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Table of Contents
- Sequential Access by Primary Key
- Sequential Access by Primary and Alternate Key
- Specifying the Record Number
- Specifying a Key Value
- Sequential Access by Partial Key Value
- Random Access of a Single Record
- Using a Key Value
- Using the Relative Record Number
- Using a Physical Record Number
- Sequential Access in Physical Record Order
- Shared File Access
KSAM files offer multiple record retrieval options using primary and alternate
keys, and logical and physical record numbers. The following list identifies
the methods of reading KSAM file data:
Sequential access:
Random access:
By key value. By logical record number. By approximate key match. By partial key. By physical record number.
KSAM uses two types of pointers to identify the location
of records to be read: the logical record pointer and the physical
record pointer. The logical record pointer points to a key in the
index, which points to a data record. This pointer is used to locate
records by key. The physical record pointer points directly to a
data record. This pointer is used to locate records by their physical
location in the file.
Intrinsics that use pointers are either pointer-dependent
or pointer-independent. Pointer-dependent intrinsics expect the
pointer to be positioned in order to execute correctly. Pointer-independent
intrinsics execute regardless of where the pointer is positioned.
KSAM maintains an advance flag to specify whether or not
to advance the pointers before the specific function. If the flag
is set to TRUE, pointers are advanced before performing the intrinsic
function. If the flag is set to FALSE, the intrinsic function is
performed without advancing the pointers first.
Intrinsics have been developed to position pointers and to read records in
sequence or randomly, by key value and by record number.
Table 5-1 "Pointer and Advance Flag Settings for
Reading" identifies the intrinsics used to access files and identifies
those pointers that are set by each.
Table 5-1 Pointer and Advance Flag Settings for Reading
| Intrinsic |
Reads Advance Flag |
Sets Pointer |
Sets Advance Flag |
Pointer Dependant |
| FFINDBYKEY | no | both | no | no |
| FFINDN | no | both | no | no |
| FPOINT | no | both | no | no |
| FREAD | yes | both | yes | yes |
| FREADBYKEY | no | both | no | no |
| FREADC | yes | PHYS | yes | yes |
| FREADDIR | no | PHYS | yes | no |
| FSPACE | yes | both | no | yes |
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NOTE: COBOL II and Business BASIC provide KSAM file access
routines that read records by key value. Refer to your programming
language manual for details.
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