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The key must be such that it uniquely identifies a record. If more than one index is present the other ones are called alternate indexes. The indexes are created with the file and maintained by the system.
Support for indexed files is built into COBOL and PL/I. Other languages with more limited I/O facilities such as C support indexed files through add-on packages in a runtime library such as C-ISAM.
The COBOL language supports indexed files with the following command in the
FILE CONTROL section
ORGANIZATION IS INDEXED
In recent systems relational databases are often used in place of indexed files.
- Hash table
- Data set (IBM mainframe)
- Legacy system
- dbm also X/Open ndbm and GNU gdbm
- Berkeley DB
- 1 VS COBOL II Application Programming Language Reference, Release 4, Eighth Edition (March 1993), IBM Corporation, Department J58, Copyright International Business Machines Corporation 1984, 1993. pp. 67-73
- IBM Corporation (2012). Enterprise PL/I for z/OS, Version 4.3, Language Reference. p. 276. Retrieved Nov 25, 2015.
- I IBM Corporation. "Informix C-ISAM". Retrieved Nov 25, 2015.
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