Appendix A. Glossary

active IMS

(1) In an RSR environment, an IMS that runs at an active site, performs production work, and is monitored by the tracking IMS. Contrast with tracking IMS. (2) In an XRF environment, an IMS that performs production work and is monitored by the alternate IMS. Contrast with alternate IMS. (3) If FDBR is used, the IMS that performs production work. The active IMS is monitored by a separate Fast Database Recovery IMS control region.

AIB mask

A mapping that the application program uses to interpret the AIB.

alternate IMS

In an XRF environment, the IMS that monitors the active IMS and takes over production work when the active IMS fails. Contrast with active IMS.

application interface block (AIB)

application control block (ACB)

A control block that is created by the ACBGEN utility from the output of DBDGEN and PSBGEN utilities and placed in the ACB library for use during online and DBB region type execution of IMS.

area

A subset of a DEDB that is defined as a VSAM ESDS data set. Each area in a DEDB consists of a root-addressable part, an independent-overflow part, and a sequential-dependent part.

back-end system

An IMS in an MSC network that accepts transactions from the front-end system, calls application programs for transaction processing, and routes replies back to the front-end system for response to the terminal. Contrast with front-end system.

basic checkpoint

A point in an application program where the work of the application is committed. Unlike with a symbolic checkpoint, you cannot restart application from a basic checkpoint.

checkpoint

See synchronization point (sync point).

command code

The part of an SSA that tailors the call function, segment qualification, or setting of parentage to alter the results of a DL/I call.

control region

The z/OS main storage region that contains the IMS control program.

database description (DBD)

The collection of macro parameter statements that define the characteristics of a database, such as the database’s organization and access method, the segments and fields in a database record, and the relationship between types of segments.

database record

In a database, a collection of segments that contains one occurrence of the root segment type and all of its dependents arranged in a hierarchical sequence. It may be smaller than, equal to, or larger than the access method logical record.

database resource adapter (DRA)

An interface to IMS DB full-function databases and DEDBs. The DRA can be used by a coordinator controller (CCTL) or a z/OS application program that uses the ODBA interface.

data sharing

The concurrent access of databases by two or more IMSs. The IMSs can be in one operating system image or in separate operating system images. They can share data at two levels: the database level and the block level.

dependent region

An address space in which IMS application programs run. Dependent regions are managed by the IMS control region. Dependent region types are MPR, BMP, IFP, JMP, and JBP.

dependent segment

In a database, a segment that relies on a higher level segment for its full hierarchical meaning. A child is a dependent segment of its parent. Contrast with root segment.

DL/I

The IMS data manipulation language, which is a common high-level interface between an application program and IMS.

dynamic terminal

A terminal that is created through the Extended Terminal Option (ETO). A dynamic terminal is not defined within the IMS system definition, and no control blocks for the terminal exist at IMS initialization time. Contrast with static terminal.

expedited message handler (EMH)

The IMS Fast Path facility that processes single-segment input and output messages. Fast Path messages that use the EMH bypass the normal message queuing and application scheduling and therefore these messages are processed faster than non-Fast Path messages.

extended restart

A restart, initiated by a DL/I call, that reestablishes database positioning and user-specified areas.

field

In an IMS database, a portion (as defined in the DBD) within a segment that is the smallest unit of the data that can be referred to. See also sequence field.

field-level sensitivity

A restriction on an application program that allows access to only specific fields instead of all of the fields in a segment.

free space element (FSE)

In a hierarchical direct database, the first 8 bytes of an area that is free space. The FSE describes the area of free space in a CI or block that is 8 or more bytes in length.

free space element anchor point (FSEAP)

In a hierarchical direct database, the first 4 bytes of a CI or block. The first 2byte field contains the offset, in bytes, to the first FSE in the CI or block. The second 2byte field identifies whether this block or CI contains a bit map.

front-end system

An IMS in an MSC network in which all terminals are connected, messages are routed to the proper back-end IMS, and all replies are routed to the terminals. Contrast with back-end system.

fuzzy image copy

An image copy of an online database. The database can be updated while the image copy is being taken and some, all, or none of the updates might appear in the image copy. Also called concurrent image copy.

image copy

(1) The process of creating a backup of a DBDS. (2) The backup data set created by the image copy process. See also fuzzy image copy.

