Creating a Sequential Data Set

Use either the QSAM or the BSAM to store and retrieve the records of a sequential data set. To create a sequential data set on magnetic tape or DASD, take the following actions:

Code DSORG=PS or PSU in the DCB macro.
Do one of the following:
- Code a DD statement to describe the data set. See z/OS MVS JCL Reference. If SMS is implemented on your system, you can specify a data class in the DD statement or have the ACS routines assign a data class.
- Create the data set using the TSO or access method services ALLOCATE command. See z/OS DFSMS Access Method Services Commands. If SMS is implemented on your system, you can specify the DATACLAS parameter or have the ACS routine assign a data class.
- Call dynamic allocation (SVC 99) from your program. See z/OS MVS Programming: Authorized Assembler Services Guide. If SMS is implemented on your system, you can specify the data class text unit or have the ACS routines assign a data class.
Optionally, use a data class to simplify and standardize data attributes. You can take advantage of a data class for data sets that are system managed or not system managed.
Process the data set with an OPEN macro (the data set is opened for OUTPUT, OUTIN, OUTINX, or EXTEND), a series of PUT or WRITE and CHECK macros, and the CLOSE macro.

The example in Figure 1 shows that the GET-move and PUT-move require two movements of the data records.

Figure 1. Creating a Sequential Data Set—Move Mode, Simple Buffering

         OPEN   (INDATA,,OUTDATA,(OUTPUT))
NEXTREC  GET    INDATA,WORKAREA              Move mode
         AP     NUMBER,=P'1'
         UNPK   COUNT,NUMBER                 Record count adds 6
         OI     COUNT+5,X'F0'                Set zone bits
         PUT    OUTDATA,COUNT                bytes to each record
         B      NEXTREC
ENDJOB   CLOSE  (INDATA,,OUTDATA)
         ...
COUNT    DS     CL6
WORKAREA DS     CL50
NUMBER   DC     PL4'0'
SAVE14   DS     F
INDATA   DCB    DDNAME=INPUTDD,DSORG=PS,MACRF=(GM),EODAD=ENDJOB,       X
               LRECL=50,RECFM=FB
OUTDATA  DCB    DDNAME=OUTPUTDD,DSORG=PS,MACRF=(PM),                   X
               LRECL=56,RECFM=FB
         ...

If the record length (LRECL) does not change during processing, but only one move is necessary, you can process the record in the input buffer segment. A GET-locate provides a pointer to the current segment.

Related reading: See QSAM in an Application for more information.