The processing of input files without labels is requested by means of the operand LABEL=NO of the FILE macro or the operand LABEL-TYPE=*NO of the ADD-FILE-LINK command.
Regardless of the user entry for LABEL or LABEL-TYPE, the volume header label is always checked unless the VOL1 check has already been performed for this tape.
Checking labels
DMS first checks whether the tape starts with a VOL1 label. If not, the job can access the file with no further checks (see section "Files without labels" below). If, in spite of the specification LABEL=NO or LABEL-TYPE=*NO, the tape starts with a VOL1 label, the validity of the VSN is first checked. As for files with standard labels, DMS issues either message DMS0DA1 or, for foreign files, message DMS0DFB to the operator.
Next, DMS uses the VOL1 access indicator and owner identifier to check whether the user ID may access the tape (error message: DMS0DD7). DMS then reads the HDR labels and checks the access authorization on the basis of the HDR1 access indicator and the HDR3 owner identifier (error message: DMS0DD7). If the file is to be opened with OPEN INOUT/EXTEND, the HDR3 access type and the HDR1 expiration date are checked (error message: DMS0DA3). In interactive mode, DMS issues error message DMS0DF6 to inform the user that the LABEL specification does not match the tape contents. The user can then decide whether he/she still wants to process the file, i.e. that the program is to be continued, or that the program is to be terminated with an OPEN error.
Positioning
If the first record on the tape is not a VOL1 label, but a tape mark, and if TPMARK=YES (see the FILE/FCB macro) or TAPE-MARK-WRITE=*YES (see the ADD-FILE-LINK command) was specified, DMS positions the tape after this tape mark. Within the tape, DMS executes positioning as specified in the FSEQ field of the catalog entry or the FILE or FCB macro, or as specified in the FILE-SEQUENCE operand of the ADD-FILE-LINK command.