Relational model


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Relational model

Relational model is a simple model in which database is represented as a collection of “Relations”, where each relation is represented by a two dimensional table.

Relation Each table is called a relation.

Tuple Each row in a table represents a record and is called a tuple.

Attribute The name of each column in a table is used to interpret its meaning and is called an attribute.

Domain  A domain is a set of permissible values that can be given to an attribute. So every attribute in a table has a specific domain. Values to these attributes cannot be assigned outside their domains.

 

Super Key – A super key is an attribute or set of attributes used to identify the records uniquely in a relation.

Candidate Key –  Candidate keys are minimal super key, i.e. such a key contains no extraneous attribute.

Properties of a candidate key

  • A candidate key must be unique and irreducible
  • A candidate may involve one or more than one attributes. A candidate key that involves more than one attribute is said to be composite.

Primary Key – The primary key is the candidate key that is chosen by the database designer as the principal means of identifying entities within an entity set. The remaining candidate keys, if any, are called alternate keys.