F command code

You can use the F command code to start the search with the first occurrence of a certain segment type or to insert a new segment as the first occurrence in a chain of segments.

Retrieving a segment as the first occurrence

You can use the F command code for GN and GNP calls. Using it with GU calls is redundant (and is disregarded) because GU calls can already back up in the database. When you use F, you indicate that you want the search to start with the first occurrence of the segment type you indicate under its parent in attempting to satisfy this level of the call.

You can use the F command code for GN and GNP calls to back up in the database. You can back up to the first occurrence of the segment type that has current position, or you can back up to a segment type that is before the current position in the hierarchy.

Restriction: The parent of the segment that you are backing up from must be in the same hierarchic path as the segment you are backing up to. IMS disregards F when you supply it at the root level or with a GU or GHU.

The search must start with the first occurrence of the segment type that you indicate under the parent. When the search at that level is satisfied, that level is treated as though a new occurrence of a segment has satisfied the search. This is true even when the segment that satisfies an SSA where F command code is specified as the same segment occurrence on which DL/I was positioned before the call was processed.

When a new segment occurrence satisfies an SSA, the position of all dependent segments is reset. New searches for dependent segments then start with the first occurrence of that segment type under its parent.

Inserting a segment as the first occurrence

When you use F with an ISRT call, you are indicating that you want IMS to insert the segment you have supplied as the first segment occurrence of its segment type. Use F with segments that have either no key at all or a non unique key, and that have HERE specified on the RULES operand of the SEGM statement in the DBD. If you specify HERE in the DBD, the F command code overrides this, and IMS inserts the new segment occurrence as the first occurrence of that segment type.

Using the F command code to override the RULES specification on the DBD applies only to the path (either logical or physical) that you are using to access the segment for the ISRT call. For example, if you are using the physical path to access the segment, the command code applies to the physical path but not to the logical path. For clarification of using command codes with the RULES specification, ask the database administrator at your installation.

For example, suppose that you specified RULES=HERE in the DBD for the TREATMNT segment. You want to satisfy this request:

Mary Martin visited the clinic today and visited a number of different doctors. Add the TREATMNT segment for Dr. Smith as the first TREATMNT segment for the most recent illness.

First you build a TREATMNT segment in your I/O area:

19930302ESEDRIXbbb0040SMITHbbbbb

Then you issue an ISRT call with the following SSA. This adds a new occurrence of the TREATMNT segment as the first occurrence of the TREATMNT segment type among those with equal keys.

ISRT    PATIENTb(PATNObbb=b06439)
        ILLNESSb*L
        TREATMNT*F

This example applies to HDAM or PHDAM root segments and to dependent segments for any type of database.