DB2 UDB terms

A

abnormal termination
(1) The cessation of processing prior to planned termination. (T)
(2) A system failure or operator action that causes a job to end unsuccessfully.
(3) In DB2, exits that are not under program control, such as a trap or segv.

access path
The method that is selected by the optimizer for retrieving data from a specific table. For example, an access path can involve the use of an index, a sequential scan, or a combination of the two.

access plan
The set of access paths that are selected by the optimizer to evaluate a particular SQL statement. The access plan specifies the order of operations to resolve the execution plan, the implementation methods (such as JOIN), and the access path for each table referenced in the statement.

accounting string
User-defined accounting information that is sent to DRDA servers by DB2 Connect. This information can be specified at one of these locations:

active log
The subset of files consisting of primary and secondary log files that are currently needed by the database manager for crash recovery and rollback. Contrast with archive log.

adjacent nodes
Two nodes connected together by at least one path that connects no other nodes. (T)

administrative authority
A level of authority that gives a user privileges over a set of objects. For example, DBADM authority gives privileges over all objects in a database, and SYSADM authority gives privileges over all objects in a system.

ADSM
ADSTAR Distributed Storage Manager.

ADSTAR Distributed Storage Manager (ADSM)
A client/server product that provides storage management and data access services in a heterogeneous environment. It supports various communication methods, provides administrative facilities to manage the backup and storage of files, and provides facilities for scheduling backup operations.

Advanced Peer-to-Peer Networking (APPN)
An extension to SNA that features greater distributed network control, dynamic definition of network resources, and automated resource registration and directory lookup.

Advanced Peer-to-Peer Networking (APPN) network
A collection of interconnected network nodes and their client end nodes. See also network node.

Advanced program-to-program communication (APPC)
The general facility that characterizes the LU 6.2 architecture and its various implementations in products.

after-image
The updated content of a source table element that is recorded in a change data table or in a database log or journal. Contrast with before-image.

agent
A separate process or thread that carries out all DB2 requests that are made by a particular client application.

aggregate function
Synonym for column function.

alert
An action, such as a beep or warning, that is generated when a performance variable exceeds or falls below its warning or alarm threshold.

alias
In DB2, an alternative name used to identify a table, view, database or nickname.

alias chain
A series of table aliases that refer to each other in a sequential, non-repeating fashion.

alphanumeric
Pertaining to data that consists of letters, digits, and usually other characters, such as punctuation marks. (T) (A)

ambiguous cursor
A cursor that cannot be determined to be updateable or read-only from its definition or context.

API
Application programming interface.

APPC
Advanced program-to-program communication.

application ID
A string that uniquely identifies an application across networks. An ID is generated at the time that the application connects to the database. This ID is known on both the client and the server and can be used to correlate the two parts of the application.

application process
The unit to which resources and locks are allocated. An application process involves the running of one or more programs.

application programming interface (API)
(1) A functional interface supplied by the operating system or by a separately orderable licensed program. It allows an application program written in a high-level language to use specific data or functions of the operating system or the licensed programs.
(2) In DB2, a function within the interface. For example, the get error message API.

application requester
A facility that accepts a database request from an application process and passes it to an application server.

application server
The local or remote database manager to which the application process is connected.

Apply program
A replication program that is used to refresh or update a target table, depending on the applicable source-to-target rules. Contrast with Capture program.

Apply qualifier
A character string that identifies subscription definitions that are unique to each instance of the Apply program.

Apply trail table
A replication source table at the control server that records a history of the refreshes and updates performed against target tables.

APPN
Advanced Peer-to-Peer Networking.

APPN network node
Advanced Peer-to-Peer Networking (APPN) network node. Synonymous with network node.

archive log
The set of log files that are closed and are no longer needed for normal processing. These files are retained for use in roll-forward recovery. Contrast with active log.

argument
A value passed to or returned from a function or procedure at run time.

asynchronous
Without regular time relationship; unexpected and unpredictable with respect to the processing of program instructions. Contrast with synchronous.

asynchronous batched update
A process in which all changes to the source are recorded and applied to existing target data at specified intervals. Contrast with asynchronous continuous update.

asynchronous continuous update
A process in which all changes to the source are recorded and applied to existing target data after being committed in the base table. Contrast with asynchronous batched update.

attach
In DB2, to remotely access objects at the instance level.

audit trail
Data, in the form of a logical path linking a sequence of events, used for tracing the transactions that have affected the contents of a record. (T)

authorization
In computer security, the right granted to a user to communicate with or make use of a computer system. (T)

authorization ID
A character string in a statement that designates a set of privileges. It is used by the database manager for authorization checking and as an implicit qualifier for the names of objects such as tables, views, and indexes.

autocommit
To automatically commit the current unit of work after each SQL statement.

automatic rebind
A feature that automatically rebinds an invalidated package without requiring a bind command to be entered manually or a bind file to be present.

auto-registration
A process in which replica and consistent change data tables are automatically defined as replication sources at the target server.



B

backup pending
The state of a database or table space that prevents an operation from being performed until a backup is made of the database or table space.

base aggregate table
A target table type that contains data aggregated from a source table or a point-in-time table at intervals.

base table
A table created with the CREATE TABLE statement. Such a table has both its description and data physically stored in the database. Contrast with view.

basic conversation
An LU 6.2 conversation type between two transaction programs using the APPC basic conversation API. Contrast with mapped conversation.

basic predicate
A predicate that compares two values.

before-image
The content of a source table element prior to a refresh or update, as recorded in a change data table, or in a database log or journal. Contrast with after-image.

binary large object (BLOB)
A sequence of bytes, where the size of the sequence ranges from 0 bytes to 2 gigabytes. This string does not have an associated code page and character set. Image, audio, and video objects are stored in BLOBs.

bind
In SQL, the process by which the output from the SQL precompiler is converted to a usable structure called an access plan. During this process, access paths to the data are selected and some authorization checking is performed.

bindery object name
A 48-byte character string that contains the name of a bindery object on the NetWare** file server. The database manager configuration field, objectname, uniquely represents a DB2 server instance, and is stored as an object in the bindery on a NetWare file server.

bind file
A file produced by the precompiler when the bind command or API is used with the BINDFILE option. This file includes information on all SQL statements in the application program.

bit data
Data that is not associated with a coded character set and is therefore never converted.

BLOB
Binary large object.

block
A string of data elements recorded or transmitted as a unit.

blocking
An option that is specified when binding an application. It allows caching of multiple rows of information by the communications subsystem so that each FETCH statement does not require the transmission of one row for each request across the network.

broadcast join
A join in which all partitions of a table are sent to all nodes.

built-in function
An SQL function that is provided by DB2 and appears in the SYSIBM schema. Contrast with user-defined function.

byte reversal
A technique in which numeric data is stored with the least significant byte first.



C

cache
A buffer that contains frequently accessed instructions and data; it is used to reduce access time.

Call Level Interface (CLI)
A callable API for database access, which is an alternative to an embedded SQL API. In contrast to embedded SQL, CLI does not require precompiling or binding by the user, but instead provides a standard set of functions to process SQL statements and related services at run time.

Capture program
A replication program that reads database log or journal records to capture data about changes made to source tables. Contrast with Apply program.

cardinality
The number of rows in a database table.

cascade rejection
The process of rejecting a replication transaction because it is associated with a transaction that had a conflict detected and was itself rejected.

cast function
A function used to convert instances of a data type (origin) into instances of a different data type (target). In general, cast functions have the name of the target data type. They have one single argument whose type is the origin data type; their return type is the target data type.

catalog
A set of tables and views maintained by the database manager. These tables and views contain information such as descriptions of tables, views, and packages.

catalog node
The node at which the catalog tables reside. The catalog node can be a different node for each database.

CCSID
Coded character set identifier.

CDRA
Character Data Representation Architecture.

change aggregate table
A type of target table that contains data aggregations based on changes recorded for a source table.

change data (CD) table
A replication control table at the source server that contains changed data for a replication source table. The Capture program populates the CD table by copying the changes from the database log or journal. The contents of the CD table are then copied by the Apply program to the target table.

Character Data Representation Architecture (CDRA)
An architecture used to achieve consistent representation, processing, and interchange of string data.

character large object (CLOB)
A sequence of characters (single-byte, multi-byte, or both) where the length can be up to 2 gigabytes. A data type that can be used to store large text objects. Also called character large object string.

character string
A sequence of bytes or characters.

character string delimiter
The characters used to enclose character strings in delimited ASCII files that are imported or exported. See delimiter.

check condition
A restricted form of search condition used in check constraints.

check constraint
Specifies a check condition that is not false for each row of the table on which the constraint has been defined.

check pending
A state into which a table can be put where only limited activity is allowed on the table and constraints are not checked when the table is updated.

circular log
A database log in which records are overwritten if they are no longer needed by an active database. Consequently, if a failure occurs, lost data cannot be restored during forward recovery. Contrast with recoverable log.

