DL-I CALLS - IBM Mainframe

DL/I calls can be subdivided into retrieval calls, update calls, and miscellaneous calls:

Retrieval Calls

The retrieval calls are as follows:

  • GU (Get Unique) - Gets the first segment which matches the qualifiers specified in the call.
  • GN (Get Next) - Gets the next segment in hierarchical order which matches the qualifiers in the call.
  • GNP (Get Net within Parent) - Gets the next segment under the current parent which matches the qualifiers specified in the call.
  • GHU (Get Hold Unique) - Same as GU, but locks the segment for subsequent update (DLET or REPL)
  • GHN (Get Hold Next) - Same as GN, but locks the segment for subsequent update (DLET or REPL)
  • GHNP (Get Hold within Parent) - Same as GNP, but locks the segment for subsequent update (DLET or REPL)

Update Calls

The update calls are as follows:

  • ISRT - To insert a segment in the database.
  • REPL - To replace an existing segment with new data (the key of the segment cannot be changed and a previous 'Get Hold' command must be issued).
  • DUET - To delete an existing segment from the database (a previous 'Get Hold' command must be issued).

Miscellaneous Calls

The miscellaneous calls are as follows:

  • CHKP - To take a 'checkpoint' or commit updates to the database before the program terminates.
  • XRST- To restore database position after a checkpoint has been taken.
  • PCB - To schedule a PSB in an on-line program.
  • TERM - To terminate a PSB in an on-line program.

In general, DL/I acts on one statement at a time. GU and GHU are used either for random processing or to establish position in the database, while GN, GHN, GNP and GHNP are used for sequential processing.


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