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Which main characteristic is used to differentiate between strong and weak entities in the process of database design?
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.