| slovo | definícia |
data set
(foldoc) | data set
An IBM term for a file.
(1997-04-15)
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| | podobné slovo | definícia |
data set organization
(foldoc) | data set organization
DSORG
(DSORG) An IBM term for file
structure. These include PS physical sequential, DA {direct
access}, 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 methods.
(2005-08-08)
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entry sequenced data set
(foldoc) | Entry Sequenced Data Set
(ESDS) An IBM straight sequential flat file (like
QSAM) but externally managed via IDCAMS. ESDS is used in
VSAM.
(1999-01-11)
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keyed sequenced data set
(foldoc) | Keyed Sequenced Data Set
(KSDS) One of the access methods used by VSAM.
KSDS has indexes and data split into CI (Control Interval) in
CA (Control Area) and multi index levelled. Forward and
backward compression is applied to key values.
(1999-01-11)
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partitioned data set
(foldoc) | partitioned data set
(PDS) A data set on an IBM mainframe that
contains members, each of which acts like a separate data set.
Partitioned data sets are more space-efficient than individual
data sets, because they can put more than one data set on a
track. They are also used to hold libraries, with one
function per member. The syntax for a member is
NAME.OF.PDS(MEMBER) although some systems (such as Phoenix)
could use NAME.OF.PDS:MEMBER
Original PDSes were of fixed size, and needed frequent
compression to recover space after deleting or changing
members. Newer PDS/E Extended PDSes do not have this problem.
(2003-12-05)
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relative record data set
(foldoc) | Relative Record Data Set
(RRDS) One of the access methods used by IBM's
VSAM.
[What is it?]
(1999-01-12)
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