Introduction to Data Management

Glossary
15873 Tandem Computers Incorporated Glossary-3
Concurrent access. The ability of two or more processes to gain access to the same data
at the same time.
Constraint. In NonStop SQL, a data check that helps protect the integrity of
information in a table by supporting rules that all the values in particular columns of
the table must satisfy.
Context. In PATHMAKER, the set of all reference objects used in a requester,
including both the objects that are displayed on a screen, and the objects that are not
displayed but are used in interprocess messages to other requesters and servers.
Data control statement. In NonStop SQL, a statement used to control process resources
such as locks and cursors.
Data Definition Language (DDL). See DDL.
Data definition statement. In NonStop SQL, a statement used to define, delete, or modify
the catalog definition of a table, column, index, view, constraint, partition, or
authorization.
Data dictionary. In NonStop SQL, the set of all catalogs on a system or a network of
systems and the corresponding set of file labels. In ENSCRIBE, a database that
contains object definitions compiled by the DDL compiler. The dictionary serves as a
map of your business database.
Data management. The collective control of the acquisition, storage, analysis, and
retrieval of data.
Data manipulation statement. In NonStop SQL, a statement used to select, update, insert,
or delete rows in tables.
Database. A data repository, normally on disk, that operates as a single collection of
information. This repository allows rapid access of data by many users at the same
time. The database is a structured set of information that describes some aspect of the
real world, such as all employees of a business. In NonStop SQL, a database is the
collection of all tables and catalogs in the Tandem system.
Database administrator (DBA). The person who defines or manages the database and
who controls access to it.
Database consistency. The accurate correspondence of the data in your database, as
seen by all users, with the real world that the database is supposed to reflect. When
you design a database, you establish certain criteria for the relationship between items
in the database. One criterion for a banking application, for instance, is that an
account balance must always equal the credits minus the debits for that account.
When the database satisfies the criteria, it is said to be consistent. When an
application changes a database, it transforms the database from one consistent state to
another, but during the transformation the database is generally inconsistent. TMF
enforces database consistency by making certain that either all changes imposed by a
transaction are reflected at once in the database, or that none of them are.