How do you map an identifying relationship in an ERD to a relational schema?

• A. The child table includes no reference to the parent table.
• B. The child table's primary key is independent of the parent keys.
• C. The child table includes the parent table's primary key as part of its composite primary key or as a foreign key with part of a composite primary key.
• D. The parent table's primary key becomes a foreign key in the child with no key involvement.

Answer: (C)

In an identifying relationship, the child’s identity depends on the parent, so the parent’s key must be part of the child’s key in the relational schema. That means the child table should either use the parent’s primary key as part of a composite primary key or store the parent’s primary key as a foreign key that is itself part of a composite primary key. This ensures each child row is uniquely identified within the context of its parent and guarantees that a child cannot exist without a corresponding parent.

For example, if the parent has a primary key ParentID, the child could have a primary key like (ParentID, ChildID) or (ChildID, ParentID), with ParentID also serving as a foreign key to the parent. This reflects the identifying relationship. Other options fail because they treat the child as independent of the parent or only use a plain foreign key without integrating the parent key into the child’s primary key.