Glossary - Database Design and Development: An Essential Guide for IT Professionals - page 712

Hashing algorithm. A software routine that converts the primary key value to a
storage address to store that particular record.
Hierarchical data model. A data model where the data structures are arranged in
a top-down manner as in an inverted tree.
Homonyms. Two or more data elements having the same name but containing dif-
ferent data.
Horizontal partitioning. In a relational data model, the division of a relation hori-
zontally as a sets of rows.
Identifier. One or more attributes whose values can uniquely identify the instances
of an object set or entity type.
Identifying relationship. A relationship between two entity types where one entity
type depends on another entity type for its existence. For example, the entity type
ORDER DETAIL cannot exist without the entity type ORDER.
Index. A table or data structure containing sorted values of one or more columns
in a given relation and the storage addresses of the rows. An index speeds up
data access.
Inheritance. The property of subsets inheriting the attributes and relationships of
their superset.
Internal schema. Definition of the internal structure of a database.
I/O (input/output). Abbreviation used for indicating a database read/write opera-
tion. Excessive I/Os degrade system performance.
ISAM (indexed-sequential access method). A data access method using indexes in
file-oriented data systems.
IT (information technology). Covers all computing and data communications
in an organization. Typically, the CIO is responsible for IT operations in an
organization.
JAD (joint application development). A methodology for developing computer
applications in which IT professionals and end-users cooperate and participate
in the development effort.
Key. One or more attributes whose values can uniquely identify the rows of a rela-
tional table.
Local information. Information in a distributed database that is of interest to users
in the local location.
Local transaction. A transaction in a distributed database system requiring data
only from the local location for completion.
Lock. Mechanism to prevent access of a portion of the database by other transac-
tions. Locks may be applied at different levels of database structures. Also, there
are different types of locks such as shared or exclusive locks.
Log. A file used by the DBMS to record all database transactions. The log file is
used for recovery of the database in case of failures. The log file is also known
as the journal file.
Logical data model. Also referred as a conventional data model, consists of the
logical data structure representing the information requirements of an organiza-
tion. This data model conforms to the conventions of a class of database systems
such as hierarchical, network, relational, and so on.