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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


Attributes and Domain

Attributes
  • An attribute is a property used to describe the specific feature of the entity.
  • So to describe an entity entirely, a set of attributes is used.
    eg:- A Student entity may be described by the Student’s name, age, address, course, etc.

Domain
  • The set of possible values that can be attached to the attribute of an entity type is called the domain of the attribute.
  • An attribute cannot contain a value outside this domain.
    eg:- for PERSON entity PERSON_ID has a specific domain, integer values say from 1 to 100.