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DBMS BCA Unit-2 ER Model - Introduction Components of an E-R Model Entity Entity Identifier: Key Attributes Strong and Weak Entity Sets Attributes and Domain Types of Attributes Relationships E-R DIAGRAM ERD for STUDENT Entity ERD for CAR Entity Entity Types for a COMPANY Database Relationship Types of COMPANY Database THE RELATIONAL MODEL Structure of Relational Databases Super Keys and Candidate Keys Relational Constraints Database Operations and Constraint Violations


Entity Identifier: Key Attributes

An entity type usually has an attribute whose values are distinct for each individual entity in the collection. Such an attribute is called a key attribute and its values can be used to identify each entity uniquely.