IMSplex

One or more IMSs that work together as a unit. Typically these IMSs share resources, run in a Parallel Sysplex environment, and include a CSL.

indirect list data set (ILDS)

In a HALDB, an IMS system index data set. The ILDS is a repository for the indirect pointers used for PHDAM and PHIDAM databases. There is one ILDS per partition in PHDAM or PHIDAM databases.

indirect list entry (ILE)

In a HALDB, an entry in an indirect list data set.

indirect list entry key (ILK)

In a HALDB, a unique token that is assigned to a segment in PHDAM and PHIDAM databases when the segment is created. Eight bytes in length and stored in the prefix of the segment, the ILK uniquely identifies every segment in PHDAM and PHIDAM databases.

indirect pointer

In a HALDB, a pointer that is stored in the indirect list data set and that is used to eliminate the need to update pointers throughout other database records when a single partition is reorganized. Indirect pointers are stored in an indirect list data set.

logical database

A set of logical database record occurrences. It is composed of one or more physical databases; it represents hierarchical, structured relationships between data segments that can be different from the physical structure in which the segments were loaded. Contrast with physical database.

logical relationship

In a database, a user-defined path between two independent segments.

logical unit

An addressable resource such as an application program, a terminal, or a subsystem. For IMS, a logical unit is usually a terminal that logs onto IMS to do work.

master terminal

The IMS logical terminal that has complete control of IMS resources during online operations.

message

Data that is transmitted between any two terminals, application programs, or IMS systems. Each message has one or more segments.

message class

A class, assigned to a transaction code, that determines within which message region an application program is to process that transaction. See also region class and transaction code.

message queue

The data structure in which messages are queued before being processed by an application program or sent to a terminal. Local message queues are in IMS control regions and shared message queues are in coupling facility structures. See also shared queues.

online change

An IMS function that supports the adding, changing, or deleting of IMS resources such as transactions, database directories, program directories, DMBs, PSBs, and Fast Path routing codes without stopping the system to define them.

online log data set (OLDS)

A data set on direct access storage that contains the log records written by an online IMS system.

online reorganization

Database reorganization, which is available only for HALDBs and DEDBs, during which the database remains available for updates during the reorganization process.

partition

A subset of a HALDB that has the capacity of a non-HALDB database and that can be administered independently.

path call

A type of DL/I call that enables a hierarchical path of segments to be inserted or retrieved with one call.

PCB mask

A mapping in the application program that the application uses to interpret a PCB.

physical database

An ordered set of physical database records. Contrast with logical database.

program communication block (PCB)

(1) A component of a PSB that describes the application’s view of a database or a message destination. (2) A control block that, during runtime, has status information from IMS about the application’s current DL/I call. The application interprets the PCB through its PCB mask.

program isolation

An IMS facility that separates all the activity of an application program from any other active application program until that application program indicates, using a synchronization point, that the data it has modified or created is consistent and complete.

program specification block (PSB)

The control block that describes the databases and logical message destinations that are used by an application program. A PSB consists of one or more PCBs. See also program communication block (PCB).

overflow area

In an HDAM or PHDAM database, the area in which IMS stores data when the root addressable area does not have enough space for a segment. Contrast with root addressable area.

qualified SSA

An SSA that contains, in addition to the segment name, one or more qualification statements. A qualified SSA describes the segment type and occurrence that is to be accessed.

