DFSMStvs Application Migration Guide

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Glossary

Access method control block (ACB). A control

block that links an application to a VSAM data set

Active control data set (ACDS). A VSAM linear

data set that controls the storage management

policy for an installation. It is shared by each

system that is using the same SMS configuration

to manage storage.

Active lock. A lock obtained by an executing

subsystem. Requests for locks incompatible with

a held active lock are queued. See also retained

lock.

Alternate index. A key-sequenced data set

containing index entries organized by the

alternate keys of its associated base data

records. It provides an alternative way of locating

records in the data set on which the alternate

index is based.

Application owning region (AOR). A CICS

region that does not own terminals or files but

which purely runs CICS transactions, relying

upon terminal-owning and file-owning regions for

terminal and file access.

Automatic class selection (ACS). A facility that

allows a DFSMS system to decide which

constructs (data class, storage class,

management class or storage group) should be

associated with a data set based on definition

attributes.

Automatic restart manager (ARM). An OS/390

component that provides recovery and restart

capabilities.

Back-out. Undo all changes made to a protected

resource since the previous sync point.

Basic sequential access method (BSAM). An

access method for sequentially organized

non-VSAM data that relies on an application

program to block and unblock data records.

CEMT. A CICS-supplied transaction used to

invoke all the master terminal functions. These

functions include inquiring and changing the

value of parameters used by CICS, altering the

status of system resources, terminating tasks and

shutting down CICS.

Cluster. A named VSAM structure consisting of a

group of one or more related components.

Consistent read (CR). A read operation where a

share lock is obtained and released as part of the

read process. This ensures that the reader sees

the latest committed copy of the record as at the

time of the read.

Consistent read explicit (CRE). A share lock is

obtained as part of the read process and held

until explicitly released. This ensures that a

subsequent read while the lock is still held will

always return the same version of the data.

Control area (CA). A fixed-size area in which

VSAM stores control intervals. It is the unit of

allocation for VSAM data.

Control interval (CI). A fixed-length area in

which VSAM stores records. It is the unit of

transfer between VSAM and disk storage.

Coupling Facility (CF). The hardware that

provides services to support data shared

between OS/390 systems.

Coupling Facility control code (CFCC). The

software running in a Coupling Facility that

provides Coupling Facility services.

Cross-system coupling facility (XCF). An MVS

component that provides services for the

exchange of messages between members of a

sysplex.

DFHLSCU. A CICS-supplied utility to calculate

space needed and average buffer size for log

streams.

DFR. An ACB parameter affecting buffer writing

when a data set is opened for LSR or GSR. It

defers the writing of a buffer until explicitly