Match the following:

Concept

In Chen-style entity–relationship notation, a diamond denotes a relationship set. Cardinality is read from the connectors on the two sides of that relationship.

A plain line denotes “many” on that side, while an arrow denotes “one”. The pair of connector types therefore determines many-to-many, many-to-one, or one-to-one cardinality.

Application

1. Diagram (a) contains only the relationship diamond R, so it corresponds to (ii), Relationship.

2. Diagram (b) has a plain line on each side of R, so it corresponds to (iii), Many-to-many relationship.

3. Diagram (c) has a plain line on the left and an arrow on the right, so it corresponds to (iv), Many-to-one relationship.

4. Diagram (d) has an arrow on each side of R, so it corresponds to (i), One-to-one relationship.

Cross-check

Counting arrow-ended sides gives zero in (b), one in (c), and two in (d), which independently yields many-to-many, many-to-one, and one-to-one respectively; (a) is the unqualified relationship symbol.

Result

The complete correspondence is (a)→(ii), (b)→(iii), (c)→(iv), and (d)→(i), giving the sequence “ii iii iv i”.