data set organization
<operating system, storage> (DSORG) An IBM term for file structure. These
include PS physical sequential, DA direct, IS indexed sequential, PO partitioned
(a library). This system dates from OS/360, and breaks down beginning with VSAM
and VTAM, where it is no longer applied.
Sequential and indexed data sets can be accessed using either a "basic" or a
"queued" "access method." For example a DSORG=PS file can use either BSAM (basic
sequential access method) or QSAM (queued sequential access method). It can also
be processed as a direct file using BDAM. Likewise a library can be processed
using BPAM (basic partitioned access method), BSAM, QSAM, or BDAM. DSORG and
access method are somewhat, but not completely, orthogonal.
The "basic" access method deals with physical blocks rather than records, and
usually provides more control over the specific device. Each I/O operation using
the "basic" access method reads or writes a single block. A "basic" read or
write starts an asynchronous I/O operation, and the programmer is responsible
for waiting for completion and checking for errors.
The "queued" access method deals with logical records and provides blocking and
deblocking services. It is "queued" because it provides read-ahead and
write-behind services. While a program is processing records in one input block,
for example, QSAM may be reading one or more blocks ahead. Queued "get" or "put"
operations are synchronous as far as the programmer is concerned. The operation
is complete when the next logical record has been successfully processed.
EXCP (Execute Channel Program) is a lower-level method of accessing data.
IBM manuals usually named "Data Administration Guide", e.g. SC26-4505-1 for
MVS/ESA DFP 3.1, provide more detail about data set organizations and access
data segment « data service unit « data set «
data set organization » DataStage » Datastorm
Technologies, Inc. » data striping