h field (or column, or attribute), and the type of each field Example: Students(sid: string, name: string, login: string, age: integer, gpa: real) The degree, also called arity, of a relation is the number of fields The cardinality of a relation instance is the number of tuples in it In Figure 3.1, the degree of the relation (the number of columns) is five, and the cardinality of this instance is six A relational database is a collection of relations with distinct relation names The relational database schema is the collection of schemas for the relations in the database