Introduction to Direct Access Files.
Sequential Files - Adding a Record Rec085 Rec300Rec150Rec005Rec090Rec045Rec100Rec001Rec325^Z Ordered Rec001Rec005Rec045Rec090Rec100Rec150Rec300Rec325^Z Unordered
Rec085 Rec300Rec150Rec005Rec090Rec045Rec100Rec001Rec325Rec085^Z New-Ordered Rec001Rec005Rec045Rec085Rec090Rec100Rec150Rec300Rec325^Z Extend-Unordered
Sequential Files - Deleting a Record Rec150 Rec300Rec150Rec005Rec090Rec045Rec100Rec001Rec325^Z Ordered Rec001Rec005Rec045Rec090Rec100Rec150Rec300Rec325^Z Unordered
Rec150 Rec300Rec005Rec090Rec045Rec100Rec001Rec325^Z New-Ordered Rec001Rec005Rec045Rec090Rec100Rec300Rec325^Z New-Unordered
Sequential Files - Amending a Record Rec045 Rec300Rec150Rec005Rec090Rec045Rec100Rec001Rec325^Z Ordered Rec001Rec005Rec045Rec090Rec100Rec150Rec300Rec325^Z Unordered
Rec045 Rec300Rec150Rec005Rec090Rec045Rec100Rec001Rec325^Z New-Ordered Rec001Rec005Rec045Rec090Rec100Rec150Rec300Rec325^Z New-Unordered
Relative Files - Organization Rec001freeRec003Rec004freefreeRec007Rec325Rec326freeRec Relative Record Number
Relative Files - Adding a Record Rec001freeRec003Rec004freefreeRec007Rec325Rec326freeRec Relative Record Number Rec327
Relative Files - Adding a Record Rec001freeRec003Rec004freefreeRec007Rec325Rec326Rec327Rec Relative Record Number Rec327
Relative Files - Deleting a Record Rec001freeRec003Rec004freefreeRec007Rec325Rec326freeRec Relative Record Number Rec325
Relative Files - Deleting a Record Rec001freeRec003Rec004freefreeRec007deleted/freeRec326freeRec Relative Record Number Rec325
Relative Files - Amending a Record Rec001freeRec003Rec004freefreeRec007Rec325Rec326freeRec Relative Record Number Rec007
Relative Files - Amending a Record Rec001freeRec003Rec004freefreeRec007Rec325Rec326freeRec Relative Record Number Rec007
Indexed Files - Organization H R Z L O R C F H T W Z Mi Nf Ni Nt Oi Ot Index Records Data Records
Indexed Files - Reading Record Ni H R Z L O R C F H T W Z Mi Nf Ni Nt Oi Ot Index Records Data Records
Indexed Files - Reading Record Ni H R Z L O R C F H T W Z Mi Nf Ni Nt Oi Ot Index Records Data Records
Indexed Files - Reading Record Ni H R Z L O R C F H T W Z Mi Nf Ni Nt Oi Ot Index Records Data Records
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.
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 little storage overhead. Can be read sequentially. Disadvantages. Advantages.
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.