RECON data set

A data set in which DBRC stores information about logging activity and events that might affect the recovery of databases.

region class

The class that IMS assigns to a message region that indicates the message classes that can be processed within the region. See also message class.

root addressable area

In an HDAM or PHDAM database, the primary storage area in HDAM and PHDAM databases. IMS always attempts to put new and updated segments in the root addressable area, and if there is not enough room, IMS puts the segment into the overflow area instead. Contrast with overflow area.

root anchor point (RAP)

In an HDAM database or DEDB, a pointer at the beginning of each block or CI that points to a root segment that belongs in that block and that chains the root segments that randomize to that CI or block.

root segment

The highest segment in the database hierarchy. The database is normally sequenced on the key field of this segment. All other segments depend upon the root segment and reference it as part of their complete identity. Contrast with dependent segment.

scratch pad area (SPA)

A work area that is used in conversational message processing to retain information from an application program across executions of the program.

secondary index

An index that is used to establish accessibility to a physical or logical database by a path different from the one provided by the database definition. It contains an index pointer segment type that is defined in a secondary index database.

segment

The unit of access for IMS. For IMS DB, a segment is the smallest amount of data that can be transferred by one IMS operation. For input terminal operations using IMS TM, a segment is defined by the particular terminal type and is obtained by an application program with one call.

segment search argument (SSA)

The portion of a DL/I call that identifies a segment or group of segments to be processed. Each SSA contains a segment name and, optionally, one or more command codes, and one or more qualification statements. Multiple SSAs may be required to identify the desired segment. See also qualified SSA and unqualified SSA.

sequence field

The field in a database segment that used to store segment occurrences in sequential ascending order. Also called a key field.

shared queue

A collection of data objects with the same name that reside on a coupling facility queue structure. Data objects on a shared queue are available to all CQS clients that have access to the structure. See also message queue.

sibling segments

Two or more occurrences of different segment types having a common parent segment occurrence. Contrast with twin segments.

single point of control (SPOC)

The control interface that sends commands to one or more members of an IMSplex and receives command responses.

static terminal

A terminal that is created through the IMS system definition process. Contrast with dynamic terminal.

symbolic checkpoint

A checkpoint in a batch, BMP, or JBP application that indicates to IMS that the program has reached a commit point and that establishes a place in the program from which the application can be restarted. See also extended restart.

synchronization point (sync point)

A point in time from which IMS or an application program can start over if a failure makes recovery necessary. The two types of synchronization points are system checkpoints, which are done by IMS itself, and application program checkpoints, which are done on behalf of individual application programs.

system definition

An IMS process that describes databases, application programs, terminals, and other resources to IMS.

system log data set (SLDS)

The permanent destination data set for IMS log records. The SLDS is usually on tape or MSS. In an IMS batch region, the SLDS is created at execution time. In an IMS online region, the SLDS is created by the Log Archive utility from the OLDS. Contrast with online log data set (OLDS) and write-ahead data set (WADS).

tracking IMS

In an RSR environment, an IMS that tracks the activities of active IMSs to provide disaster recovery support. A tracking IMS is usually geographically remote from the active IMSs. contrast with active IMS.

transaction

(1) A single conversation iteration, from entering of an input message to receipt of one or more output messages in response. (2) A common way of referring to a transaction code.

transaction code

A 1- to 8-character alphanumeric code that invokes an IMS message processing program.

twin segments

In a database, all child segments of the same segment type that have a particular instance of the same parent segment type. Root segments are also considered twins to each other. Contrast with sibling segments.

type-1 command

A command, generally preceded by a leading slash character, that can be entered from any valid IMS command source. Contrast with type-2 command.

type-2 command

A command that is entered only through the OM API. Type-2 commands are more flexible and can have a broader scope than type-1 commands. Contrast with type-1 command.

unqualified SSA

An SSA that contains only one segment name. Contrast with qualified SSA.

write-ahead data set (WADS)

A data set that contains log records that reflect completed operations and are not yet written to an OLDS. Contrast with online log data set and system log data set.