CLI
Call Level Interface.

client
Any program (or workstation it is running on) that communicates with and accesses a database server.

CLOB
Character large object.

CLP
Command Line Processor.

clustered index
An index whose sequence of key values closely corresponds to the sequence of rows stored in a table. The degree to which this correspondence exists is measured by statistics that are used by the optimizer.

coded character set
A set of unambiguous rules that establishes a character set and the one-to-one relationships between the characters of the set and their coded representations.

coded character set identifier (CCSID)
A number that includes an encoding scheme identifier, character set identifiers, code page identifiers, and other information that uniquely identifies the coded graphic character representation.

code page
A set of assignments of characters to code points.

code point
In CDRA, a unique bit pattern that represents a character in a code page.

code set
Encoding values for a character set that provides the interface between the system and its input and output devices. ISO uses code set as the term equivalent to the IBM-defined term code page.

cold start
A system start, using an initial program load procedure. Contrast with warm start.

collating sequence
The sequence in which the characters are ordered for the purpose of sorting, merging, comparing, and processing indexed data sequentially.

collocated join
The result of two tables being joined in which:

column distribution value
Statistics describing the most frequent values of some column or the quantile values. These values are used in the optimizer to help determine the best access plan.

column function
An operation used in queries that applies to the values from several rows. Column functions include SUM, AVG, MIN, MAX, COUNT, STDDEV, and VARIANCE. Synonymous with aggregate function.

Command Line Processor (CLP)
A character-based interface for entering SQL statements and database manager commands.

commit
The operation that ends a unit of work by releasing locks so that the database changes made by that unit of work can be perceived by other processes. This operation makes the data changes permanent.

commit point
A point in time when data is considered to be consistent.

common critical section table
A replication control table at the source server that is used to establish concurrency control between the Capture and Apply programs and to prevent an update replication cycle.

Common Programming Interface Communications (CPI-C)
An API for applications that require program-to-program communication, making use of SNA's LU 6.2 to create a set of interprogram services.

common pruning control table
A replication control table at the source server that coordinates the pruning of the change data and unit-of-work control tables. The values in this table indicate how much data has been replicated by the Apply program and can be safely pruned by the Capture program.

common registrations table
A replication control table at the source server that relates each source table or view to an associated change data table and consistent change data table, if applicable.

common subscription columns table
A replication control table that contains column details of target tables.

common subscription events table
A replication control table that defines the events that trigger replication, including the event name and time.

common subscription set table
A replication control table that defines the members of a subscription set including the set name, Apply qualifier, source server, target server, and status.

common subscription statements table
A replication control table used to store the optional SQL statements that can be run at the beginning or end of the set subscription cycle.

common subscription targets member table
A replication control table that maps the source and target table relationships within a subscription set.

common table expression
An expression that defines a result table with a name (qualified SQL identifier) that can be specified as a table name in any FROM clause in the fullselect that follows the WITH clause.

comparison operator
An infix operator used in comparison expressions. Comparison operators are ¬< (not less than), <= (less than or equal to), ¬= (not equal to), = (equal to), >= (greater than or equal to), > (greater than), and ¬> (not greater than).

complete
A table attribute indicating that the table contains a row for every primary key value of interest. As a result, a complete source table can be used to perform a refresh of a target table.

composite key
A key composed of more than one column from a database table.

compound SQL statement
A block of SQL statements that are executed in a single call to the application server.

concurrency
The shared use of resources by multiple interactive users or application processes at the same time.

condensed
A table attribute indicating that the table contains current data rather than a history of changes to the data. A condensed table includes no more than one row for each primary key value in the table. As a result, a condensed table can be used to supply current information for a refresh.

conflict detection
The process of detecting an out-of-date row in a replica that was updated by a user application. When a conflict is detected, the transaction that caused the conflict is rejected. See also enhanced conflict detection, standard conflict detection.

connect
In DB2, to access objects at the database level.

connection
(1) An association between an application process and an application server.
(2) In data communications, an association established between functional units for conveying information.

connection handle
Within the CLI, the data object that contains information associated with a connection. This includes general status information, transaction status, and diagnostic information.

consistent change data (CCD) table
A replication table that is used for staging data, with four replication control columns. It can be one of the following types:

consolidation replication
A replication model in which the data from multiple source tables is replicated to a single target table. Contrast with fan-out replication.

constraint
A rule that limits the values that can be inserted, deleted, or updated in a table. See check constraint, referential constraint, and unique constraint.

container
See table space container.

contention
In the database manager, a situation in which a transaction attempts to lock a row or table that is already locked.

Control Center
A graphical interface that shows database objects (such as databases and tables) and their relationship to each other. From the Control Center you can perform the tasks provided by the DBA Utility, Visual Explain, and Performance Monitor tools.

control point
(1) In APPN, a component of a node that manages resources of that node and optionally provides services to other nodes in the network. Examples are a system services control point (SSCP) in a type 5 node, a physical unit control point (PUCP) in a type 4 node, a network node control point (NNCP) in a type 2.1 (T2.1) network node, and an end node control point (ENCP) in a T2.1 end node. An SSCP and an NNCP can provide services to other nodes.
(2) A component of a T2.1 node that manages the resources of that node. If the T2.1 node is an APPN node, the control point is capable of engaging in control point-to-control point sessions with other APPN nodes. If the T2.1 node is a network node, the control point also provides services to adjacent end nodes in the T2.1 network. See physical unit.

control privilege
The authority to completely control an object. This includes the authority to access, drop, or alter an object, and the authority to extend or revoke privileges on the object to other users.

control server
The database location of the applicable subscription definitions and apply trail table.

control table
A table in which replication source and subscription definitions or other replication control information is stored.

conversation
In APPC, a connection between two transaction programs over a logical unit-logical unit (LU-LU) session that allows them to communicate with each other while processing a transaction.

conversational transaction
In APPC, two or more programs communicating using the services of logical units (LUs).

conversation security
In APPC, a process that allows validation of a user ID or group ID and password before establishing a connection.

conversation security profile
The set of user IDs or group IDs and passwords that are used by APPC for conversation security.

Coordinated Universal Time (UTC)
Synonym for Greenwich Mean Time.

coordinating agent
The agent that is spawned when a request is received by the database manager from an application. It remains associated with the application during the life of the application. This agent coordinates subagents that work for the application. See also subagent.

coordinator node
The node to which the application originally connected and on which the coordinating agent resides.

coordinator subsection
The subsection of an application that starts other subsections (if any) and returns results to the application.

copy table
See target table.

correlated reference
Reference to a column of a table that is outside of a subquery.

correlated subquery
A subquery that contains a correlated reference to a column of a table that is outside of the subquery.

correlation name
An identifier designating a table or view within a single SQL statement. It can be defined in any FROM clause or in the first clause of an UPDATE or DELETE statement.

country code
When accessing the database, the country code of the application is used to determine the date and time presentation (display and print) formats. It is also used with the code page to determine the default collating sequence for the database.

CP
Control point.

CPI-C
Common Programming Interface Communications.

CPI-C side information profile
In SNA, the profile that specifies the conversation characteristics to use when allocating a conversation with a remote transaction program. The profile is used by local transaction programs that communicate through CPI Communications. It specifies the partner LU name (the name of the connection profile that contains the remote LU name), the mode name, and the remote transaction program name.

CP name
Control point name. A network-qualified name of a control point consisting of a network ID qualifier identifying the network to which the control point node belongs.

crash recovery
The process of recovering from an immediate failure.

CS
Cursor stability.

current function path
An ordered list of schema names used in the resolution of unqualified references to functions and data types. In dynamic SQL, the current function path is found in the CURRENT FUNCTION PATH special register. In static SQL, it is defined in the FUNCPATH option for PREP and BIND commands.

cursor
A named control structure used by an application program to point to a specific row within some ordered set of rows. The cursor is used to retrieve rows from a set. See also unambiguous cursor, ambiguous cursor.

cursor stability (CS)
An isolation level that locks any row accessed by a transaction of an application while the cursor is positioned on the row. The lock remains in effect until the next row is fetched or the transaction is terminated. If any data is changed in a row, the lock is held until the change is committed to the database.



