ITPEC FE Subject A April 2026 Question 19

Topic: DatabasesAlso asked in October 2022

Which of the following is an appropriate description of the mapping between a relational model and relational database in implementation?

a)A domain is mapped to a character type or a character string type.b)A relation is mapped to a table.c)Attributes and columns are ordered from left to right.d)Neither tuples nor rows have duplicates.

Explanation

A relation is mapped to a table — the relational model's concepts each have a counterpart in the implemented database.

The mapping: relation → table, tuple → row, attribute → column, domain → data type.

Answer (b)

Why not others:

•(a) — a domain maps to a data type of any kind (numeric, date, character …), not only character types
•(c) — in the model the attributes of a relation form an unordered set; only the implemented table gives its columns a left-to-right order
•(d) — a relation is a set and has no duplicate tuples, but a table can hold duplicate rows unless a primary key or unique constraint forbids them

Key rule: The relational model is mathematical (sets: no order, no duplicates), while SQL tables are an implementation that allows column order and duplicate rows.

Databases · AI-written, may contain errors

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