In this example, a generation data group is defined in the master catalog. Next, a generation data set is defined within the GDG by using JCL statements.

//DEFGDG1  JOB    ...
//STEP1    EXEC   PGM=IDCAMS
//GDGMOD   DD     DSNAME=GDG01,DISP=(,KEEP),
//         SPACE=(TRK,(0)),UNIT=DISK,VOL=SER=VSER03,
//         DCB=(RECFM=FB,BLKSIZE=2000,LRECL=100)
//SYSPRINT DD     SYSOUT=A
//SYSIN    DD     *
    DEFINE GENERATIONDATAGROUP -
           (NAME(GDG01) -
           EMPTY -
           NOSCRATCH -
           LIMIT(255) )
/*
//DEFGDG2  JOB    ...
//STEP1    EXEC   PGM=IEFBR14
//GDGDD1   DD     DSNAME=GDG01(+1),DISP=(NEW,CATLG),
//         SPACE=(TRK,(10,5)),VOL=SER=VSER03,
//         UNIT=DISK
//SYSPRINT DD     SYSOUT=A
//SYSIN    DD     *
/*

Job control language statement:

• GDGMOD DD, which describes the GDG. When the scheduler processes the DD statement, no space is allocated to GDG01.

The DEFINE GENERATIONDATAGROUP command defines a GDG base catalog entry, GDG01. Its parameters are:

• NAME specifies the name of the GDG, GDG01. Each GDS in the group will have the name GDG01.GxxxxVyy, where xxxx is the generation number and yy is the version number.
• EMPTY specifies that all data sets in the group are to be uncataloged by VSAM when the group reaches the maximum number of data sets (as specified by the LIMIT parameter) and one more GDS is added to the group.
• NOSCRATCH specifies that when a data set is uncataloged, its DSCB is not to be removed from its volume's VTOC. Therefore, even if a data set is uncataloged, its records can be accessed when it is allocated to a job step with the appropriate JCL DD statement.
• LIMIT specifies that the maximum number of GDGs in the group is 255. The LIMIT parameter is required.