GDG(Traning Materials for EDS Company)

APPLICATION OF GENERATION DATA GROUPS A Generation Data Group, often-abbreviated GDG, is a facility of the operating system that keeps tr...

APPLICATION OF GENERATION DATA GROUPS

A Generation Data Group, often-abbreviated GDG, is a facility of the operating system that
keeps track of periodic or cyclical data sets.  As the name suggests, each new data set that
is created forms a new "generation" in a series.  Generation data groups typically follow
this pattern:

         1. A new generation of the data set is added.
         2. Some number of the previous generations of the data set is retained.
         3. The oldest generation of the data set is deleted.

   Of course, you don't have to delete the oldest generation of the data set, but there are

few data sets for which you need to keep all generations forever.
   Typical nomenclature for the generations of data sets is:

        Current version           Current generation
        Previous version          Parent or minus 1 version
        Next previous version     Grandparent or minus 2 version

   The data set naming convention uses a number to indicate the generation.

        DSN=data-set-name(0)     Current generation
        DSN=data-set-name(-1)    Previous generation or parent
        DSN=data-set-name(-2)    Next previous generation or grandparent

   The biggest advantage of using generation data groups is that the system keeps track of
the generations for you so you don't have to change your JCL each   time you run.
   Generation data groups consist of data sets that are normal except for their names.  The
data sets can be sequential, partitioned, or direct.  The benefit of using generation data
groups is that the system keeps track of the generations for you.  You don't have to keep
track of many individual data set names.

        For example:

        With normal data set names: With generation data group names:

        ACCT.DEC.DATA                   ACCT.DATA(0)
        ACCT.NOV.DATA                   ACCT.DATA(-1)
        ACCT.OCT.DATA                   ACCT.DATA(-2)

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