D

DARI
Database Application Remote Interface. Former term for stored procedure.

data area
A memory area used by a program to hold information.

database administrator (DBA)
An individual responsible for the design, development, operation, safeguarding, maintenance, and use of a database. (T)

Database Application Remote Interface (DARI)
Former term for stored procedure.

database client
A workstation used to access a database residing on a database server.

database connection services (DCS) directory
A directory that contains entries for remote databases and the corresponding application requester used to access them.

database directory
A directory that contains database access information for all databases to which a client can connect.

database engine
The part of the database manager providing the base functions and configuration files needed to use the database.

database log
A set of primary and secondary log files consisting of log records that record all changes to a database. The database log is used to roll back changes for units of work that are not committed and to recover a database to a consistent state. See also primary log, secondary log.

database managed space (DMS) table space
A table space whose space is managed by the database. Contrast with system managed space (SMS) table space.

database management system (DBMS)
Synonym for database manager.

database manager
A computer program that manages data by providing the services of centralized control, data independence, and complex physical structures for efficient access, integrity, recovery, concurrency control, privacy, and security.

database manager instance
A logical database manager environment similar to an image of the actual database manager environment. You can have several instances of the database manager product on the same workstation. You can use these instances to separate the development environment from the production environment, tune the database manager to a particular environment, and protect sensitive information from a particular group of people.

database object
Anything that can be created or manipulated with SQL--for example, tables, views, indexes, packages, triggers, or table spaces.

database partition
A part of the database that consists of its own user data, indexes, configuration files, and transaction logs. Sometimes called a node or database node.

database server
A functional unit that provides database services for databases.

database system monitor
A collection of programming APIs that monitor performance and status information about the database manager, databases, and applications using the database manager and DB2 Connect.

data definition language (DDL)
A language for describing data and its relationships in a database. Synonymous with data description language. (T)

data description language
Synonym for data definition language. (T)

data enhancement
The modification of data as it is copied between the base table and the target table, including:

DataJoiner
A separately available product that provides client applications integrated access to distributed data and provides a single database image of a heterogeneous environment. With DataJoiner, a client application can join data that is distributed across multiple database management systems (using a single SQL statement) or update a single remote data source, as if the data were local.

data link control (DLC)
In SNA, the protocol layer that consists of the link stations that schedule data transfer over a link between two nodes and perform error control for the link.

data manipulation language (DML)
A subset of SQL statements used to manipulate data.

date
A three-part value that designates a day, month, and year.

date duration
A DECIMAL(8,0) value that represents a number of years, months, and days.

datetime value
A value of the data type DATE, TIME, or TIMESTAMP.

DB2 CLI
DB2 Call Level Interface. An alternative SQL interface for the DB2 family of products that takes full advantage of DB2 capability.

DB2 Connect
A product that provides the function necessary (DRDA application requester support) for client applications to read and update data stored in DRDA application servers, such as other members of the DB2 family.

DB2 SDK
DB2 Software Developer's Kit.

DB2 Software Developer's Kit (DB2 SDK)
A collection of tools that help developers create database applications.

DB2UEXIT
An optional, user-written executable program that the database manager invokes to move or retrieve archive log files.

DBA
Database administrator.

DBA Utility
A tool that lets DB2 users configure databases and database manager instances, manage the directories necessary for accessing local and remote databases, back up and recover databases or table spaces, and manage media on a system using a graphical interface. The tasks provided by this tool can be accessed from the Control Center.

DBCLOB
Double-byte character large object.

DBCS
Double-byte character set.

DBMS
Database management system.

DBMS instance connection
A logical connection between an application and an agent process or thread owned by a DB2 instance.

DCE**
Distributed Computing Environment.

DDL
Data definition language.

deadlock
A condition under which a transaction cannot proceed because it is dependent on exclusive resources that are locked by some other transaction, which in turn is dependent on exclusive resources in use by the original transaction.

deadlock detector
A process within the database manager that monitors the states of the locks to determine if a deadlock condition has occurred. When a deadlock condition is detected, the detector stops one of the transactions involved in the deadlock. This transaction is rolled back and the other transactions proceed.

delete rule
A rule associated with a referential constraint that either restricts the deletion of a parent row or specifies the effect of such a deletion on the dependent rows.

delimited identifier
A sequence of characters enclosed within quotation marks ("). The sequence must consist of a letter followed by zero or more characters, each of which is a letter, digit, or the underscore character.

delimiter
A character or flag that groups or separates items of data.

delimiter token
A string constant, a delimited identifier, an operator symbol, or any of the special characters shown in syntax diagrams.

dependent logical unit (DLU)
An LU that requires assistance from a system services control point (SSCP) to instantiate an LU-LU session.

dependent row
A row containing a foreign key that matches the value of a parent key in the parent row. The foreign key value thus represents a reference from the dependent row to the parent row.

dependent table
A table that is a dependent in at least one referential constraint.

descendent row
A row that is dependent on another row or a row that is a descendent of a dependent row.

descendent table
A table that is a dependent of another table or a descendent of a dependent table.

deterministic function
See not-variant function.

device name
A name reserved by the system, or a device driver that refers to a specific device.

directed join
A relational operation in which all of the rows in one or both of the joined tables are rehashed and directed to new database partitions based on the join predicate. If all of the partitioning key columns in a table participate in the equijoin predicates, the other table is rehashed; otherwise (if there is at least one equijoin predicate), both tables are rehashed.

directory services
A portion of the APPN protocols that maintains information about the location of resources in an APPN network.

distinct type
A user-defined data type that is internally represented as an existing type (its source type), but is considered to be a separate and incompatible type for semantic purposes.

Distributed Computing Environment (DCE**)
A set of services and tools that support the creation, use, and maintenance of distributed applications in a heterogeneous computing environment. DCE is independent of the operating system and network; it provides interoperability and portability across heterogeneous platforms.

distributed directory database
The complete listing of all the resources in the network as maintained in the individual directories scattered throughout an APPN network. Each node has a piece of the complete directory, but it is not necessary for any one node to have the entire list. Entries are created, modified, and deleted through system definition, operator action, automatic registration, and ongoing network search procedures. Synonymous with distributed network directory.

distributed network directory
Synonym for distributed directory database.

distributed relational database
A database whose tables are stored on different but interconnected computing systems.

Distributed Relational Database Architecture (DRDA)
Architecture that defines formats and protocols for providing transparent access to remote data. DRDA defines two types of functions, the application requester function and the application server function.

distributed unit of work (DUOW)
A unit of work that allows SQL statements to be submitted to multiple relational database management systems, but no more than one system per SQL statement.

DLC
Data link control.

DLU
Dependent logical unit.

DML
Data manipulation language.

DMS table space
Database managed space table space.

DNS
Domain name system.

Domain Name
A mechanism, in TCP/IP, that tracks the host names in a network. A domain name consists of a sequence of names separated by dots.

Domain Name System
The distributed database system used by TCP/IP to map human-readable machine names into IP addresses.

double-byte character large object (DBCLOB)
A sequence of double-byte characters, where the size can be up to 2 gigabytes. A data type that can be used to store large double-byte text objects. Also called double-byte character large object string. Such a string always has an associated code page.

double-byte character set (DBCS)
A set of characters in which each character is represented by two bytes.

DRDA
Distributed Relational Database Architecture.

DUOW
Distributed unit of work.

dynamic SQL
SQL statements that are prepared and run within a running program. In dynamic SQL, the SQL source is contained in host language variables rather than being coded into the program. The SQL statement might change several times while the program is running.



E

EBCDIC
Extended binary-coded decimal interchange code. A coded character set of 256 8-bit characters.

embedded SQL
SQL statements coded within an application program. See static SQL.

EN
End node.

encoding scheme
A set of rules to represent character data.

end node (EN)
In APPN, a node that supports sessions between its local control point (CP) and the CP in an adjacent network node.

enhanced conflict detection
Conflict detection that guarantees data integrity among all replicas and the origin table. The Apply program locks all replicas in the subscription set against further transactions, and begins detection after all changes made prior to locking have been captured. See also standard conflict detection, conflict detection.

environment handle
A handle that identifies the global context for database access. All data that is pertinent to all objects in the environment is associated with this handle.

equijoin
A join in which the predicate contains an equals operator. For example, T1.C1 = T2.C2.

EUC
Extended UNIX code.

event monitor
A database object for monitoring and collecting data on database activities over a period of time.

exclusive lock
A lock that prevents concurrently executing application processes from accessing database data.

executable statement
An SQL statement that can be embedded in an application program, dynamically prepared and executed, or issued interactively.

explain
To capture detailed information about the access plan that was chosen by the SQL compiler to resolve an SQL statement. The information describes the decision criteria used to choose the access plan.

explainable statement
An SQL statement for which the explain operation can be performed. Explainable statements are SELECT, UPDATE, INSERT, DELETE, and VALUES.

explained statement
An SQL statement for which an explain operation was performed.

explained statistics
Statistics for a database object that was referenced in an SQL statement at the time the statement was explained.

explain snapshot
A capture of the current internal representation of an SQL query and related information. This information is required by the Visual Explain tool.

export
To copy data from database manager tables to a file using formats such as PC/IXF, DEL, WSF, or ASC. Contrast with import.

exposed name
A correlation name, a table, or a view name specified in a FROM clause for which a correlation name is not specified.

