Binary vs. Ternary Relationships (Contd.)

• The key constraints allow us to combine Purchaser with Policies and Beneficiary with Dependents.

• Participation constraints lead to NOT NULL constraints.

• What if Policies is a weak entity set?

CREATE TABLE Policies (

policyid INTEGER,

cost REAL,

ssn CHAR(11) NOT NULL,

PRIMARY KEY (policyid).

FOREIGN KEY (ssn) REFERENCES Employees,

ON DELETE CASCADE)

CREATE TABLE Dependents (

pname CHAR(20),

age INTEGER,

policyid INTEGER,

PRIMARY KEY (pname, policyid).

FOREIGN KEY (policyid) REFERENCES Policies,

ON DELETE CASCADE)

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