Database Management with Web Site Development Applications
Key Terms Chapter 3
by Greg Riccardi

Attribute value The values of a specific attribute for one entity
Attributes (properties) The characteristics that describe an entity
Cardinality constraint A restriction on the cardinality of a role of a relationship. Typical constraints are to-one, in which an entity may be related to no more than one entity of the related type, and to-many, in which an entity may be related to an unlimited number of entities of the related class. A cardinality constraint may specify a minimum or maximum number of related entities
Cardinality ratio constraint A combination of two cardinality constraints, one on each role of a relationship. The three basic types of cardinality ratios are one-to-one, one-to-many, and many-to-many
Composite attribute An attribute whose value is composed of a collection of individual fields
Conceptual data model or conceptual schema A precise definition of the data requirements of a system that is understandable to both users and developers of a database. This model includes detailed descriptions of data types, relationships, and constraints and is often represented as an E-R model, E-R diagram, or object-oriented model
Constraint A limitation on the contents of a database. Data models include constraints on the values of attributes and the cardinality of relationships, among others
Domain The combination of type and constraint that defines the set of possible values of an attribute. Each attribute value must be a member of the domain of the attribute
Entity (instance) An object in the real world that is of interest to the information system
Entity class The common characteristics that represent a collection of entities
External schema A definition of a userís or applicationís view of the information content of a system
Key A set of attributes of an entity class whose values uniquely identify an entity
Key constraint A constraint on the entities of a class that no two different entities can have the same values for a specific set of attributes. This set of attributes is a key of the class
Logical data model or logical schema The definition of the information content of a system in a manner that can be used to create a database
Mandatory participation constraint A cardinality constraint on a role in a relationship that requires an entity to be related to at least one entity of the related class
Multi-valued attribute An attribute whose value is a set of values
Null value A special attribute value that is different from any value in the domain of the attribute. The meaning of a null attribute value of an entity is ambiguous. It may represent a missing value, one that is unknown, or an attribute that is not applicable to the entity
Optional participation constraint A cardinality constraint on a role in a relationship that allows an entity to be related to no entity of the related class
Physical data model or physical schema The definition of the information content of a system in physical terms
Primary key One of the keys of an entity class that is chosen to identify the entities
Relationship (instance) An association between two or more entities
Relationship type A representation of the possibility that entities of two or more entity classes may be associated
Role The function of an entity in a relationship
Schema A precise description of one or more aspects of a database system
Single-valued attribute An attribute with a single, indivisible value