Extended UNIX Code (EUC)
A protocol that can support sets of characters from 1 to 4 bytes in length. EUC is a means of specifying a collection of code pages rather than actually being a code page encoding scheme itself. This is the UNIX alternative to the PC double-byte (DBCS) code page encoding schemes.

extent
An allocation of space, within a container of a table space, to a single database object. This allocation consists of multiple pages.

extent map
A meta-data structure stored within a table space that records the allocation of extents to each object in the table space.

external source table
A non-DB2 table that is manually updated to match the consistent change data table structure and defined as a replication source. See also consistent change data (CCD) table.



F

fan-out replication
A replication model in which data from one source table is copied to multiple target tables, thereby distributing the data to multiple locations. Contrast with consolidation replication.

fast communication manager (FCM)
A group of functions that provide internodal communication support.

federated database system
A DB2 server and multiple data sources that the server sends queries to. In a federated data base system, a client application can join data that is distributed across multiple database management systems using a single SQL statement and view the data as if it were local.

fenced
A type of user-defined function or stored procedure that is defined to protect the DBMS from modifications by the function. The DBMS is isolated from the function or stored procedure by a barrier. Contrast with not-fenced.

file reference variable
A host variable that is used to indicate that data resides in a file on the client rather than in a client memory buffer.

file server
A workstation that runs the NetWare** operating system software and acts as a network server. DB2 uses the file server to store DB2 server address information, which a DB2 client retrieves to establish an IPX**/SPX client-server connection.

filter
A device or program that separates data, signals, or material in accordance with specified criteria. (A)

First Failure Service Log
A file (db2diag.log) that contains diagnostic messages, diagnostic data, alert information, and related dump information. This file is used by database administrators.

fixed-length string
A character or graphic string whose length is specified and cannot be changed. Contrast with varying-length string.

flagger
A precompiler option that identifies SQL statements in applications that do not conform to selected validation criteria (for example, the ISO/ANSI SQL92 Entry level standard).

foreign key
A key that is part of the definition of a referential constraint and that consists of one or more columns of a dependent table.

foreign update
An update that was applied to a target table and replicated to the local table.

forward recovery
A process used to roll forward a database or table space. It allows a restored database or table space to be rebuilt to a specified point in time by applying the changes recorded in the database log.

fullselect
A subselect, a values-clause, or a number of both that are combined by set operators.

fully qualified LU name
See network-qualified name.

function
A mapping, embodied as a program (the function body), invocable by means of zero or more input values (arguments) to a single value (the result).

function body
The piece of code that implements a function.

function family
A set of functions with the same function name. The context determines whether the usage refers to a set of functions within a particular schema, or all the relevant functions with the same name within the current function path.

function invocation
The use of a function together with any argument values being passed to the function body. The function is invoked by its name.

function path
An ordered list of schema names that restricts the search scope for unqualified function invocations and provides a final arbiter for the function selection process.

function path family
All the functions of the given name in all the schemas identified (or used by default) in the user's function path.

function resolution
The process, internal to the DBMS, for which a particular function instance is selected for invocation. The function name, the data types of the arguments, and the function path are used to make the selection. Synonymous with function selection.

function selection
Synonym for function resolution.

function shipping
The shipping of the subsections of a request to the specific node that contains the applicable data.

function signature
The logical concatenation of a fully qualified function name with the data types of all of its parameters. Each function in a schema must have a unique signature.



G

gap
A situation in which the Capture program is not able to read a range of log or journal records and there is potential loss of change data.

global table lock
A table lock that is acquired on all nodes in a table's nodegroup.

global transaction
A unit of work in a distributed transaction processing environment in which multiple resource managers are required.

grant
To give a privilege or authority to an authorization ID.

graphic character
Synonym for DBCS character.

graphic string
A sequence of DBCS characters.

group
A logical organization of users that have IDs according to activity or resource access authority.



H

handle
A variable that represents an internal structure within a software system.

hash partitioning
A partitioning strategy in which a hash function is applied to the partitioning key value to determine the database partition to which the row is assigned.

hop
In APPN, a portion of a route that has no intermediate nodes. A hop consists of only a single transmission group connecting adjacent nodes.

host computer
(1) In a computer network, a computer providing services such as computation, database access, and network control functions.
(2) The primary or controlling computer in a multiple computer installation.

host identifier
A name declared in the host program.

host language
Any programming language in which you can embed SQL statements.

host node
In SNA, a subarea node that contains a system services control point (SSCP); for example, an IBM System/390 computer with MVS and VTAM.

host program
A program written in a host language that contains embedded SQL statements.

host variable
In an application host program, a variable referenced by embedded SQL statements. Host variables are programming variables in the application program and are the primary mechanism for transmitting data between tables in the database and application program work areas.



I

identifier
One or more characters used to identify or name a data element and possibly to indicate certain properties of that data element. (A)

ILU
Independent logical unit.

import
To copy data from an external file, using formats such as PC/IXF, DEL, WSF or ASC, into database manager tables. Contrast with export.

import utility
Transactional utility that inserts user-supplied record data into a table.

independent logical unit (ILU)
An LU that is able to activate an LU-LU session without assistance from a system services control point (SSCP). It does not have an SSCP-LU session. Contrast with dependent logical unit.

index
A set of pointers that are logically ordered by the values of a key. Indexes provide quick access to data and can enforce uniqueness on the rows in the table.

index key
The set of columns in a table used to determine the order of index entries.

index partition
The part of an index that is associated with a table partition at a given node. An index defined on a table is implemented by multiple index partitions, one per table partition.

index sargable predicates
Predicates that are applied to index entries, in index leaf pages, to reduce the number of index entries that qualify the SQL request. This helps reduce the number of data rows accessed.

indicator variable
A variable used to represent the null value in an application program. If the value for the selected column is null, a negative value is placed in the indicator variable.

indoubt transaction
Pertains to a transaction in which one phase of a two-phase commit completes successfully but the system fails before a subsequent phase can complete.

initialization fullselect
The first fullselect in a recursive common table expression that gets the direct children of the initial value from the source table.

inner join
A join method in which a column that is not common to all of the tables being joined is dropped from the resultant table. Contrast with outer join.

inoperative package
A package that cannot be used because one or more functions that it depends on have been dropped. Such a package must be explicitly rebound. Contrast with invalid package.

inoperative trigger
A trigger that is no longer usable. A trigger will be marked inoperative when an object on which it depends is dropped (or made inoperative) or a privilege on which it depends is revoked.

inoperative view
A view that is no longer usable. A view will be marked as inoperative when either:

insert rule
A condition enforced by the database manager that must be met before a row can be inserted into a table.

instance
See database manager instance.

intermediate network node
In APPN, a node that is part of a route between an origin LU (OLU) and a destination LU (DLU) but that neither contains the OLU or the DLU nor serves as the network server for either the OLU or DLU.

internal CCD table
A consistent change data table that is a join of the change data table and the unit-of-work table at the source server.

Internet Protocol (IP)
A protocol used to route data from its source to its destination in an Internet environment.

Internetwork Packet Exchange** (IPX**)
A connectionless datagram protocol, used in a NetWare** LAN environment, to transfer data to a remote node. IPX makes a best-effort attempt to send data packets, but does not guarantee reliable delivery of the data.

inter-partition parallelism
Refers to the ability to perform multiple database operations (such as index creation, database load, and SQL queries) at the same time across multiple partitions of a partitioned database. Contrast with intra-partition parallelism.

Inter-Process Communication (IPC)
A mechanism of an operating system that allows processes to communicate with each other.

intra-partition parallelism
Refers to the ability to perform multiple database operations (such as index creation, database load, SQL queries) at the same time within a single database partition. Contrast with inter-partition parallelism.

intra-query parallelism
Processing parts of a single query at the same time using either intra-partition parallelism, inter-partition parallelism, or both.

invalid package
A package that becomes invalid when an object that the package depends on is dropped. (The object is of a type other than function; for example, index.) Such a package is implicitly rebound upon invocation. Contrast with inoperative package.

I/O parallelism
See parallel I/O.

IP
Internet Protocol.

IPX**
Internetwork Packet Exchange**.

isolation level
An attribute that defines the degree to which an application process is isolated from other concurrently executing application processes.



J

job scheduler
A program used to automate certain tasks for running and managing database jobs.

join
A relational operation that allows for retrieval of data from two or more tables based on matching column values.



K

key
A column or an ordered collection of columns that are identified in the description of a table, index, or referential constraint.

key-value based partitioning strategy
A strategy for assigning rows in a table to database partitions. Rows are assigned based on the values of the partitioning key columns.

keyword
One of the predefined words of a computer, command language, or an application.



L

labeled duration
A number that represents a duration of years, months, days, hours, minutes, seconds, or microseconds.

large object (LOB)
A sequence of bytes, where the length can be up to 2 gigabytes. It can be any of three types: BLOB (binary), CLOB (single-byte character or mixed) or DBCLOB (double-byte character).

length attribute
A value associated with a string that represents the declared fixed length or maximum length of the string.

