Chapter 6

Data control language (DCL

Commands used to control a database, including those for administering privileges and committing (saving) data.

Data definition language (DDL)

Commands used to define a database, including those for creating, altering, and dropping tables and establishing constraints.

Data manipulation language (DML)

Commands used to maintain and query a database, including those for updating, inserting, modifying, and querying data.

Materialized view

Copies or replicas of data, based on SQL queries created in the same manner as dynamic views. However, it exists as a table and thus care must be taken to keep it synchronized with its associated base tables.

Relational DBMS

A database management system that manages data as a collection of tables in which all data relationships are represented by common values in related tables.

Catalog

A set of schemas, that, when put together, constitute a description of a database.

Scalar aggregate

A single value returned from an SQL query that includes an aggregate function.

Schema

A structure that contains descriptions of objects created by a user, such as base tables, views, and constraints, as part of a database.

Virtual table

A table constructed automatically as needed by a DBMS. These tables are not maintained as real data.

Base table

A table in the relational data model containing the inserted new data. These tables correspond to the relations that are identified in the database's conceptual schema.

Dynamic view

A virtual table that is created dynamically upon request by a user. It is not a temporary table. Rather, its definition is stored in the system catalog, and the contents of the view are materialized as a result of an SQL query that uses the view. It differs from a materialized view, which may be stored on a disk and refreshed at intervals or when used, depending on the RDBMS.

Vector aggregate

Multiple values returned from an SQL query that includes an aggregate function.