What is a bridging table and when is it used?

• A. A bridging table is used to store a list of values that cannot be related.
• B. A bridging table is used to store a single entity's attributes.
• C. A bridging table is used to store derived attributes.
• D. A bridging (junction) table resolves many-to-many relationships and stores any relationship attributes.

Answer: (D)

The main idea is how to model many-to-many relationships with a bridging (junction) table. When two entities can relate to many of each other, you can’t capture all those connections with a single foreign key in either table. Instead, you create a separate bridging table that contains the primary keys of both entities as foreign keys. Each row represents one specific pairing, and you can also store attributes of that particular relationship in the bridge, such as a status, date, or other details relevant to that pairing.

For example, think of students and courses: a bridging table called Enrollments would hold student_id and course_id, and might include a grade or enrollment date. This table links each student to each course they take, and the extra fields describe the enrollment itself, not the student or the course alone.

Other options miss the purpose: a table storing a list of values that cannot be related isn’t about linking entities, a table storing a single entity’s attributes is just a normal entity table, and a table for derived attributes is about calculated data, not the explicit relationships between two entities.