Use of postponing specification

Use the DDNAME parameter in cataloged procedures to postpone defining an in-stream data set until a job step calls the procedure. JES3 procedures cannot contain DD statements that define in-stream data sets and cannot contain in-stream data.

Use the DDNAME parameter in a job step that calls a procedure to postpone defining in-stream data until the last overriding DD statement for a procedure step. Overriding DD statements must appear in the same order as the DD statements in the procedure and any in-stream data sets must appear last in a calling step.

Example 1

//XYZ   DD  DDNAME=PHOB
        .
        .
        .
//PHOB  DD  DSNAME=NIN,DISP=(NEW,KEEP),UNIT=3400-5

From DD statement XYZ, the system saves XYZ and, temporarily, PHOB. Until the system encounters the ddname PHOB, it treats the data set for XYZ as a dummy data set.

When the system reads DD statement PHOB, it uses the DSNAME, DISP, and UNIT values to define the data set named NIN. The system also associates this information with DD statement XYZ. The system stops saving ddname PHOB. The data set is now defined as if you had coded:

//XYZ  DD  DSNAME=NIN,DISP=(NEW,KEEP),UNIT=3400-5

Example 2

//DD1  DD  DDNAME=LATER
   .
   .
   .
//LATER  DD  DSN=SET12,DISP=(NEW,KEEP),UNIT=3390,
//           VOLUME=SER=46231,SPACE=(TRK,(20,5))
   .
   .
   .
//DD12  DD  DSN=SET13,DISP=(NEW,KEEP),VOLUME=REF=*.DD1,
//          SPACE=(TRK,(40,5))

DD1 postpones defining the data set until the system encounters DD statement LATER. DD12 must do a backward reference to DD1 because the system associates the data set information with the DD statement that contains the DDNAME parameter.

Example 3

//DDA  DD  DDNAME=DEF
//     DD  DSN=A.B.C,DISP=OLD
//     DD  DSN=SEVC,DISP=OLD,UNIT=3390,VOL=SER=52226
   .
   .
   .
//DEF  DD  *
   data
/*

This example shows correct concatenation when a DDNAME parameter is coded.