A relation has:

• Relational Schema
• Relation instance

Relational Schema:

A relational schema shows the relation's name, its attributes and the domain of every attribute. If R is the name of a relation and A₁, A₂...A_n is a list of attributes showing R then R (A1, A₂...A_n) is known as a relational schema. Every attribute in this relational schema takes a value from some explicit domain called Domain (Ai).

For instance, the relational schema for relation PERSON as in Figure will be: PERSON (PERSON_ID:integer, NAME: string, AGE:integer, ADDRESS:string)

Total number of attributes in a relation indicates the degree of a relation. Hence the

PERSON relation includes four attributes, so this relation is of degree 4

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