Database Chapter 4

Relational database

A collection of normalized relations with distinct relation names

Attribute

A named column of a relation

Tuple

A row of a relation

Relational database schema

A set of relation schemas, each with a distinct name

Superkey

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

Relation

File

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

Relation

Physically represented as a table (with columns and rows), based on the mathematical concept of a relation

Tuples

Records

Normalized Relation

Relations that have no repeating groups

Primary key

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

View

The dynamic result of one or more relational operations operating on the base relations to produce another relation. Note: It is a virtual relation that does not necessarily exist in the database but can be produced upon request by a particular user, at the time of request.

Cartesian product

The set of all ordered pairs such that the first element is a member of D1 and the second element is a member of D2

Domain

The set of allowable values for one or more attributes

Intension

The structure of a relation, together with a specification of the domains and any other restrictions on possible values

Extension (or State of a Relation)

This is what tuples are called, which changes over time

Composite key

A key that consists of more than one attribute

Base relation

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

Relational schema

A named relation defined by a set of attributes and domain name pairs

Virtual/derived relation

A relation that does not necessarily exist in its own right, but may be dynamically derived from one or more base relations. ---> view

Candidate key

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

General constraints

Additional rules specified by the users or database administrators or a database that define or constrain some aspect of the enterprise

Foreign key

An attribute or set of attributes within one relation that matches the candidate key of some (possibly the same) relation

Relational keys

Attributes that uniquely identifies each tuple in a relation

Integrity rules

Constraints or restrictions that apply to all instances of the database

Domain constraints

Constraints that form restrictions on the set of values allowed for the attributes of relations

Each __________ has a name and is made up of named _____________ (columns) of data each ________ (row) contains one value per attribute

Each *relation* has a name and is made up of named *attributes* (columns) of data each *tuple* (row) contains one value per attribute

Fields

Fields

The degree of an unary relation/one-tuple, binary, ternary, n-ary?

Has one attribute; two attributes; three attributes; any number of attributes

Entity integrity

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

Null

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

Degree

The number of attributes it contains

Cardinality

The number of tuples it contains