LEN node
Low-entry networking node.

list prefetch
An access method that takes advantage of prefetching even in queries that do not access data sequentially. This is done by scanning the index and collecting RIDs in advance of accessing any data pages. These RIDs are then sorted, and data is prefetched using this list.

load copy
A backup image of data that was loaded at a previous time and can be restored during roll-forward recovery.

load utility
A nontransactional utility that performs block updates of table data. Contrast with import utility.

LOB
Large object.

LOB locator
A mechanism that allows an application program to manipulate a large object value in the database system. A LOB locator is a simple token value that represents a single LOB value. An application program retrieves a LOB locator into a host variable and can then apply SQL functions to the associated LOB value via the locator.

local database
A database that is physically located on the workstation in use. Contrast with remote database.

local database directory
A directory where a database physically resides. Databases that are displayed in the local database directory are located on the same node as the system database directory.

local table lock
A table lock that is acquired only on a single database partition.

local update
An update to the base table, not to the replica.

locator
See LOB locator.

lock
(1) A means of serializing events or access to data.
(2) A means of preventing uncommitted changes made by one application process from being perceived by another application process and for preventing one application process from updating data that is being accessed by another process.

lock escalation
In the database manager, the response that occurs when the number of locks issued for one agent exceeds the limit specified in the database configuration; the limit is defined by the MAXLOCKS configuration parameter. During a lock escalation, locks are freed by converting locks on rows of a table into one lock on a table. This is repeated until the limit is no longer exceeded.

locking
The mechanism used by the database manager to ensure the integrity of data. Locking prevents concurrent users from accessing inconsistent data.

log
(1) See database log.
(2) A file used to record changes made in a system.

log head
The oldest written log record in the active log.

logical node
A node on a processor when more than one node is assigned to that processor. See also node.

logical operator
A keyword that specifies how multiple search conditions are to be evaluated (AND, OR) or if the logical sense of a search condition is to be inverted (NOT).

logical unit (LU)
In SNA, a port through which an end user accesses the SNA network to communicate with another end user. An LU may be capable of supporting many sessions with other LUs.

logical unit 6.2 (LU 6.2)
The LU type that supports sessions between two applications using APPC.

log partition
The log file on each database partition that records database activity for that database partition.

log record
A record of an update to a database performed during a unit of work. This record is written after the log tail of the active log.

log tail
The log record that was written most recently in an active log.

long string
A varying-length string whose maximum length is greater than 254 bytes.

long table space
A table space that can store only long string or large object (LOB) data.

low-entry networking node (LEN node)
A type 2.1 node that supports independent LU protocols but does not support CP-CP sessions. It can be a peripheral node attached to a boundary node in a subarea network, an end node attached to an APPN network node in an APPN network, or a peer-connected node directly attached to another LEN node or APPN end node.

LU
Logical unit.

LU 6.2
See logical unit 6.2.

LU type
The classification of a logical unit in terms of the specific subset of SNA protocols and options it supports for a given session, specifically:



M

mapped conversation
In APPC, a conversation between two transaction programs (TPs) using the APPC mapped conversation API. In typical situations, end-user TPs use mapped conversation and service TPs use basic conversations. However, either type of program can use either type of conversation. Contrast with basic conversation.

masking character
A character used to represent optional characters at the front, middle, and end of a search term. Masking characters are normally used for finding variations of a term in a precise index.

MBCS
Multi-byte character set.

migration
(1) The process of moving data from one computer system to another without converting the data.
(2) Installation of a new version or release of a program to replace an earlier version or release.

mixed-character string
A string containing a mixture of single-byte and multi-byte characters.

mixed-data string
Synonym for mixed-character string.

mobile client
The node, usually a lap top computer, where the mobile enabler and replication source and target tables used in a mobile environment are located. The mobile replication mode is invoked from the mobile client.

mobile replication enabler
A replication program that starts the mobile replication mode at the mobile client.

mobile replication mode
A mode of replication in which the Capture and Apply programs operate as needed rather than autonomously and continuously. This mode is invoked from the mobile client and allows data to be replicated when the mobile client is available for a connection to the source or target server.

modelled statistics
Statistics for a database object that may or may not be referenced in an SQL statement, yet currently exist in an explain model. The object may or may not currently exist in the database.

mode name
In APPC, the name used by the initiator of a session to designate the characteristics desired for the session, such as message length limits, sync point, class of service within the transport network, and session routing and delay characteristics.

monitoring session
The act of monitoring a database manager or of playing back information from a previously monitored database manager. The DB2 Performance Monitor is used for creating a monitoring session and for selecting which database objects to monitor.

monitor switch
Database manager parameters manipulated by the user to control the type of information and the quantity of information returned in performance snapshots.

multi-byte character set (MBCS)
A set of characters in which each character is represented by two or more bytes. Those using only two bytes are more commonly known as double-byte character sets.

multitasking
A mode of operation that provides for concurrent performance, or interleaved execution of two or more tasks. (I) (A)



N

NAU
Network addressable unit.

NDS
Network Directory Services.

nested table expression
A result table obtained directly or indirectly from one or more other tables through the evaluation of a fullselect that is specified in the FROM clause.

NETID
Network identifier. Synonym for network name.

network address
An identifier for a node in a network.

network addressable unit (NAU)
A logical unit (LU), physical unit (PU), control point (CP), or system services control point (SSCP). It is the origin or the destination of information transmitted by the path control network. See also network name.

Network Directory Services (NDS)
A global, distributed, replicated database introduced in NetWare** Version 4.0 that maintains information about, and provides access to, every resource on the network. The NetWare Directory database organizes objects, independent of their physical location, in a hierarchical tree structure called the directory tree.

network name
In SNA, a symbolic name by which end users refer to a network addressable unit (NAU), a link station, or a link. Synonymous with NETID.

network node (NN)
In APPN, a node on the network that provides distributed directory services, topology database exchanges with other APPN network nodes, and session and routing services. Synonym for APPN network node.

network node server
An APPN network node that provides network services for its local logical units and adjacent end nodes.

network-qualified name
The name by which an LU is known throughout an interconnected SNA network. A network-qualified name consists of a network name identifying the individual subnetwork, and a network LU name. Network-qualified names are unique throughout an interconnected network. Also known as the network-qualified LU name, or fully qualified LU name.

network services
The services within network addressable units that control network operation through SSCP-SSCP, SSCP-PU, SSCP-LU, and CP-CP sessions.

nickname
An identifier that a federated server uses to reference a data source table or view.

NN
Network node.

node
(1) In database partitioning, synonymous with database partition.
(2) In hardware, a uniprocessor or symmetric multiprocessor (SMP) computer that is part of a clustered system or a massively parallel processing (MPP) system. For example, RS/6000 SP is an MPP system that consists of a number of nodes connected by a high-speed network.
(3) In communications, an end point of a communications link, or a junction common to two or more links in a network. Nodes can be processors, communication controllers, cluster controllers, terminals, or workstations. Nodes can vary in routing and other functional capabilities.

node directory
A directory that contains information necessary to establish communications from a client workstation to all applicable database servers.

nodegroup
A named group of one or more database partitions.

noncondensed attribute
A table attribute indicating that the table contains a history of changes to the data, not current data. A table that has this attribute set includes more than one row for each key value.

nondelimited ASCII (ASC) format
A file format used to import data. Nondelimited ASCII is a sequential ASCII file with row delimiters used for data exchange with any ASCII product.

normalization
In databases, the process of restructuring a data model by reducing its relations to their simplest forms. (T)

not-fenced
A type of user-defined function or stored procedure that is defined to be run in the DBMS process. Contrast with fenced.

not-variant function
A user-defined function whose result is solely dependent on the values of the input arguments. Successive invocations with the same argument values always produce the same results. Contrast with variant function.

nullable
The condition where a value for a column, function parameter, or result can have an absence of a value. For example, a field for a person's middle initial does not require a value.

null value
A parameter position for which no value is specified.



O

object
(1) Anything that can be created or manipulated with SQL--for example, tables, views, indexes, or packages.
(2) In object-oriented design or programming, an abstraction consisting of data and operations associated with that data.
(3) For NetWare**, an entity that is defined on the network and thus given access to the file server.

object property
A property that identifies a category of information associated with an object. A NetWare** bindery object can be assigned one or more properties. The DB2 server instance object has an object property NET_ADDR, which denotes the location of the record within the object.

object type
(1) A 2-byte number that classifies an object in the bindery on a NetWare** file server. 062B represents the DB2 database server object type.
(2) A categorization or grouping of object instances that share similar behaviors and characteristics.

ODBC
Open Database Connectivity.

