D | Understanding DB2: Learning Visually with Examples (2nd Edition)

daemon: A system process that provides a specific service to applications or users.

DAS: See [Database Administration Server]

Data Control Language (DCL): A language used to control access to the DB2 database manager for an instance. Statements such as GRANT, REVOKE, and CONNECT are DCL statements.

Data Definition Language (DDL): A language for describing data and its relationships in a database.

Data Manipulation Language (DML): A subset of SQL statements that manipulates data. Most applications primarily use DML SQL statements, which are supported by the DB2 Connect program. SELECT, INSERT, UPDATE, and DELETE statements are similar across the IBM relational database products.

data mart: A subset of a data warehouse containing data that is tailored and optimized for the specific reporting needs of a department or team. A data mart can be a subset of a warehouse for an entire organization, such as data that is contained in online analytical processing (OLAP) tools.

data mining: The process of collecting critical business information from a data warehouse; correlating the information; and uncovering associations, patterns, and trends.

data source: In a federated system, typically a relational DBMS instance and one or more databases supported by that instance. However, there are other types of data sources that you can include in your federated system, such as flat-file databases and table-structured files.

data type: In SQL, an attribute of columns, literals, host variables, special registers, and the results of functions and expressions.

data warehouse

(1) A subject-oriented nonvolatile collection of data that supports strategic decision making. The warehouse is the central point of data integration for business intelligence. It is the source of data for data marts within an enterprise and delivers a common view of enterprise data.

(2) A central repository for all or significant parts of the data that an organization's business systems collect.

Data Warehouse Center: The component of DB2 UDB that provides both the graphical interface and the software behind it that enables you to work with the components of the warehouse. You can use the Data Warehouse Center to define and manage the warehouse data and the processes that create the data in the warehouse.

Database Administration Server (DAS): A service or a process that assists the Control Center and Configuration Assistant when working on administration tasks.

database administrator (DBA): A person responsible for the design, development, operation, security, maintenance, and use of a database.

database agent: A representation for the physical process or thread that will do the actual work inside the database engine.

database client: A workstation that accesses a database on a database server.

database configuration file: A file created when a database is created; it resides where that database resides. There is one configuration file per database. Its parameters specify, among other things, the amount of resources to be allocated to that database. You can change the values for many of the parameters to improve performance or increase capacity. Different changes may be required, depending on the type of activity in a specific database.

database configuration parameter: A parameter whose value limits the system resources that a database can use.

database connection services (DCS) directory: A directory that contains entries for remote host 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 that provides the base functions and configuration files needed to use the database.

database function: The relationship between a set of input data and a set of result values.

database log: A set of primary and secondary log files consisting of log records that record all changes to a database. The database log rolls back changes for units of work that are not committed and recovers a database to a consistent state.

database-managed space (DMS) table space: A table space whose space is managed by the database.

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 Configuration parameter: A configuration parameter that is established when the instance is created. Most Database Manager Configuration parameters affect the amount of system resources that will be allocated to a single instance of the database manager, or they configure the setup of the database manager and the different communications subsystems based on environmental considerations.

database manager instance

(1) A logical database manager environment similar to an image of the actual database manager environment. It is possible have several instances of the database manager product on the same workstation. Use these instances to separate the development environment from the production environment, tune the database manager to a particular environment, and protect sensitive information.

(2) The DB2 code that manages data. An instance has its own databases (which other instances cannot access), and all its database partitions share the same system directories. It also has separate security from other instances on the same computer.

database name: The identifying name that a user provides as part of the create database command or application programming interface. A database name must be unique within the location in which it is cataloged.

database node: See [database partition]

database object

(1) An association within a database to anything that can be monitored.

(2) Anything that SQL can create or manipulate. Tables, views, indexes, packages, triggers, and table spaces are database objects.

database partition: In a partitioned database environment, a part of the database that consists of its own user data, indexes, configuration files, and transaction logs.

database partition group: In a partitioned database environment, a named set of one or more database partitions. This term replaces the term nodegroup.

database partition server: In a partitioned database environment, an occurrence of DB2 that is recorded in the db2nodes.cfg file.

