15.00 - Definition of Attribute - Teradata Database

Teradata Database Design

prodname
Teradata Database
vrm_release
15.00
category
User Guide
featnum
B035-1094-015K

Definition of Attribute

An attribute is a characteristic of an entity. Every entity has at least one attribute: its primary key (More accurately, a candidate key). Attributes are expressed as nouns qualified by adjectives that clarify their role.

An attribute plays one of three possible roles in any table:

  • Primary key attributes identify the entity or relationship modeled by a table (note the fuzzy boundaries among entities, relationships, and tables, which led Codd to his pointed criticism of the E-R approach).
  • Primary key attributes are said to be identifier attributes because they uniquely identify an instance of an entity.

  • Foreign key attributes define relationships between and among entities or among entities and relationships.
  • A foreign key attribute can be an identifier attribute if it is part of a composite primary key; otherwise, foreign key attributes are descriptor attributes.

  • Nonkey attributes further describe the entity or relationship modeled by a table.
  • Nonkey attributes are said to be descriptor attributes because they specify a nonunique characteristic of an instance of an entity.

    In the relational model, attributes have the same properties as they do in E-R theory.