ODBC driver
A driver that implements ODBC function calls and interacts with a data source.

offline backup
A backup of the database or table space that was made when the database or table space was not being accessed by applications. The Backup Database utility acquires exclusive use of the database until the backup is complete. Contrast with online backup.

offline restore
A restoration of a copy of a database or table space from a backup. The Backup Database utility has exclusive use of the database until the restore is completed.

online backup
A backup of the database or table space that is made while the database or table space is being accessed by other applications. Contrast with offline backup.

online monitor
See Performance Monitor.

online restore
A restoration of a copy of a database or table space while the database or table space is being accessed by other applications. Contrast with offline restore.

Open Database Connectivity (ODBC)
An API that allows access to database management systems using callable SQL, which does not require the use of a SQL preprocessor. The ODBC architecture allows users to add modules, called database drivers, that link the application to their choice of database management systems at run time. Applications do not have to be linked directly to the modules of all the supported database management systems.

operand
An entity on which an operation is performed.

optimized SQL text
SQL text, produced by the Explain facility, based on the query actually used by the optimizer to choose the access plan. This query has been supplemented and rewritten by the various components of the SQL compiler during statement compilation. The text has been reconstructed from its internal representation, and differs from the original SQL text. The optimized statement produces the same result as the original statement.

optimizer
A component of the SQL compiler that chooses an access plan for a DML statement by modelling the execution cost of many alternative access plans and choosing the one with the minimal estimated cost.

ordinary identifier
In SQL, a letter, which might be followed by zero or more characters, each of which is a letter (a-z and A-Z), a symbol, a number, or the underscore character, used to form a name.

ordinary token
A numeric constant, an ordinary identifier, a host identifier, or a keyword.

outer join
A join method in which a column that is not common to all of the tables being joined becomes part of the resultant table. Contrast with inner join.

output file
A database or device file that is opened with the option to allow the writing of records.

overflow record
(1) On an indirectly addressed file, a record whose key is randomized to the address of a full track or to the address of a home record.
(2) In DB2, an updated record that is too large to fit on the page it is currently stored in. The record is copied to a different page and its original location is replaced with a pointer to the new location.
(3) In Database Monitor, a record inserted in the event monitor data stream to indicate that records were discarded because the named pipe was full and records were not processed in time. An overflow record indicates how many records were discarded.

overloaded function name
A function name for which there are multiple functions within a function path or schema. Those within the same schema must have different signatures.



P

package
A control structure produced during program preparation that is used to execute SQL statements.

packet
In data communication, a sequence of binary digits, including data and control signals, that is transmitted and switched as a composite whole.

page
A block of storage within a table or index whose size is 4096 bytes (4 K).

parallel I/O
Refers to the process of reading from or writing to two or more I/O devices at the same time to reduce response time.

parallelism
The ability to perform multiple database operations at the same time (in parallel). See inter-partition parallelism, intra-partition parallelism, and parallel I/O.

parallel session
In SNA, two or more concurrently active sessions between the same two logical units (LUs). Each session can have different session parameters. Contrast with session.

parameterized data type
A data type that can be defined with a specific length, scale, or precision. These are the string and decimal data types.

parameter marker
A question mark (?) that appears in a statement string of a dynamic SQL statement. The question mark can appear where a host variable could appear if the statement string was a static SQL statement.

parent key
A primary key or unique key that is used in a referential constraint. The values of a parent key determine the valid values of the foreign key in the constraint.

parent row
A row that has at least one dependent row.

parent table
A table that is a parent in at least one referential constraint.

partition compatible join
A join where all of the rows that are joined reside in the same database partition.

partitioned database
A database with two or more database partitions. Data in user tables can be located in one or more database partitions. When a table is on multiple partitions, some of its rows are stored in one partition and others are stored in other partitions. See database partition.

partitioning function
A function that takes a partitioning key value of a row as input and produces a partition number as output.

partitioning key
(1) An ordered set of one or more columns in a given table. For each row in the table, the values in the partitioning key columns are used to determine on which database partition the row belongs.
(2) In replication, an ordered set of one or more columns in a given table. For each row in the source table, the values in the partitioning key columns are used to determine in which target table the row belongs.

partitioning map
A vector of partition numbers that maps a partitioning map index to database partitions in the nodegroup.

partitioning map index
A number assigned to a hash partition or range partition.

partner logical unit (LU)
In SNA, the remote participant in a session.

peer-to-peer communication
Communication between two SNA logical units (LUs) that is not managed by a host; commonly used when referring to LU 6.2 nodes.

performance metrics
A collection of all performance variables belonging to the same database object.

Performance Monitor
A tool that lets database administrators use a graphical interface to monitor the performance of a DB2 system for tuning purposes. The tasks provided by this tool can be accessed from the Control Center.

performance snapshot
Performance data for a set of database objects that is retrieved from the database manager at a point in time.

performance variable
A statistic derived from performance data obtained from the database manager. The expression for this variable can be user-defined.

performance variable profile
A flat file that contains definitions of performance variables. This file can be edited, copied, and shared. Different profiles can be used by the same Performance Monitor so that different calculations can be performed.

phantom row
A table row that can be read by application processes that are executing with any isolation level except repeatable read. When an application process issues the same query multiple times within a single unit of work, additional rows can appear between queries because of the data being inserted and committed by application processes that are running concurrently.

physical unit
The component that manages and monitors the resources (such as attached links and adjacent link stations) associated with a node, as requested by an SSCP through an SSCP-PU session. An SSCP activates a session with the PU in order to indirectly manage, through PU, resources of the node such as attached links. This term applies to types 2.0, 4, and 5 nodes only. See also control point.

point-in-time table
A type of target table whose content matches all or part of a source table, with an added system column that identifies the approximate time when the particular row was inserted or updated at the source system.

point of consistency
A point in time when all the recoverable data a program accesses is consistent. The point of consistency occurs when updates, inserts, and deletions are either committed to the physical database or rolled back. Synonym for commit point and sync point. See also rollback.

precision
In numeric data types, the total number of binary or decimal digits excluding the sign.

precompile
To process programs containing SQL statements before they are compiled. SQL statements are replaced with statements that will be recognized by the host language compiler. The output from a precompile includes source code that can be submitted to the compiler and used in the bind process.

predicate
An element of a search condition that expresses or implies a comparison operation.

prefetch
To read data ahead of, and in anticipation of, its use.

prepare
To convert an SQL statement from text form to an executable form, by submitting it to the SQL compiler.

primary key
A unique key that is part of the definition of a table. A primary key is the default parent key of a referential constraint definition.

primary log
A set of one or more log files used to record changes to a database. Storage for these files is allocated in advance. Contrast with secondary log.

privilege
The right to access a specific database object in a specific way. These rights are controlled by users with SYSADM (system administrator) authority or DBADM (database administrator) authority or by creators of objects. Privileges include rights such as creating, deleting, and selecting data from tables.

procedure
Synonym for stored procedure.

protocol.ini
A file that contains LAN configuration and binding information for all the protocol and medium access control (MAC) system modules.

PU
Physical unit.

public authority
The authority for an object granted to all users.

PU type
In SNA, the classification of a physical unit (PU) according to the type of node on which it resides.



Q

quantified predicate
A predicate that compares a value with a set of values.

query
A request for information from the database based on specific conditions; for example, a request for a list of all customers in a customer table whose balance is greater than $1000.

quiesce
To end a process by allowing operations to complete normally, while rejecting any new requests for work.

quoted name
Synonym for delimited identifier.



R

RDBMS
Relational database management system.

read stability (RS)
An isolation level that locks only those rows that an application retrieves within a transaction. It ensures that any qualifying row read during a transaction is not changed by other application processes until the transaction is completed, and that any row changed by another application process is not read until the change is committed by that process. Read stability allows more concurrency than repeatable read, and less than cursor stability.

rebind
To create a new package for an application program that was previously bound. For example, if an index is added for a table accessed by a program, the package must be rebound for it to take advantage of the new index.

record
The storage representation of a single row of a table.

recording
The information from performance snapshots that can be viewed at a later time.

recoverable log
A database log in which all log records are retained so that, in the event of a failure, lost data can be recovered during forward recovery. Contrast with circular log.

recovery
(1) The act of resetting a system, or data that is stored in a system, to an operable state following damage.
(2) The process of rebuilding databases by restoring a backup and rolling forward the logs associated with it.

recovery log
See database log.

recovery pending
A state of the database or table space. A database or table space is put in recovery pending state when it is restored from a backup. While the database or table space is in this state, its data cannot be accessed.

recursion cycle
The cycle that occurs when a fullselect within a common table expression includes the name of the common table expression in a FROM clause.

recursive common table expression
A common table expression that refers to itself in a FROM clause from the fullselect. Recursive common table expressions are used to write recursive queries.

recursive query
A fullselect that uses a recursive common table expression.

