Chapter 8

Identifier

A candidate key that has been selected as the unique, identifying characteristic for an entity type.

Entity type

A collection of entities that share common properties or characteristics.

Entity-relationship data model

A detailed logical representation of the entities, associations, and data elements for an organization or business area.

Conceptual data model

A detailed model that captures the overall structure of organizational data that is independent of any database management system or other implementation considerations.

Supertype

A generic entity type that has a relationship with one or more subtypes.

Entity-relationship diagram

A graphical representation of an E-R model.

Attribute

A named property or characteristic, of an entity that is of interest to the organization.

Unary relationship

A relationship between instances of one entity type; also called recursive relationship.

Binary relationship

A relationship between instances of two entity types. This is the most common type of relationship encountered in data modeling.

Repeating group

A set of two or more multivalued attributes that are logically related.

Ternary relationship

A simultaneous relationship among instance of three entity types.

Entity instance

A single occurrence of an entity type. Also known as an instance.

Subtype

A subgrouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroupings.

Triggering operation (trigger)

An assertion or role that governs the validity of data manipulation operations such as insert, update, and delete; also called a trigger.

Relationship

An association between the instance of one or more entity types that is of interest to the organization.

Candidate key

An attribute (or combination of attributes) that uniquely identifies each instance of an entity type.

Composite attribute

An attribute that has meaningful component parts.

Optional attribute

An attribute that may not have a value for every entity instance.

Multivalued attribute

An attribute that may take on more than one value for each entity instance.

Required attribute

An attribute that must have value for every entity instance.

Derived attribute

An attribute whose value can be computed from related attribute values.

Associative entity

An entity type that associates the instances of one or more entity types and contains attributes that are peculiar to the relationship between those entity instances; also called a gerund.

Business rules

Specifications that preserve the integrity of the logical data model.

Overlap rule

Specifics that an entity instance can simultaneously be a member of two (or more) subtypes.

Partial specialization rule

Specifics that an entity instance of the supertype does not have to belong to any subtype.

Total specialization rule

Specifies that each entity instance of the supertype must be a member of some subtype of the relationship.

Disjoint rule

Specifies that if an entity instance of the supertype is a member of one subtype, it cannot simultaneously be a member of any other subtype.

Degree

The number of entity types that participate in a relationship.

Cardinality

The number of instances of entity B that can (or must) be associated with each instance of entity A.

Domain

The set of all data types and values that an attribute can assume.