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algorithm
A finite set of well-defined rules for the solution of a problem in a finite number of steps, for example, a specific set of steps used to compress or expand a record.
analysis file
The data set used by the CA Compress Interactive User Interface to record the results of compression analysis and implementation performed by the IUI.
BDA
Byte Distribution Analysis. The process of analyzing the distribution of characters in a data set in order to construct the Huffman tables used to compress and expand the data set.
buffer
Storage allocated to temporarily hold input or output data.
CA Compress started task
Running in its own address space, the started task supports the SVC intercepts, cross-memory services, and other facilities required to support compression transparently for application programs.
CA Compress/2 subroutines
Compression and expansion subroutines, used by CA Compress, which can also be called by users. These subroutines are especially useful for supporting compression in products with data that CA Compress cannot support transparently.
CA Compress/2 utilities
Utilities that can be used to perform compression and expansion when the CA Compress subsystem is unavailable.
CFMU
Control File Maintenance Utility. A batch utility provided with CA Compress for maintaining the Control File.
checkbyte
An extra byte calculated and added to the compressed data. If it does not exactly match the expected result at expansion, the compressed data has been damaged, perhaps through overlay or truncation when written.
compression algorithm
A finite set of rules used to collect and assign values to the characters found in a string of data so that the data takes less space.
compression overhead
The processing required to compress data as it is transferred from the application to the data set.
control file
The data set used by CA Compress to record the data sets controlled by CA Compress and how CA Compress should handle them.
discrete data set
A single data set, as opposed to a pattern defining a number of data sets.
dynamic allocation
1. Assignment of system resources to a program at the time the program is executed rather than at the time it is loaded into main storage.
2. The IBM facility provided through SVC 99 to accomplish this purpose.
exclusion feature
A facility enabling the user to supply tables of jobs and programs for which compression and expansion should not take place in order to prevent unnecessary compression and expansion or double compression.
expansion overhead
The processing required to expand data as it is transferred from the data set to the application.
express
The CA Compress string compression algorithm that was replaced by the Super Express algorithm.
FDT
File Descriptor Table. A load module that also exists as records on the Analysis and Control Files. It contains information required to compress and expand the data set, including its Huffman compression and expansion tables.
FDTLIB
The load library in which the Interactive User Interface stores FDTs, and from which it and the CFMU copy FDTs to the Control File.
file analysis
The process by which CA Compress presents the various compression choices and the compression percentages possible.
huffman
A compression algorithm that uses tables to replace each character by a variable-length bit string. The characters expected to occur most often are assigned the shortest bit lengths.
ICB
Integrity Check Block. A 3-byte field preceding the compressed data by which CA Compress recognizes the algorithm used to compress the data.
implementation
Placing a data set under CA Compress control.
interactive user interface (IUI)
The ISPF interface of CA Compress.
linklist
The list of load module libraries chosen by the installation to be searched by default after any STEPLIB or JOBLIB libraries.
LSR
Local Shared Resources. The IBM facility for permitting buffers to be shared by VSAM data sets in a job step. Because I/O to DASD is greatly reduced for random processing in most cases, performance is much improved even for a single data set.
PASSTHRU
A facility to enable CA Compress processing without actually performing compression or expansion.
pattern
A name with variable characters used to implement a particular compression algorithm for all data sets matching the pattern.
pattern analysis
The process by which CA Compress will search for data sets to analyze based on name.
pattern matching
The process of implementing a data set when it matches a pattern in the Control File, rather than explicitly by name.
RDL
Record Definition Language. The language supplied with CA Compress to define compression on each record. RDL is usually generated by default, but can be modified by the user.
RDW
Record Descriptor Word. The first 4 bytes of a variable length non-VSAM record or segment, which defines its length.
safeguards
A CA Compress facility for preventing inadvertent access to compressed VSAM data sets when the CA Compress subsystem is not active.
SAM-SI
Sequential Access Method-Subsystem Interface. The IBM access method used to support the SUBSYS JCL keyword. It is also invoked by Physical Sequential Transparency. Its limitations require certain special considerations when implementing compression using the SUBSYS JCL parameter.
scheduled
A method of implementing compression at a specified future event either when the VSAM data set is next loaded or when it is opened for output.
SDB
System Determined Blocksize, in which the user codes BLKSIZE=0 to cause the system to select an optimal block size for the device.
SHRVL
A CA Compress compression algorithm that achieves high compression for relatively high CPU overhead on certain types of data.
space release
The facility for freeing unused space from compressed VSAM data sets.
standard tables
Six compression tables distributed with CA Compress.
SUBSYS
An IBM JCL DD parameter for non-VSAM data sets that invokes a subsystem to process the ddname on which it is coded.
subsystem
A facility running under MVS that performs a certain function. JES2 and JES3, for example, handle job entry and throughput, and SMS does storage management.
super express
The CA Compress string compression algorithm. It compresses repetitive characters without using tables.
TCF
Test Compression Facility.
VPE
VSAM Performance Enhancement.
VPE rules
Rules supplied to VPE to direct its optimization of data sets.
VPE rules table
The table of rules built by VPE in extended CSA and addressed through the entry for VPE in the subsystem control table (SSCT). VPE does not run as a true subsystem or started task, but in this way VPE can recognize rules built before it is activated.
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