referential constraint
The referential integrity rule that the nonnull values of the foreign key are valid only if they also appear as values of a parent key.

referential integrity
The state of a database in which all values of all foreign keys are valid.

refresh
A process in which all of the data of interest in a user table is copied to the target table, replacing existing data.

regular table space
A table space that can store any nontemporary data.

rejected transaction
A transaction containing one or more updates from replica tables that are out of date in comparison to the origin table.

relational database
A database that can be perceived as a set of tables and manipulated in accordance with the relational model of data.

remote database
A database that is physically located on a workstation other than the one in use. Contrast with local database.

remote unit of work (RUOW)
A unit of work that allows for the remote preparation and execution of SQL statements.

repeatable read (RR)
An isolation level that locks all the rows in an application that are referenced within a transaction. When a program uses repeatable read protection, rows referenced by the program cannot be changed by other programs until the program ends the current transaction.

replica
A type of target table that can be updated locally and receives updates from a user table through a subscription definition. It can be a source for updating the user table or read-only target tables.

replication
The process of taking changes that are stored in the database log or journal at the source server and applying them to the target server.

replication administrator
The user responsible for defining replication sources and subscriptions. This user can also run the Capture and Apply programs.

replication source
A database table that is defined as a source for replication. This type of table can accept copy requests and is the source table in a replication subscription set.

replication subscription
A specification for copying changed data from replication sources to target tables at a specified time and frequency, with the option of enhancing data. It defines all of the information that is required by the Apply program to copy data.

reserved word
(1) In programming languages, a keyword that may not be used as an identifier. (I)
(2) A word used in a source program to describe an action to be taken by the program or compiler. It must not appear in the program as a user-defined name or a system name.
(3) A word that has been set aside for special use in the SQL standard.

restore
To return a backup copy to the active storage location for use.

restore set
A backup copy of a database or table space plus zero or more log files that, when restored and rolled forward, bring the database or table space back to a consistent state.

result set
Synonym for result table.

result table
The set of rows produced by the evaluation of a SELECT statement. Synonymous with result set.

revoke
To remove a privilege or authority from an authorization ID.

RID (Record ID)
A number that is used internally by DB2 to uniquely identify a record in a table. It contains enough information to address the page in which the record is stored.

rollback
The process of restoring data changed by SQL statements to the state at its last commit point. See also point of consistency.

roll-forward
The process of updating the data in a restored database by applying changes recorded in the database log. See forward recovery.

row
The horizontal component of a table consisting of a sequence of values, one for each column of the table.

RR
Repeatable read.

RS
Read stability.

RUOW
Remote unit of work.



S

sargable
A predicate that can be evaluated as a search argument. See predicate.

SBCS
Single-byte character set.

scalar fullselect
A fullselect that returns a single value-- one row of data consisting of exactly one column.

scalar function
An SQL operation that produces a single value from another value and is expressed as a function name followed by a list of arguments enclosed in parentheses.

scale
The number of digits in the fractional part of a number.

schema
A collection of database objects such as tables, views, indexes, or triggers. It provides a logical classification of database objects.

SDK
Software Developer's Kit.

search condition
A criterion for selecting rows from a table. A search condition consists of one or more predicates.

secondary log
A set of one or more log files used to record changes to a database. Storage for these files is allocated as needed when the primary log is full.

self-referencing row
A row that is a parent of itself.

self-referencing subquery
A subselect or fullselect within a DELETE, INSERT, or UPDATE statement that refers to the same table that is the object of the SQL statement.

self-referencing table
A table that is both a parent and a dependent table in the same referential constraint.

server
(1) In a network, a node that provides facilities to other stations; for example, a file server, a printer server, a mail server.

(2) In a federated system, a unit of information that identifies a data source to a federated server. This information can include the server's name, its type, its version, and the name of the wrapper that the federated server uses to communicate with and retrieve data from the data source.

service name
A name that provides a symbolic method of specifying the port number to be used at a remote node. The TCP/IP connection requires:

session
A logical connection between two stations or SNA network addressable units (NAUs) that allows the two stations or NAUs to communicate.

session limit
In SNA, the maximum number of concurrently active logical unit-logical unit (LU-LU) sessions that a particular logical unit (LU) can support.

session partner
In SNA, one of the two network addressable units (NAUs) participating in an active session.

session security
For LU 6.2, partner LU verification and session data encryption. A Systems Network Architecture (SNA) function that allows data to be transmitted in encrypted form.

set operator
The SQL operators UNION, EXCEPT, and INTERSECT corresponding to the relational operators union, difference, and intersection. A set operator derives a result table by combining two other result tables.

shadowing
A recovery technique in which current page contents are never overwritten. Instead, new pages are allocated and written while the pages whose values are being replaced are retained as shadow copies until they are no longer needed to support the restoration of the system state due to a transaction rollback.

share lock
A lock that limits concurrently executing application processes to read-only operations on database data.

short string
A fixed-length string or a varying-length string whose maximum length is less than or equal to 254 bytes.

single-byte character set (SBCS)
A character set in which each character is represented by a one-byte code. Contrast with double-byte character set, multi-byte character set.

SMS table space
System managed space table space.

SNA
Systems Network Architecture.

SNA network
The part of the user application network that conforms to the formats and protocols of Systems Network Architecture (SNA). It enables reliable transfer of data among users and provides protocols for controlling the resources of various network configurations. The SNA network consists of network addressable units (NAUs), gateway function, intermediate session routing function components, and the transport network.

snapshot
See performance snapshot, explain snapshot.

Performance Monitor
An API used to assess the status of the database manager, individual databases, tables, table spaces, and individual applications.

soft checkpoint
The process of writing some information to the log file header; this information is used to determine the starting point in the log in case a database restart is required.

Software Developer's Kit (SDK)
An application development product that allows applications to be developed on a client workstation to access remote database servers including host relational databases through the DB2 Connect products.

source function
A user-defined function (UDF) whose body is used to implement one or more other UDFs.

source server
The database location of the replication source and the Capture program.

source table
A table that contains the data that is to be copied to a target table. The source table can be a replication source table, a change data table, or a consistent change data table. Contrast with target table.

source type
An existing type that is used to internally represent a distinct type.

special register
A storage area that is defined for an application process by the database manager and is used to store information that can be referenced in SQL statements. Examples are USER and CURRENT DATE.

specific function name
The name that uniquely identifies a function to the system.

SQL
A standardized language for defining and manipulating data in a relational database.

SQLCA
SQL communication area.

SQL communication area (SQLCA)
A set of variables that provides an application program with information about the execution of its SQL statements or its requests from the database manager.

SQLDA
SQL descriptor area.

SQL descriptor area (SQLDA)
A set of variables that is used in the processing of certain SQL statements. The SQLDA is intended for dynamic SQL programs.

SSCP
System services control point.

stack
An area in memory that stores temporary register information, parameters, and return addresses of subroutines.

staging table
A consistent change target table that is used as the source for updating data to multiple target tables.

standard conflict detection
Conflict detection in which the Apply program searches for conflicts in rows that are already captured in the replica's change data tables. See also conflict detection, enhanced conflict detection.

statement
An instruction in a program or procedure.

statement handle
In CLI, a handle that refers to the data object that contains information about an SQL statement. This includes information such as dynamic arguments, bindings for dynamic arguments and columns, cursor information, result values, and status information. Each statement handle is associated with a connection handle.

static SQL
SQL statements that are embedded within a program, and are prepared during the program preparation process before the program is executed. After being prepared, a static SQL statement does not change, although values of host variables specified by the statement may change.

stored procedure
A block of procedural constructs and embedded SQL statements that is stored in a database and can be called by name. Stored procedures allow an application program to be run in two parts. One part runs on the client and the other on the server. This allows one call to produce several accesses to the database. Synonymous with procedure.

string
In programming languages, the form of data used for storing and manipulating text.

Structured Query Language
See SQL.

subagent
A type of agent that works on subrequests. A single application can make many requests, and each request can be broken into many subrequests. Therefore, there can be multiple subagents working on behalf of the same application. All subagents working for the application are coordinated by the coordinating agent for that application. See also coordinating agent.

subordinate agent
See subagent.

subquery
A fullselect used within a search condition of an SQL statement.

subscription cycle
The processing of a subscription set by the Apply program.

subscription set
The specification of a group of source tables, target tables, and the control information that governs the replication of changed data. Updates are committed in the same transaction.

subselect
That form of a query that does not include an ORDER BY clause, an UPDATE clause, or UNION operators.

symbolic destination name
Specifies the name of a remote partner. The name corresponds to an entry in the CPI Communications side information table that contains the necessary information (partner LU name, mode name, partner TP name) for the client to set up an APPC connection to the server.

synchronization level
In APPC, the specification indicating whether the corresponding transaction programs exchange confirmation requests and replies.

synchronous
Pertaining to two or more processes that depend upon the occurrences of specific events, such as a common timing signal. Contrast with asynchronous.

sync point
Synonym for point of consistency.

system catalog
See catalog.

system database directory
A directory that contains entries for every database that can be accessed using the database manager. It is created when the first database is created or cataloged on the system.

system managed space (SMS) table space
A table space whose space is managed by the operating system. This storage model is based on files created under subdirectories, and managed by the file system. Contrast with database managed space (DMS) table space.

system services control point (SSCP)
The control point in a SNA network that provides network services for dependent nodes.

