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IMS Database Updates

Following function codes are used for database updations.

  1. ISRT - Inserting a segment

    The ISRT call is used to add a segment occurrence to a database. It can be used either for loading a new database or for inserting a segment into an existing database.

  2. DLET - Deleting a segment

    The DLET call is used to delete a segment occurrence from the database. This has to be preceded by a successful Get-Hold call.

  3. REPL - Replacing a segment

    The REPL call is used to update the segment occurrence of the database. This has to be preceded by a successful Get-Hold call.

General Rules to be followed for DLET and REPL Calls:

There are four general rules, needs to be followed before deleting or replacing any segment occurrence. They are.

  1. The DLET or REPL call needs to be preceded by Get-Hold call, which brings the segment occurrence into the I/O area and also causes IMS to save information about the segment.

  2. No other calls are allowed that reference the same PCB, in between the Get-Hold call and Delete or modify call.

  3. No SSAs to be included, when issuing a call with the DLET or REPL function code. The only exception to this rule is a delete or replace call following a get-hold call that specifies one or more SSAs using the D command code. The D command code causes more than one segment to be brought into the I/O area with a single call.

  4. The program is not allowed to modify the key field of the segment image in the I/O area.

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