Database Partitioning Feature (DPF): The feature of DB2 UDB Enterprise Server Edition to work with a partitioned instance.

database request module (DBRM): A data set member created by the DB2 for z/OS and OS/390 precompiler and that contains information about SQL statements. DBRMs are used in the bind process.

database server: The target of a request from a local application or an intermediate database server. In the DB2 environment, the distributed data facility provides the database server function to access DB2 data from local applications or a remote database server that is acting as an intermediate database server.

database system monitor: A collection of APIs that collect information regarding the state of the database system at the instance, database, and application levels. This information is stored in data elements, which can be examined by taking point-in-time snapshots or by using the Event Monitor to log system activity over a period of time.

DATALINK: An SQL data type that enables logical references from the database to a file stored outside the database.

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

DB2 Application Development Client (DB2 AD Client): A collection of tools that help developers create database applications.

DB2 client: Allows access to a remote database without knowing its physical location. The DB2 client determines the location of the database, manages the transmission of requests to the database server, and returns the results.

DB2 command: An instruction to the operating system to access and maintain the database manager. For example, DB2 commands allow a user to start or stop a database and to display information on current users and the status of databases.

DB2 Connect: A product that enables client applications to read and update data stored on host and iSeries servers.

DB2 control server: A DB2 UDB system that contains the satellite control database, SATCTLDB.

DB2 Data Links Manager: A DB2 feature you can order separately that enables your applications to manipulate data residing in both unstructured files and in the relational database management system (RDBMS). The DB2 Data Links Manager enables DB2 UDB to manage unstructured files as though they were stored directly in the database, and it provides the integration between the RDBMS and the external file systems through extensions to DB2 UDB.

DB2DC: See [Development Center]

DB2 extender: A program you can use to store and retrieve data types beyond the traditional numeric and character data, such as image, audio, and video data and complex documents.

DB2 Net Search Extender: A program that provides full-text retrieval through a DB2 stored procedure. The Net Search Extender is primarily optimized for performance, and it can be particularly advantageous in applications where search performance on large indexes and scalability according to concurrent queries are important factors.

db2setup utility: A utility that guides users through the installation process with a graphical interface and online help. You can use this utility to create or assign groups and user IDs, create a DB2 instance, and install product messages. Default values are provided for all required installation parameters.

DB2 Spatial Extender: A program that creates a geographic information system.

DB2 Text Extender: A full text retrieval system integrated in DB2 UDB that provides powerful search features enhanced by additional rich linguistic functionality for applications with highly structured documents. This is particularly useful when the information need is complex, and the quality and precision of the search result are key issues over and above system response times.

DB2 tools catalog: A set of tables or files maintained by the database tools (Data Warehouse Center, Control Center, Task Center, Information Catalog Center) that contains information about the processes and tasks that DB2 runs, such as loads, reorgs, database maintenance processes, data movement processes, and the associated schedules, logs, and dependencies.

DB2 tools metadata: The information about the processes and tasks that DB2 runs, such as loads, reorgs, database maintenance processes, data movement processes, and the associated schedules, logs, and dependencies. The DB2 tools metadata is contained in the DB2 tools catalog.

DB2 XML Extender: A program that is used to store and manage XML documents in DB2 tables. Well-formed and validated XML documents can be generated from existing relational data, stored as column data, and the content of XML elements and attributes can be stored in DB2 tables.

DBA: See [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 DB2 Control Center.

DBCLOB: See [double-byte character large object]

DBCS: See [double-byte character set]

DBMS: See [database management system]

DBRM: See [database request module]

DDF: See [distributed data facility]

DDL: See [Data Definition Language]

deadlock: A condition under which a transaction cannot proceed because it is dependent on exclusive resources that are locked by another transaction, which in turn is dependent on exclusive resources that are 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 exists. When it detects a deadlock condition, the detector stops one of the transactions involved in the deadlock. This transaction is rolled back and the other transaction can proceed.

