COMMAND CODES - IBM Mainframe

Command codes are optional codes, which are embedded in SSAs to alter the normal way in which IMS process a call. Command codes are as follows:

  • C (Concatenated key) - Allows you to define the access path to the desired segment in a single SSA, with the keys to segments along the path concatenated into one large key.
  • D (Path call) - Allows more than one segment along the access path to be retrieved or updated at once. (Ordinarily, only the lowest-level segment in the path is retrieved.). A 'D' must be placed in the SSA of every segment in the path you wish to retrieve. The results are placed in one concatenated I/O area.
  • F (First) - Locates the first segment that satisfies the SSA. (This code is significant only for ON processing, since a GU behaves this way normally.)
  • L (Last) - Forces IMS to fond the last segment which satisfies the SSA.
  • N - Indicates which segments you retrieve with a path call you don't want IMS to replace.
  • Q - Locks a segment for your program's exclusive use.
  • U - Specifies that current database position at that level is not allowed to be changed by the call.
  • V - Specifies that current database position at that level and all levels above are not allowed to be changed by the call.
  • "Null" (Command code) - Used as a placeholder in SSAs so that command codes can be inserted or removed from SSAs without having to define separate SSAs in working storage.

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