Question

Which one of the options given below refers to the degree (or arity) of a relation in relational database systems?

• A. Number of attributes of its relation schema.
• B. Number of tuples stored in the relation.
• C. Number of entries in the relation.
• D. Number of distinct domains of its relation schema.

Hint:

Remember: In DBMS — Degree = Number of attributes (columns), Cardinality = Number of tuples (rows). This distinction often appears in exams.

Answer 1

The Correct Option is A

Step 1: Recall the concept of degree (arity).
In relational database systems, the degree (or arity) of a relation is defined as the number of attributes (columns) in the relation schema.
Step 2: Clarify the difference with cardinality.
- The cardinality of a relation refers to the number of tuples (rows) it contains.
- The degree is independent of the number of tuples; it only depends on how many attributes are defined in the schema.
Step 3: Eliminate wrong options.
- (B) refers to the number of tuples $\Rightarrow$ cardinality, not degree. ✘
- (C) “number of entries” is vague and not a standard DBMS term. ✘
- (D) “number of distinct domains” is unrelated to degree; domains define allowable values. ✘
Hence, option (A) is correct. \[ \boxed{\text{Degree (arity) of a relation = Number of attributes in its schema.}} \]