ER Model Basics

• Entity: Real-world object distinguishable from other objects.

  • An entity is described (in DB) using a set of attributes.

• Entity Set: A collection of similar entities. E.g., all employees.

  • All entities in an entity set have the same set of attributes.
  • Each entity set has a key.
  • Each attribute has a domain.
  • Can map entity set to a relation easily.

CREATE TABLE Employees

(ssn CHAR(11),

name CHAR(20),

lot INTEGER,

PRIMARY KEY (ssn))

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