Database Modeling and Design

236 Glossary
dependency of X->>Y. For example, if two rows have the attribute
values ABC and ADE, where X=A and Y has the values C and E,
then the rows ABE and ADC must also exist for an MVD to occur.
A trivial MVD occurs when Y is a subset of X or X union Y is the
entire set of attributes in the table.
normalization—The process of breaking up a table into smaller tables
to eliminate problems with unwanted loss of data (the egregious
side effects of losing data integrity) from the deletion of records
and inefficiencies associated with multiple data updates.
online analytical processing (OLAP)—A query service that overlays
a data warehouse by creating and maintaining a set of summary
views (automatic summary tables, or ASTs) to enable quick access
to summary data.
optional existence—A connectivity between two entities that has a
lower bound of zero. For example, for the “occupies” relationship
between an employee and an office, there may exist some offices
that are not currently occupied.
package—In UML, a package is a graphical mechanism used to organize
classes into groups for better readability.
physical design—The step in the database life cycle involved with the
physical structure of the data; that is, how it will be stored,
retrieved, and updated efficiently. In particular, it is concerned
with issues of table indexing and data clustering on secondary
storage devises (disk).
primary key—A key that is selected from among the candidate keys
for a SQL table to be used to create an index for that table.
qualified association—In UML, an association between classes may
have constraints specified in the class diagram.
record—A group of data items treated as a unit by an application; a row
in a database table.
referential integrity—A constraint in a SQL database that requires,
for every foreign key instance that exists in a table, that the row
(and thus the primary key instance) of the parent table associated
with that foreign key instance must also exist in the database.
reflexive association—In UML, a reflexive association relates a class
to itself.
relationship—A real-world association among one or more entities.
For example, “purchased” could be a relationship between customer
and product.