The DSN parameter refers to the physical dataset name of a newly created or existing dataset. The DSN value can be made up of sub-names each of 1 to 8 characters length, separated by periods and of total length of 44 characters alphanumeric. This is called Backward Referencing. Concatenating Datasets If there is more than one dataset of the same format, they can be concatenated and passed as an input to the program in a single DD name. Overriding Datasets In a standardised JCL, the program to be executed and its related datasets are placed within a cataloged procedure, which is called in the JCL.
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LIFO concatenation orders the most recent generation data set first, followed by the next most recent data set, continuing to the oldest generation data set, which is last. FIFO first in, first out concatenation orders the oldest data set first, continuing to the most recent data set, which is last.
Any error message uses the relative position based on each generation included, not the position you explicitly specified. All older generations have unit affinity to the newest data set. If you code MOD for a generation data set and the specified relative generation does not exist in the catalog, the system changes the status to NEW. A normal termination disposition is optional when retrieving a generation data set but is required in a GDG ALL request.
Or, if the data set resides on more than one volume and you want as many devices as there are volumes, code P in the UNIT parameter. For an old generation data set, do not specify either a volume serial number or a volume reference to another data set or to an earlier DD statement.
If the data set is not the first data set on the volume, specify the data set sequence number. If the data set sequence number is coded for a GDG ALL request, it is ignored; the data set sequence number is obtained from the catalog.
Retrieving all generation data sets
Keyword, optional Purpose Use the DISP parameter to describe the status of a data set to the system and tell the system what to do with the data set after termination of the step or job. You can specify one disposition for normal termination and another for abnormal termination. Note that if an abend occurs within a step, the step itself may terminate normally or abnormally, depending on whether an ESTAE or ESPIE routine intercepts the abend and requests that processing continue. Normal termination of a step is indicated by the presence of message IEFI; abnormal termination of a step is indicated by the presence of message IEFI. Note: Disposition of the data set is controlled solely by the DISP parameter; disposition of the volume s on which the data set resides is a function of the volume status when the volume is demounted.
JCL - Defining Datasets
GDG in JCL