The main construct for representing the data in the relational model is a
•A relation consists of a relation schema and relation instance.
Relation Schema : specifies name of relation, plus name of each field( or
column. or attribute, or property) and the domain of each field.
A domain is referred to in a relation schema by the domain name, and has a set
of associated values.
E.g. Students(sid: string, name: string, login: string, age: integer, gpa: real)
#fields = degree / arity
•An Instance of a relation is a set of tuples, also called records or rows, in which each
tuple has the same number of fields as the relation schema.