Generation data groups

A generation data group (GDG) is a chronological collection of related files. GDGs simplify the processing of multiple versions of related data.

Each file within a GDG is called a generation data set (GDS) or generation. (In this information, generation data sets are referred to as generation files. The term file on the workstation is equivalent to the term data set on the host.)

Within a GDG, the generations can have like or unlike attributes including ORGANIZATION, record format, and record length. If all generations in a group have consistent attributes and sequential organization, you can retrieve the generations together as a single file.

There are advantages to grouping related files. For example:

The generations within a GDG have sequentially ordered relative and absolute names that represent their age.

The relative name of a generation file is the group name followed by an integer in parentheses. For example, if the name of a group is hlq.PAY:
The absolute name of a generation file contains the generation number and version number. For example, if the name of a group is hlq.PAY:

For more information about forming absolute and relative names, see the related tasks.

Generation order is typically but not necessarily the same as the order in which files were added to a group. Depending on how you add generation files using absolute and relative names, you might insert a generation into an unexpected position in a group. For details, see the related reference about insertion and wrapping of generation files.

GDGs are supported in all of the COBOL for AIX file systems.

Restriction: A GDG cannot contain either an SFS indexed file that has any alternate indexes, or an SdU indexed file that requires a list of alternate indexes in the file name. The restriction is due to the ambiguity between the syntax of a parenthesized alternate index list and the syntax of GDG relative names, which also require a parenthesized expression.

For information about creating and initializing generation data groups, see the appropriate related task.

To delete, rebuild, clean up, modify, or list generation groups, or add or delete generations within a group, use the gdgmgr utility. To see a summary of gdgmgr functions, issue the following command: gdgmgr -h. For further details about the gdgmgr utility, see its man page.

related tasks  
Creating generation data groups  
Using generation data groups  

related references
Name format of generation files  
Insertion and wrapping of generation files  
Limit processing of generation data groups  
File specification