A Level Computer Science OCR Practice Exam

What is a primary issue with a many-to-many relationship in ERM?

1. It simplifies database design

2. It may lead to data redundancy

3. It always requires a unique key

4. It prevents cascading updates

The correct answer is: It may lead to data redundancy

A primary issue with a many-to-many relationship in an Entity-Relationship Model (ERM) is that it can lead to data redundancy. This type of relationship allows multiple instances of one entity to relate to multiple instances of another entity. In practical terms, this means that information can be repeated unnecessarily. For instance, consider a scenario involving students and courses. A student can enroll in multiple courses, and each course can have multiple students. If this relationship is directly represented, attributes related to students or courses may need to be duplicated across several records to accommodate this association. This situation not only complicates the data structure but also increases the likelihood of anomalies during data updates, additions, or deletions, resulting in inconsistencies and wasted storage space. Therefore, managing many-to-many relationships effectively often requires using a junction table or associative entity to break the relationship into two one-to-many relationships, which helps mitigate issues such as redundancy and ensures a more organized database structure.