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Note for Database Management System - DBMS by Ranjit Kumar

  • Database Management System - DBMS
  • Note
  • West Bengal University of technology - WBUT
  • Electronics and Communication Engineering
  • B.Tech
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Entity-Relationship (E/R) Model 1

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Entity-Relationship (E/R) Model ƒ Widely used conceptual level data model • proposed by Peter P Chen in 1970s ƒ Data model to describe the database system at the requirements collection stage • high level description. • easy to understand for the enterprise managers. • rigorous enough to be used for system building. ƒ Concepts available in the model • entities and attributes of entities. • relationships between entities. • diagrammatic notation. 2

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Entities ƒ Entity - a thing (animate or inanimate) of independent physical or conceptual existence and distinguishable. In the University database context, an individual student, faculty member, a class room, a course are entities. ƒ Entity Set or Entity TypeCollection of entities all having the same properties. Student entity set – collection of all student entities. Course entity set – collection of all course entities. 3

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Attributes Each entity is described by a set of attributes/properties. student entity ƒ StudName – name of the student. ƒ RollNumber – the roll number of the student. ƒ Sex – the gender of the student etc. All entities in an Entity set/type have the same set of attributes. Chosen set of attributes – amount of detail in modeling. 4

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