ITPEC FE Subject A October 2025 Question 18

Topic: DatabasesAlso asked in April 2022

Which of the following is the appropriate explanation of attributes in the relational model?

a)It is possible to define attributes that have no name.b)The domains of definition for attributes within a relation must not overlap.c)The same name can be given to two (2) or more attributes in a relation.d)There is no meaning in the order of attributes within a relation, and the relation remains unchanged even if the order is changed.

Explanation

Attribute order has no meaning — a relation's attributes form a set, so reordering them gives the same relation.

In the relational model a relation is defined over a set of attributes, each a name paired with a domain. A set has no order, so an attribute is identified by its name, never by its position; for the same reason the order of tuples has no meaning either. It follows that:

•every attribute has a name, the only way to refer to it
•names are unique within a relation
•several attributes may share a domain

Answer (d)

Why not others:

•(a) — an attribute without a name could not be referred to, since position carries no meaning
•(b) — domains may overlap: an order date and a delivery date both draw on the domain of dates
•(c) — two attributes with one name could not be told apart, so names must be unique within a relation

Key rule: In the relational model both attributes and tuples are sets: their order carries no meaning, and duplicates are not allowed.

Databases · AI-written, may contain errors

Previous Next

Practice this exam

This question comes from an official ITPEC past paper. ITPEC Practice is an independent study tool and is not affiliated with ITPEC. See the official FE past-paper collection or Report an issue.