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.
- Entities
- Attributes
- 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 |
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Weak Entity Type is represented by a double-lined rectangular box |
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Relationship Type is represented by a diamond-shaped box |
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Identifying Relationship Type is represented by a double-lined diamond-shaped box |
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Attribute Name is enclosed in ovals and are attached to their entity type with the help of straight lines |
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Key Attribute Name enclosed in ovals and attached to their entity type by straight lines. |
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Multi-valued Attributes are represented by double ovals. |
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Derived Attributes are represented by dashed line Ovals |
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Total Participation of E2 in R is represented as |
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Cardinality Ratio 1 : N for E1 : E2 in R is represented as |