Entity–Relationship (ER) to relational mapping: Do weak entities get mapped into their own relation (table), or do they not get mapped at all?

Introduction / Context:
This item checks your understanding of how weak entities in an Entity–Relationship (ER) model are transformed (mapped) into relational tables. Weak entities are those that do not have a full primary key by themselves and rely on a strong (owner) entity for identification. The question asks whether weak entities do not get mapped into a relation at all.

Given Data / Assumptions:

• A weak entity has a partial key (sometimes called a discriminator).
• A weak entity participates in an identifying relationship with a strong entity.
• Relational mapping aims to produce tables with primary keys and foreign keys that preserve identification and referential integrity.

Concept / Approach:
During ER-to-relational mapping, every entity set—strong or weak—becomes a relation (table). For weak entities, the relation’s primary key is composite: it includes the owner entity’s primary key (as a foreign key) plus the weak entity’s partial key. This preserves the identifying relationship and ensures uniqueness of weak-entity rows relative to their owner.

Step-by-Step Solution:
Create a relation for the strong (owner) entity with its own primary key.Create a relation for the weak entity with all of its attributes.Add the owner’s primary key attributes to the weak entity’s relation as foreign key columns.Form the weak entity’s primary key by combining the owner’s key columns with the weak entity’s partial key.Declare the identifying foreign key constraint to enforce ownership.

Verification / Alternative check:
Try a common example such as Order (owner) and OrderLine (weak). OrderLine clearly becomes its own table; its primary key often includes order_id plus line_number, and order_id is a foreign key to Order. This confirms weak entities indeed map to relations.

Why Other Options Are Wrong:
Depends only on diagram notation: Incorrect because mapping rules are conceptual, not just notation-driven.True for EER only: Incorrect; standard ER mapping already creates a relation for weak entities.

Common Pitfalls:
Students sometimes think weak entities “merge” into the owner’s table. While occasionally a design can be denormalized that way, the canonical mapping creates a separate relation for the weak entity with an identifying foreign key.

Final Answer:
Incorrect