entity relationship model handwritten notes

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Entity-Relationship Model
• Introduction
• Basic Concepts
• Constraints
• Keys
• Entity-Relationship (ER) Diagram
• EER (Extended ER Modeling)
• Summary of Symbols in ER Diagram
• Alternative ER Notations
• Design Issues
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, Introduction
• The entity-relationship (E-R) model is a high-level data
model based on the perception of a real world that consists of a
collection of basic objects, called entities and relationships
among these entities.
• An entity is a thing or object in the real world that is
distinguishable from other objects.
• A relationship is an association among several entities.
• Entities are described by a set of attributes.
• The set of all entities of the same type is called an entity set
and the set of all relationships of the same type is called a
relationship set.
• In this model, we use E-R diagrams to express overall logical
structure of the database. 2-2

, Basic Concepts
• The E-R model employs three basic notations: entity sets,
relationship sets, and attributes.
• Entity Sets:
 An entity is a thing or object in the real world that is distinguishable
from all other objects. For example, specific person, company, event,
plant etc.
 An entity has a set of properties called attributes, and the values for
some set of properties may uniquely identify an entity. For example,
people have names and addresses as attributes.
 An entity set is a set of entities of the same type that share the same
properties, or attributes. For example, set of all persons, companies,
trees, holidays etc.
 The individual entities that constitute a set are said to be the extension
of the entity set. Entity sets do not need to be disjoint.
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, Basic Concepts




Fig: Entity sets customer and loan
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