Database Modeling and Design

Glossary 235
functional dependency (FD)—The property of one or more
attributes (data items) that uniquely determines the value of one
or more other attributes (data items). Given a table R, a set of
attributes B is functionally dependent on another set of attributes
A if, at each instant of time, each A value is associated with only
one B value.
generalization—A special type of abstraction relationship that specifies
that several types of entities with certain common attributes
can be generalized (or abstractly defined) with a higher-level
entity type, a supertype entity; an “is-a” type relationship. For
example, employee is a generalization of engineer, manager, and
administrative assistant, based on the common attribute job-title.
A tool often used to make view integration possible.
global schema—A conceptual data model that shows all the data and
their relationships in the context of an entire database.
key—A generic term for a set of one or more attributes (data items) that,
taken collectively, enables one to identify uniquely an entity or a
record in a SQL table; a superkey.
logical design—The steps in the database life cycle involved with the
design of the conceptual data model (schema), schema integration,
transformation to SQL tables, and table normalization; the
design of a database in terms of how the data is related, but without
regard to how it will be stored.
lossless decomposition—A decomposition of a SQL table into two or
more smaller tables is lossless if and only if the cycle of table
decomposition (normalization) and the recomposition (joining
the tables back through common attributes) can be done without
loss of data integrity.
mandatory existence—A connectivity between two entities that has
a lower bound of one. One example is the “works-in” relationship
between an employee and a department; every department has at
least one employee at any given time. Note: if this is not true,
then the existence is optional.
multiplicity—In UML, the multiplicity of a class is an integer that
indicates how many instances of that class are allowed to exist.
multivalued dependency (MVD)—The property of a pair of rows in
a SQL table such that if the two rows contain duplicate values of
attribute(s) X, then there is also a pair of rows obtained by interchanging
the values of Y in the original pair. This is a multivalued