed Files. Disadvantages. u u u Slowest Direct Access organization. Especially slow when adding

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Introduction to Direct Access Files.

Sequential Files - Adding a Record Ordered Rec 001 Rec 005 Rec 045 Rec 090 Rec 100 Rec 150 Rec 300 Rec 325 ^Z Rec 085 Unordered Rec 300 Rec 150 Rec 005 Rec 090 Rec 045 Rec 100 Rec 001 Rec 325 ^Z

Sequential Files - Adding a Record New-Ordered Rec 001 Rec 005 Rec 045 Rec 085 Rec 090 Rec 100 Rec 150 Rec 300 Rec 325 ^Z Rec 085 Extend-Unordered Rec 300 Rec 150 Rec 005 Rec 090 Rec 045 Rec 100 Rec 001 Rec 325 Rec 085 ^Z

Sequential Files - Deleting a Record Ordered Rec 001 Rec 005 Rec 045 Rec 090 Rec 100 Rec 150 Rec 300 Rec 325 ^Z Rec 150 Unordered Rec 300 Rec 150 Rec 005 Rec 090 Rec 045 Rec 100 Rec 001 Rec 325 ^Z

Sequential Files - Deleting a Record New-Ordered Rec 001 Rec 005 Rec 045 Rec 090 Rec 100 Rec 325 ^Z Rec 150 New-Unordered Rec 300 Rec 005 Rec 090 Rec 045 Rec 100 Rec 001 Rec 325 ^Z

Sequential Files - Amending a Record Ordered Rec 001 Rec 005 Rec 045 Rec 090 Rec 100 Rec 150 Rec 300 Rec 325 ^Z Rec 045 Unordered Rec 300 Rec 150 Rec 005 Rec 090 Rec 045 Rec 100 Rec 001 Rec 325 ^Z

Sequential Files - Amending a Record New-Ordered Rec 001 Rec 005 Rec 045 Rec 090 Rec 100 Rec 150 Rec 300 Rec 325 ^Z Rec 045 New-Unordered Rec 300 Rec 150 Rec 005 Rec 090 Rec 045 Rec 100 Rec 001 Rec 325 ^Z

Relative Files - Organization 1 2 3 Relative Record Number 4 5 6 7 325 326 327 328 Rec 001 free Rec 003 Rec 004 free Rec 007 Rec 325 Rec 326 free Rec 328

Relative Files - Adding a Record 1 2 3 Relative Record Number 4 5 6 7 325 326 327 328 Rec 001 free Rec 003 Rec 004 free Rec 007 Rec 325 Rec 326 free Rec 328 Rec 327

Relative Files - Adding a Record 1 2 3 Relative Record Number 4 5 6 7 325 326 327 328 Rec 001 free Rec 003 Rec 004 free Rec 007 Rec 325 Rec 326 Rec 327 Rec 328 Rec 327

Relative Files - Deleting a Record 1 2 3 Relative Record Number 4 5 6 7 325 326 327 328 Rec 001 free Rec 003 Rec 004 free Rec 007 Rec 325 Rec 326 free Rec 328 Rec 325

Relative Files - Deleting a Record 1 2 3 Relative Record Number 4 5 6 7 325 326 327 328 Rec 001 free Rec 003 Rec 004 free Rec 007 deleted/free Rec 326 free Rec 328 Rec 325

Relative Files - Amending a Record 1 2 3 Relative Record Number 4 5 6 7 325 326 327 328 Rec 001 free Rec 003 Rec 004 free Rec 007 Rec 325 Rec 326 free Rec 328 Rec 007

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

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

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

Relative Files. Disadvantages. u u 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. Advantages. u u u Fastest Direct Access organization. Very little storage overhead. Can be read sequentially.

Indexed Files. Disadvantages. u u u 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. Advantages. u u 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.