ITPEC IP October 2020 Question 28

Through the values of corresponding fields — the relational model links records by matching data values, not by position or pointers.

A record in one table is associated with a record in another when a field holds the same value in both: the product code in a sales row matches the product code, the primary key, of one row in the Products table. The field in the referring table is a foreign key. A join uses this match to combine the rows; how the rows are physically stored plays no part.

Answer (b)

Why not others:

• •(a) — the rows of a relational table have no defined order, so a row's position means nothing; the first row of one table has no link to the first row of another
• •(c) — pointers linking parent and child records belong to the hierarchical (and network) database model, not the relational model
• •(d) — a hash function computes a storage location from a key so that one record can be found quickly; it is an access method, not a way to relate records to each other

Key rule: In a relational database every relationship is expressed by data values (a foreign key matching a primary key), which keeps the logical design independent of how the data is stored.

Databases · AI-written, may contain errors