Databases Reference
In-Depth Information
counting:
The process of recording counts of the number of rows in tables that meet
certain criteria as important statistics used in index design, and estimating database
volume and potential materialized view volume, for example. Counting can be done
by using common SQL operators such as COUNT and DISTINCT.
covering index:
An index that covers certain queries, that is, an index with enough
information to answer the query by merely accessing the index and not the target
table.
DAS:
Direct attached storage, the preferred storage medium for small networks and
small databases, where all storage (e.g., internal hard disks, tape drives) is controlled
by the server.
DASD:
Direct access storage device, a general term for a magnetic disk used in a per-
sonal or business computer system.
database:
A collection of interrelated stored data that serves the needs of multiple users;
a collection of tables in the relational model.
database administrator (DBA):
A person in a software organization that is in charge of
designing, creating, and maintaining the databases of an enterprise. The DBA makes
use of a variety of software tools provided by a DBMS.
database life cycle:
An enumeration and definition of the basic steps in the require-
ments analysis, logical design, physical design, creation, and maintenance of a data-
base as it evolves over time.
database management system (DBMS):
A generalized software system for storing and
manipulating databases, for example, Oracle, IBM's DB2, or Microsoft SQL Server
or Access.
data clustering:
The process of storing data (records) near each other on disk because
they have the same or similar key values, to obtain maximum query efficiency. Clus-
tering applies to indexes as well, to coordinate the fast access to clustered data on
disk.
data item:
The basic component of a data record in a file or database table; the smallest
unit of information that has meaning in the real world, for example, customer last
name, address, and identification number.
data mart:
A special-purpose, typically smaller data warehouse; sometimes derived from
an existing data warehouse.
data mining:
A way of extracting knowledge from a database by searching for correla-
tions in the data and to present promising hypotheses to the user for analysis and
consideration.
