Glossary - Database Design and Development: An Essential Guide for IT Professionals - page 710

DCL (data control language). Language component in a DBMS to control the
security of a database system. DCL is used to grant and revoke database access
privileges to users.
DDBMS (distributed database management system). Software that manages a dis-
tributed database as a logical whole.
DDL (data definition language). Language component in a DBMS used for defin-
ing the data structures to the data dictionary as schema definitions.
DDLC (database development life cycle). A complete process from beginning
to end, with distinct phases for defining information requirements, creating
the data model, designing the database, implementing and maintaining the
database.
Deadlock. A situation in which neither of two transactions can complete because
each is holding exclusively a portion of data in the database that is needed by
the other transaction. DBMSs contain provisions for deadlock detection and
deadlock prevention.
Decomposition of relations. Splitting of relations or tables into smaller relations
for the purpose of normalizing them.
Degree. The number of entity types or object sets that participate in a relationshp.
For a binary relationship the degree is 2.
Denormalization. Introduction of controlled redundancy in a database, usually
done for the purpose of improving data access performance.
Distributed database. A database where data is physically stored in more than one
location.
DKNF (domain-key normal form). This is the ultimate goal in transforming a rela-
tion into the highest normal form. A relation is in DKNF if it represents one
topic and all of its business rules are able to be expressed through domain con-
straints and key relationships.
DML (data manipulation language). Language component in a DBMS to perform
data manipulation operations in the database.
Domain. The set of all permissible data values and data types for an attribute of
an object set.
DSS (decision-support system). Application that enables users to make strategic
decisions. DSSs are driven by specialized databases.
EBCDIC (Extended Binary-Coded Decimal Interchange Code). A coded charac-
ter set of 256 eight-bit characters commonly used in mainframe computer
systems.
Encryption. Encoding of data using key data strings so that the encrypted data
becomes unintelligible to an intruder. Decryption restores the decoded data to
its original form to be used by an authorized user.
Entity. A real-world “thing” of interest to an organization.
Entity instance. A single occurrence of an entity type. For example, a single invoice
is an instance of the entity type called INVOICE.
ERD (entity-relationship diagram). A graphical representation of entities and their
relationships.
Entity set. The collection of all entity instances of a particular type of entity.