Discuss the basic concepts of Entity Relationship (ER) Model. Illustrate as to how an ER model is diagrammed.

Entity Relationship (ER) data model is proposed by Perter Pin-Shan Chen in 1976. This model is developed using DBMS to frame an application database. The ER model is a generalisation of old hierarchal and network approach models. This model describes data in terms of the following elements.

  1. Entities
  2. Attributes
  3. Relationship between entities

These major elements of ER model are used to express a real world situation (reality) for which a database is to be designed. The database structure using the ER model can be shown diagrammatically with the help of ER diagrams. There are different symbols that are used to represent different types of entities, attributes, identifiers and relationships.

Major Elements of ER Model

Represented as (Symbols)

Entity Type is represented by a rectangular box

Weak Entity Type is represented by a double-lined rectangular box

Relationship Type is represented by a diamond-shaped box

Identifying Relationship Type is represented by a double-lined diamond-shaped box

Attribute Name is enclosed in ovals and are attached to their entity type with the help of straight lines

Key Attribute Name enclosed in ovals and attached to their entity type by straight lines.

Multi-valued Attributes are represented by double ovals.

Derived Attributes are represented by dashed line Ovals

Total Participation of E2 in R is represented as

Cardinality Ratio 1 : N for E1 : E2 in R is represented as

 

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