Chapter 2 The Relational Model

Primary Key

A candidate key selected to be the main key of a relation. (p. 66)

Alternate Key

A candidate key which was not chosen to be the primary key, but is still present in a relation. (p. 67)

Surrogate Key

A column with a unique, DBMS-assigned identifier that has been added to a table to be the primary key. (p. 70)

Table

A database structure of rows and columns used to create cells that hold data values. Also known as a relation or file. (p. 63)

AUTO_INCREMENT

A function MySQL uses to automatically assign surrogate key numbers. (p. 70)

SEQUENCE

A function Oracle Database uses to to define automatically increasing sequences of numbers that can be used as surrogate key numbers. (p. 70)

Row

A group of columns in a table. Also known as a tuple or record. (p. 63)

Composite Key

A key of a relation that consists of two or more columns. (p. 66)

Unique Key

A key that identifies a unique row. (p. 66)

Nonunique Key

A key that potentially identifies more than one row. (p. 66)

Column

A logical group of bytes in a row of a relation or a table. Also known as a(n) field or attribute. (p. 63)

Null Value

A missing value in a cell of a relation. (p. 74)

Referential Integrity Constraint

A relationship constraint on foreign key values. Specifies that the value of a foreign key must be a proper subset of the values of the primary key to which it refers. (p. 72)

Relation

A two-dimensional table consisting of rows and columns. Also known as a table or file. (p. 63)

Candidate Key

An attribute or a group of attributes that identifies a unique row in a relation. Can be chosen as the primary key. (p. 66)

Foreign Key

An attribute that is a key of one or more relations other than the one in which it appears. (p. 70)

Field

Another term for column or attribute. (p. 65)

Attribute

Another term for column or field. (p. 65)

Tuple

Another term for row or record. (p. 65)

Record

Another term for row or tuple. (p. 65)

File

Another term for table or relation. (p. 65)

Key

One or more columns of a relation that is used to identify a row. (p. 66)

Identity

Set of specifications that have been set to indicate to SQL Server that a surrogate key column exists. (p. 70)

Is Identity

Sets the value of a key to a surrogate.

Entity

Something of importance to the user that needs to be represented in the database. (p. 63)

Identity Increment

The amount that is added to each key value to create the next key. (p. 70)

Identity Seed

The starting value of a surrogate key. (p. 70)