MVS provides a direct connection between the filename used in the program and the corresponding data set name used in the JCL. For example, for SYSUT1 in a COBOL program:
SELECT INFILE ASSIGN TO UT-S-SYSUT1
connects to
//SYSUT1 DD DSN=DSNAME1,DISP=OLD
and allocates to the program the PC file representing the data set named DSNAME1.
And, for SYSUT2:
SELECT OUTFILE ASSIGN TO UT-S-SYSUT2
connects to
//SYSUT2 DD DSN=DSNAME2,DISP=(NEW,CATLG),...
and allocates to the program a PC file representing the data set named DSNAME2. The file is created and cataloged automatically when the jobstream is run.