Database Chapter 4

Composite key

A key that consist of more than one attribute

Attributes

A named column of a relation

Base relation

A named relation corresponding to an entity in the conceptual schema, whose tuples are physically stored in the database

Tuple

A row of a relation

Domain

A set of allowable values for one or more attributes

Candidate key

A super key such that no proper subset is a superkey within the relation

Superkey

An attribute or set of attributes, that uniquely identifies a tuple within a relation

Foreign Key

An attribute, or set of attributes, within one relation that matches the candidate key of some relation

Referential integrity

If a foreign key exists in a relation, either the foreign key value must match a candidate key value of some tuple in its home relation or the foreign key value must be wholly null

Entity Integrity

In a base relation, no attribute of a primary key can be null

Intension

Internal structure of the database

Normalized relations

Relations that have no repeating groups

Null

Represents a value for an attribute that is currently unknown or is not applicable for this tuple

Relational database schema

Set of these with distinct name

Relation

Table with columns and rows

Primary key

The candidate key that is selected to identify tuples uniquely within the relation

Alternate keys

The candidate keys that are not selected to be the primary key

view

The dynamic result of one or more relational operations operating on the base relations to produce another relation

Degree

The number of attributes it contains

Cardinality

The number of tuples it contains

External

The part that can change (view)

Relational Database

a collection of normalized relations with distinct relation names

General constraints

additional rules specified by the users or database admins of a database that define or constrain some aspect of the enterprise

Relation schema

named relation defined by a set of attribute and domain name pairs