Strong vs. weak entities: Is a strong entity one whose existence depends on another entity type?

Introduction / Context:
Understanding strong and weak entities is essential in ER modeling. The distinction influences keys, referential integrity, and how tables are created and linked in the relational schema.

Given Data / Assumptions:

• A strong entity has its own primary key that uniquely identifies its instances independently.
• A weak entity lacks a sufficient key of its own and relies on a strong (or owner) entity for identification.
• Dependency here refers to existence and identification, not merely to referencing via a foreign key.

Concept / Approach:
The statement describes a weak entity, not a strong one. A weak entity’s instances cannot be uniquely identified without including the key of another entity (often combined with a partial key). A strong entity is self-identifying and does not depend on the existence of another entity to be uniquely identified.

Step-by-Step Solution:
Check if the entity has a standalone candidate key (e.g., Product(product_id)).If yes, it is strong; if identification requires another entity’s key plus a discriminator (e.g., LineItem(order_id, line_no)), it is weak.Map weak entities with composite primary keys containing the owner’s key.Enforce referential integrity to the owner entity to preserve existence dependence.

Verification / Alternative check:
Attempt to assign a unique identifier without referencing another entity. If impossible, the entity is weak; otherwise, it is strong.

Why Other Options Are Wrong:
“Depends only on foreign key presence” is wrong; many strong entities carry foreign keys without being weak. The database model (relational vs. hierarchical) does not change the definitions.

Common Pitfalls:
Mislabeling intersection entities or line items as strong when they are weak; confusing existence dependence with optional relationships.

Final Answer:
Incorrect