A Level Computer Science OCR Practice Exam

What is characteristic of an ERM one-to-many relationship?

1. One entity can connect to many entities

2. Each entity connects only to one other entity

3. All entities must have corresponding entities

4. It is not a valid relationship type

The correct answer is: One entity can connect to many entities

In an Entity-Relationship Model (ERM), a one-to-many relationship signifies that one instance of an entity can be associated with multiple instances of another entity. This is a fundamental concept in database design, where, for instance, a single author can write multiple books. In this case, the "author" entity is the one, while the "books" entity represents the many. Understanding this relationship type is essential for structuring databases that accurately reflect real-world scenarios. In contrast, other options do not accurately describe the characteristics of a one-to-many relationship. For example, suggesting that each entity connects only to one other entity misrepresents the foundational concept of the one-to-many dynamic—it implies a one-to-one relationship instead. Additionally, stating that all entities must have corresponding entities does not hold true in all cases, as some entities can exist without connections in the database (particularly in optional relationships). The assertion that it is not a valid relationship type is incorrect, as one-to-many relationships are indeed a valid and frequently used type in database design.