A relational database is a type of database that stores data in tables with rows and columns.
- Each table represents a relation , which is a set of facts about a certain entity or concept.
- Each row in a table represents a tuple , which is an instance or occurrence of the relation.
- Each column in a table represents an attribute , which is a property or characteristic of the relation.
- Each attribute has a domain , which is the set of possible values that it can take.
Commonly used terminologies in relational data model:
- Attribute - Characteristic or parameters for which data are to be stored in a relation. Simply stated, the columns of a relation are the attributes which are also referred to as fields.
- Tuple - Each row of data in a relation (table) is called a tuple. In a table with n columns, a tuple is a relationship between the n related values.
- Domain - It is a set of values from which an attribute can take a value in each row. Usually, a data type is used to specify a domain for an attribute.
- Degree - The number of attributes in a relation is called the Degree of the relation
- Cardinality - The number of tuples in a relation is called the Cardinality of the relation.