active log -The portion of the DB2 log to which log records are written as they are generated. The active log always contains the most recent log records, whereas the archive log contains those records that are older and will no longer fit on the active log.

application plan -A control structure used by DB2 to process SQL statements during the execution of an application. The application plan is created during the BIND process.

archive log -The portion of the DB2 log that contains log records that have been moved (off-loaded) from the active log because there is no more space for them in the active log.

bind -The process of creating an application plan. The bind process determines which access paths to the data the application plan will utilize. Binds can be done automatically and dynamically.

BSDS (bootstrap data set) -A VSAM KSDS dataset that contains name and status information for DB2, as well as RBA range specifications for all active and archive log datasets. It also contains passwords for the DB2 Directory and Catalog, and lists of conditional restart and checkpoint records.

buffer pool -The main storage reserved to satisfy the buffering requirements for one or more table spaces or indexes.

clustering index -The index that determines how rows are physically ordered in a tablespace.

commit -An operation that terminates a unit of recovery. A commit releases all locks. Data that was changed is now consistent.

commit point -A point in time when data is considered consistent. See "point-of consistency".

database -A collection of tables, or a collection of table spaces and index spaces.

DB2 Catalog -DB2-maintained tables that contain descriptions of DB2 objects such as tables, views, and indexes.

DB2 Directory -The system database that contains internal objects such as databasedescriptors, skeleton cursor tables, and opening/closing log relative byte addresses (RBA) for tablespaces.

DB2 command -An instruction to the DB2 subsystem allowing a user to start or stop DB2, to display information on current users, to start or stop databases, to display information on the status of databases, and so on.

DB2 Interactive (DB2I) -The DB2 facility that provides for the execution of SQL statements, DB2 (operator) commands, programmer commands, and utility invocation.

DB2 utility -A standard MVS batch job which requires that DB2 be running. Example DB2 utilities are COPY, LOAD, QUIESCE, and REORG.

dynamic SQL -SQL statements are created, prepared, and executed while a program is executing. It is, therefore, possible with dynamic SQL to change the SQL statement during program execution and have many variations of a SQL statement at run time.

embedded SQL -Also known as static SQL, these are SQL statements that are created and prepared before program execution. After the SQL statement is embedded in an application, the only variance allowed at execution is the values of the host variables.

foreign key -A column, or combination of columns, whose values must match those of a primary key in the same or different table. A given foreign key value represents a reference from the row(s) containing it to the row containing the matching primary key value. The problem of ensuring that every foreign key value does in fact match a value of the corresponding primary key is known as the referential integrity problem.

image copy -An exact reproduction of all or part of a table space. The DB2 COPY utility can make full image copies (to copy the entire table space) or incremental image copies (to copy only those pages modified since the last image copy).

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

index space -A page set used to store the entries of one index.

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

leaf page -The lowest-level index page which contains the keys and RIDs that identify individual rows in the related table.

log -A collection of records that describe the events that occur during DB2 execution and their sequence. The information thus recorded is used for recovery in the event of a failure during DB2 execution. Each log record is identifiable by the RBA of the first byte of its header, which is called the 'relative byte address of the record'. The record RBA is like a timestamp in that it uniquely identifies a record that starts at a particular point in the continuing log.

log RBA -Each byte in the DB2 log is addressable by its offset from the beginning of the log, and that offset is known as its relative byte address.

nonleaf page -An intermediate page in the index hierarchy between the root page and the leaf pages. Each entry in the nonleaf page points to a subordinate nonleaf or leaf page.

null -A special value that indicates the absence of information or that the information is unknown.

object -Anything that can be created or manipulated with SQL -- that is, databases, table spaces, tables, views, or indexes.

page -A unit of storage within a table space (4K or 32K) or index space (4K). In a table space, a page contains one or more rows of a table.

point-of-consistency -A point in time at which all data is static and consistent. There are three types of point-of-consistency: 1) applications points-of-consistency guarantee the integrity of the application data at a particular point in time; 2) table space set points-of-consistency are points at which all of the data in a set of table spaces is static and consistent; 3) system points-of-consistency are those points in a DB2 system at which all data -- both system and user -- within that system are static and consistent.

quiesce point -An established point that corresponds to a point of consistency for all identified table spaces in the control statement. The value of the quiesce point is stored in the catalog table SYSIBM.SYSCOPY.

primary key -A column, or combination of columns, within a table whose values together form the "principal unique identifier" of rows in that table. In other words, a table's primary key serves to uniquely identify row in that table.

recovery -The process of rebuilding databases after a system failure.

recovery log -See log.

referential integrity -The condition that exists when all intended references from data in one column of a table to data in another column of the same or a different table are valid.

RID -The internal record identifier used to locate a given row in a table. It is composed of the page number and record id within the page.

SQL (Structured Query Language) -A database language, originally developed by IBM, to support the definition, manipulation, and control of data in a relational database.

SQLCA -SQL communication area. The communication block of variables used by DB2 to inform an application program of the status of the system as a result of a prior SQL call.

SQLDA -SQL descriptor area. The group of variables used in the execution of some SQL statements. It is used in dynamic SQL programs.

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

table space -A page set used to store the records of one or more tables.

table space set -The group of all tables related to each other through referential constraints, which must be recovered to the same point of consistency.

thread -The DB2 structure that defines the existence of a connection between an application and DB2 and controls the access allowed.

view -A virtual table in a database whose contents are defined by a query. A view definition consists of SQL statements, and is stored in the DB2 Catalog. To the user, a view appears to be just another table.