ER Model Basics (Contd.)

• Relationship sets can also have descriptive attributes

  • the since attribute of Works_In

• Translating a relationship set to a relation -- attributes of relation must include:

  • Keys for each participating entity set (as foreign keys).
    • This set of attributes forms superkey for the relation.
  • All descriptive attributes.

CREATE TABLE Works_In(

ssn CHAR(1),

did INTEGER,

since DATE,

PRIMARY KEY (ssn, did),

FOREIGN KEY (ssn)

REFERENCES Employees,

FOREIGN KEY (did)

REFERENCES Departments)

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