Systems Network Architecture (SNA)
The description of the logical structure, formats, protocols, and operational sequences for transmitting information units through the networks and also the operational sequences for controlling the configuration and operation of networks.



T

table
A named data object consisting of a specific number of columns and some unordered rows.

table designator
A column name qualifier that designates a specific object table.

table queue
A mechanism for transferring rows between database nodes. Table queues are distributed row streams with simplified rules for the insertion and removal of rows. Table queues can also be used to deliver rows between different processes in the serial database.

table space
An abstraction of a collection of containers into which database objects are stored. A table space provides a level of indirection between a database and the tables stored within the database. A table space:

See also system managed space (SMS) table space, database managed space (DMS) table space, long table space, regular table space, temporary table space.

table space container
A generic term describing an allocation of space to a table space. Depending on the table space type, the container can be a directory, device, or file.

target server
The database location of the target table. Normally this is also the location of the Apply program.

target table
The table on the target server to which data is copied. It can be a user copy table, a point-in-time table, a base aggregate table, a change aggregate table, a consistent change data table, or a replica table.

TCP/IP
Transmission Control Protocol/Internet Protocol.

temporary table
A table created during the processing of an SQL statement to hold intermediate results.

temporary table space
A table space that can store only temporary tables.

territory
A portion of the POSIX** locale that is mapped to the country code for internal processing by the database manager.

thread
In some operating systems, the smallest unit of operation to be performed in a process.

threshold trigger
An event occurring when the value of a performance variable exceeds or falls below a user-defined threshold value. The action that occurs as a result of a threshold trigger could be:

time
A three-part value that designates a time of day in hours, minutes, and seconds.

time duration
A DECIMAL(6,0) value that represents a number of hours, minutes, and seconds.

timeron
A unit of measurement used to give a rough relative estimate of the resources, or cost, required by the database server to execute two plans for the same query. The resources calculated in the estimate include weighted CPU and I/O costs.

timestamp
A seven-part value that consists of a date and time expressed in years, months, days, hours, minutes, seconds, and microseconds.

timestamp duration
A DECIMAL(20,6) value that represents a number of years, months, days, hours, minutes, seconds, and microseconds.

TM Database
Transaction Manager Database.

TP
Transaction program.

token
The basic syntactic unit of a computing language. A token consists of one or more characters, excluding the blank character, and excluding characters within a string constant or delimited identifier.

topology and routing services (TRS)
An APPN control point component that manages the topology database and computes routes.

trace table
A table that contains a high-level record of the execution of the Capture program.

transaction
An exchange between a workstation and a program, two workstations, or two programs that accomplish a particular action or result. An example is the entry of a customer's deposit and the update of the customer's balance. Synonym for unit of work.

transaction compensation
A process that restores rows that are affected by a committed transaction that is rejected. When a committed transaction is rejected, the rows are restored to the state that they were in before the transaction was committed.

transaction manager
Assigns identifiers to transactions, monitors their progress, and takes responsibility for transaction completion and failure recovery.

Transaction Manager Database (TM Database)
A database that is used to log transactions when a two-phase commit (SYNCPOINT TWOPHASE) is used with DB2 databases. In the event of transaction failure, the TM Database information can be accessed to resynchronize databases involved in the failed transaction.

transaction program (TP)
An application program that uses APPC to communicate with a partner application program.

transition table
A named temporary table that contains the transition values for each row affected by the triggering modification. An old transition table contains the values of affected rows before the modification is applied, and a new transition table contains the values of the affected rows after the modification is applied.

transition variable
A variable that is valid only in FOR EACH ROW triggers. It allows access to the transition values for the current row. An old transition variable is the value of the row before the modification is applied, and the new transition variable is the value of the row after the modification is applied.

Transmission Control Protocol/Internet Protocol (TCP/IP)
A set of communications protocols that provide peer-to-peer connectivity functions for both local and wide area networks.

trigger
In DB2, an object in a database that is invoked indirectly by the database manager when a particular SQL statement is run.

triggered action
The action that is executed when the trigger event occurs.

triggered-action condition
The search condition that controls the execution of the SQL statements within the triggered action.

trigger event
In a trigger definition, an update operation (INSERT, UPDATE, or DELETE statement) that causes the trigger to be run.

truncation
The process of discarding part of a result from an operation when it exceeds memory or storage capacity.

tuning parameters table
A table at the source server that contains timing information used by the Capture program. The information includes:

two-phase commit
A two-step process by which recoverable resources and an external subsystem are committed. During the first step, the database manager subsystems are polled to ensure that they are ready to commit. If all subsystems respond positively, the database manager instructs them to commit.

typed parameter marker
A parameter marker that is specified along with its target data type. It has the general form: 
CAST(? AS data-type)



U

UDF
User-defined function.

UDT
User-defined type.

unambiguous cursor
A cursor that has been defined in a manner that allows a relational database to determine whether blocking can be used with the answer set. A cursor defined FOR FETCH ONLY or FOR READ ONLY can be used with blocking, whereas a cursor defined FOR UPDATE cannot.

unbind session (UNBIND)
A request to deactivate a session between two logical units (LUs).

uncommitted read (UR)
An isolation level that allows an application to access uncommitted changes of other transactions. The application does not lock other applications out of the row it is reading, unless the other application attempts to drop or alter the table.

uncoordinated transaction
A transaction that accesses more than one resource but its commit or rollback is not being coordinated by a Transaction Manager.

Unicode**
An international character encoding scheme that is a subset of the ISO 10646 standard. Each character supported is defined using a unique 2-byte code.

unique constraint
The rule that no two values in a primary key or key of a unique index can be the same.

unique index
An index that ensures that no identical key values are stored in a table.

unique key
A key that is constrained so that no two of its values are equal.

unit of work
A recoverable sequence of operations within an application process. At any time, an application process is a single unit of work, but the life of an application process can involve many units of work as a result of commit or rollback operations. Synonym for transaction.

unit-of-work table
A replication control table at the source server that contains commit records read from the database log or journal. The records include a unit-of-recovery ID that can be used to join the unit-of-work table and the change data table to produce transaction-consistent change data. For DB2, the unit-of-work table optionally includes the correlation ID, which can be useful for auditing purposes.

untyped parameter marker
A parameter marker that is specified without its target data type. It has the form of a single question mark.

update rule
A condition enforced by the database manager that must be met before a column can be updated.

UR
Uncommitted read.

user copy table
A target table whose content matches all or part of a source table and contains only user data columns.

user-defined distinct type
See distinct type.

user-defined function (UDF)
A function that is defined to the database management system and can be referenced thereafter in SQL queries. It can be one of the following functions:

user-defined performance variable
A performance variable created by a user and added to the performance variable profile.

user-defined target table
Any type of target table that is created by a user for an application and can be used in the replication process.

user-defined type (UDT)
A data type that is not native to the database manager and was created by a user. See also distinct type.

user mapping
An association between the authorization under which a user connects to a federated server and the authorization under which the user connects to a data source.

user table
A table created for and used by an application before it is defined as a replication source. It is used as the source for updates to read-only target tables, consistent change data tables, and replicas.

UTC
Coordinated Universal Time.



V

value
(1) Smallest unit of data manipulated in SQL.
(2) A specific data item at the intersection of a column and a row.

variable
A data element that specifies a value that can be changed.

variant function
A user-defined function whose result is dependent on its input parameter values as well as other factors. Successive invocations with the same parameter values might produce different results. Contrast with not-variant function.

varying-length string
A character, graphic, or binary string whose length is not fixed but can range within set limits.

view
A logical table that consists of data that is generated by a query.

Visual Explain
A tool that lets database administrators and application programmers use a graphical interface to display and analyze detailed information on the access plan of a given SQL statement. The tasks provided by this tool can be accessed from the Control Center.



W

warm start
A restart that allows reuse of previously initialized input and output work queues. Contrast with cold start.

warm start table
A table used by the Capture program to save position in a DBMS log for later reference during warm start.

well known address
An address used to uniquely identify a particular node in the network to establish connections between nodes. The well known address is a combination of the network address and the port used on the logical node.

wrapper
A mechanism utilizing routines and control information that the federated server uses to communicate with, and retrieve data from, a data source.

wrapper module
A library containing the routines and control information that make up a wrapper.



X

XID
Exchange station ID.