Decision Support System (DSS): In the Information Catalog Center, a system of applications that help users make decisions. This kind of system lets users work with information that is presented in meaningful ways; for example, spreadsheets, charts, and reports.

declared temporary table: A table that holds temporary data and is defined with the SQL statement DECLARE GLOBAL TEMPORARY TABLE. Information about declared temporary tables is not stored in the DB2 catalog, so this kind of table is not persistent and can be only used by the application process that issued the DECLARE statement.

degree of parallelism: The number of concurrently executed operations that are initiated to process a query.

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 ASCII (DEL): A file format that contains a stream of ASCII characters separated by row and column delimiters.

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.

delta backup: A copy of all database data that has changed since the last successful backup (full, incremental, or delta) of the table space in question. A delta backup is also known as a differential or noncumulativebackup image . The predecessor of a delta backup image is the most recent successful backup that contains a copy of each of the table spaces in the delta backup image.

denormalization: The intentional duplication of columns in multiple tables whose consequence is increased data redundancy. Denormalization is sometimes necessary to minimize performance problems and is a key step in designing a physical relational database design.

dependent: In SQL, an object (row, table, or table space) that has at least one parent.

dependent foreign key table: A table of a given table that has at least one foreign key constraint referencing the given table.

dependent immediate materialized query table: A dependent materialized query table that is defined with the REFRESH IMMEDIATE option.

dependent materialized query table: A materialized query table that references a given table directly or indirectly (for example, from a view) in its materialized query table definition.

dependent row: A row containing a foreign key that matches the value of a parent key in the parent row. The foreign key value 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.

dependent table space: A table space that contains a dependent of a parent table.

Development Center: A DB2 component that provides a graphical interface for building, testing, and deploying stored procedures and user-defined functions. Features include a server view, an integrated SQL debugger, export and import wizards, and an editor.

differential backup image: See [delta backup]

dimension: A data category, such as time, accounts, products, or markets. The elements of a dimension are referred to as members. Dimensions offer a very concise, simple way of organizing and selecting data for retrieval, exploration, and analysis. Dimensions also represent the highest consolidation level in a multidimensional database outline.

dimension block index: In multidimensional clustering, a block index that is automatically created for a particular dimension when the dimension is defined in an MDC table. This index maintains the clustering of data along that dimension, together with the other dimensions defined in the table.

dimension table: The representation of a dimension in a star schema. Each row in a dimension table represents all of the attributes for a particular member of the dimension.

disaster recovery: The activities that are required to restore the database in the event of a fire, earthquake, vandalism, or other catastrophic events. Typically, disaster recovery requires that you restore the entire database, so if a major disaster occurs, a full database backup is available from a standby site.

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 data facility (DDF): A facility that provides the application server function for accessing DB2 data from remote applications on DB2 for z/OS.

Distributed Relational Database Architecture (DRDA): The 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.

DML: See [Data Manipulation Language]

DMS table space: See database-managed space table space.

DNS: See [Domain Name Server]

domain: A part of a network that is administered as a unit with a common protocol.

domain name: The name by which TCP/IP applications refer to a TCP/IP host within a TCP/IP network. A domain name consists of a sequence of names separated by dots. For example: www.ibm.com.

Domain Name Server (DNS): A TCP/IP network server that manages a distributed directory that maps TCP/IP host names to IP addresses.

double-byte character large object (DBCLOB): A data type consisting of a sequence of double-byte characters, with a size ranging from 0 bytes to 2GB minus 1 byte, that can be used to store large double-byte text objects. This kind of 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. These character sets are commonly used by national languages, such as Japanese and Chinese, that have more symbols than can be represented by a single byte.

double-precision floating point number: In SQL, a 64-bit approximate representation of a real number.

DPF: See [Database Partitioning Feature]

DRDA: See [Distributed Relational Database Architecture]

DSS: See [Decision Support System]

dual log path: A secondary log path that maintains duplicate copies of online archived files and the active log.

DUOW: See [distributed unit of work]

dynamic SQL: SQL statements that are prepared and executed at runtime. In dynamic SQL, the SQL statement is contained as a character string in a host variable and is not precompiled.