what is ER model in DBMS?

 

What is the E-R model?

E-R ( Entity Relationship ) model

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• An E-R model was proposed by Peter Chen in 1971.
• An Entity-relationship model describes the structure of a database.
• An ER model is a design or blueprint of a database.
• An E-R model is a high-level data model. it is used to define the data elements and relationships for a specified system.
• An ER model defines the conceptual view of a database.

 ER Diagram

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Suppose we design a college database. In this database, the student and college will be an entity with attributes like address, name, id, age, clg_id, clg_name, etc.

Geometric shapes and their meaning in an E-R Diagram:- 

Rectangle: Represents Entity sets.
Ellipses: Attributes
Diamonds: Relationship Set
Lines: They link attributes to Entity Sets and Entity sets to Relationship Set
Double Ellipses: Multi-valued Attributes
Dashed Ellipses: Derived Attributes
Double Rectangles: Weak Entity Sets

Components of an ER Diagram

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there are three basic concepts

1. Entities
2. Attribute
3. Relationship

Entities: A real-world thing either living or non-living that is easily recognizable and nonrecognizable. An entity may be any object, class, person, or place. an entity can be represented as rectangles.

Attribute: The attribute is used to describe the property of an entity. Eclipse is used to represent an attribute.

For example, id, age,  name, address, clg_id, clg_name, etc. can be attributes of a student and college.

Relationship:  A relationship is used to describe the relation between entities. Diamond is used to representing the relationship.

Types of relationships: there are many types of relationships.

1. one–to–one relationship
2. one–to–many relationships
3. many–to–one relationship
4. many – to – many relationships