When is the concept of a weak entity used in data modeling? Define the terms owner entity type, weak entity type, identifying relationship type, and partial key.
The correct answer and explanation is :
Concept of a Weak Entity in Data Modeling
A weak entity is used in data modeling when an entity does not have enough attributes to uniquely identify itself without relying on another entity. Weak entities depend on a strong (owner) entity and are associated with them through an identifying relationship. The distinguishing characteristic of a weak entity is that it has a partial key, which alone cannot uniquely identify records but, when combined with the primary key of the owner entity, becomes unique.
Key Terms in Weak Entity Modeling
- Owner Entity Type
The owner entity type is a strong entity that provides the primary key to help uniquely identify the weak entity. It has a primary key that the weak entity depends upon. Example: In a university database, a Student entity is an owner entity for the weak entity Enrollment. - Weak Entity Type
A weak entity type is an entity that cannot be uniquely identified using its own attributes alone and must depend on an owner entity’s primary key. It always has an identifying relationship with an owner entity. Example: Enrollment is a weak entity that depends on Student. - Identifying Relationship Type
The identifying relationship is a one-to-many or one-to-one relationship that links a weak entity to its owner entity. It ensures that each weak entity instance can be uniquely identified using the owner’s key. Example: The relationship “Enrolls” between Student (owner) and Enrollment (weak entity). - Partial Key
A partial key is an attribute or set of attributes in a weak entity that helps uniquely identify the entity when combined with the owner entity’s primary key. Example: Course_ID in Enrollment acts as a partial key.
Illustration
Below is a conceptual diagram of a weak entity relationship.
Weak Entity Relationship Diagram
Here is the conceptual diagram illustrating the weak entity relationship. It visually represents the Student (owner entity), Enrollment (weak entity), their identifying relationship, and the partial key involved.