Discussion
Which one of the options given below refers to the degree (or arity) of a relation in relational database systems?
Answer: A
The degree (arity) is the number of attributes of its relation schema.
A relation schema R(A1, A2, ..., An) has degree n: a binary relation has two attributes, a ternary one three. The degree is fixed by the schema and does not change as rows are inserted or deleted.
The number of tuples stored in the relation is its cardinality, which changes with every insert and delete, and 'number of entries' describes the same thing. The number of distinct domains is not a defined property: several attributes can share one domain (two date columns, say), so it can be smaller than the degree.
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