In database design, an entity is classified as strong or weak based on whether it has a primary key that uniquely identifies its records.

Differences Between Strong and Weak Entities:

CREATE TABLE Orders (

OrderID INT PRIMARY KEY,

CustomerID INT

);

CREATE TABLE OrderDetails (

OrderDetailID INT,

OrderID INT,

ProductID INT,

PRIMARY KEY (OrderDetailID, OrderID),

FOREIGN KEY (OrderID) REFERENCES Orders(OrderID)

);

Orders is a strong entity (has OrderID as its own primary key).

OrderDetails is a weak entity (depends on OrderID for uniqueness).

Why Other Options Are Incorrect:

Option A (Association) (Incorrect): Associations describe relationships but do not define strong/weak entities.

Option C (Foreign key) (Incorrect): Weak entities depend on foreign keys, but primary keys define their status.

Option D (Cardinality) (Incorrect): Cardinality defines relationship constraints but does not differentiate entity types.

Thus, the correct answer is Primary key, as it is the defining characteristic between strong and weak entities.