DFSMSdfp access

DFSMSdfp™ provides several access methods for formatting and accessing data. An access method defines the organization of the data in a data set and the technique by which the data is stored and retrieved. DFSMSdfp access methods have their own data set structures to organize data, macro instructions to process data sets, and utility programs to manipulate data sets.

Table 1 describes the access methods that DFSMSdfp uses.

Table 1. DFSMSdfp access methods
Access method	Description	Data set organization
Basic partitioned access method (BPAM)	Use BPAM to create and retrieve program and data libraries on DASD. BPAM arranges records as members of PDSs, PDSEs, or z/OS® UNIX® directories.	PDS PDSE z/OS UNIX
Basic sequential access method (BSAM)	Use BSAM to process data sets sequentially. You organize the records into blocks for retrieval.	Sequential data sets Extended-format data sets PDS members PDSE members z/OS UNIX files
Object access method (OAM)—OSREQ interface	Use OAM to store, back up, and retrieve objects on DASD, optical, and tape storage.	Objects
Queued sequential access method (QSAM)	Use QSAM to process data sets sequentially. QSAM collects the records into blocks.	Sequential data sets Extended-format data sets PDS members PDSE members z/OS UNIX files
Virtual storage access method (VSAM)	Use VSAM for direct or sequential processing of records on DASD. VSAM arranges records by an index key, by relative byte address, or by relative record number. VSAM catalogs data sets for easy retrieval.	Entry-sequenced data sets Key-sequenced data sets Linear data sets Relative record data sets HFS files

DFSMS™ also supports the basic direct access method (BDAM) for coexistence with previous operating systems.

You can use assembler language macro instructions to create, maintain, and process all the data set types supported by the access methods described in Table 1. Macro instructions control data set allocation, input and output, and data security.

Each compiler provides facilities to create, read, and write data sets. Your compiler documentation describes how to use the access method facilities.

The following are a few of the functions that the macro instructions perform:

Control block macros generate information that the access method needs to process the data sets.
Request macros retrieve, update, delete, or insert logical records into data sets.
Checkpoint/restart functions establish checkpoints during a program and restart the job at a checkpoint or at the beginning of a job step.