ER TO RELATIONAL MAPPING

 

 ER to Relational Mapping

ER to Relational Mapping is the process of converting an Entity-Relationship (ER) model into relational tables. After designing the database using an ER diagram, it must be transformed into a relational schema that can be implemented in a relational database system.

This step is important because relational databases store data in the form of tables, not diagrams.

🔹 Mapping Rules

1️⃣ Mapping Strong Entity

  • Each strong entity becomes a separate table.

  • Attributes of the entity become columns.

  • The primary key of the entity becomes the primary key of the table.

2️⃣ Mapping Weak Entity

  • Create a separate table for the weak entity.

  • Include the primary key of the strong entity as a foreign key.

  • Combine both keys to form a composite primary key.

3️⃣ Mapping One-to-One (1:1) Relationship

  • Add the primary key of one entity as a foreign key in the other table.

  • Preferably add it to the table with total participation.

4️⃣ Mapping One-to-Many (1:N) Relationship

  • Add the primary key of the “one” side as a foreign key in the “many” side table.

5️⃣ Mapping Many-to-Many (M:N) Relationship

  • Create a new table for the relationship.

  • Include primary keys of both entities as foreign keys.

  • Combine them to form a composite primary key.

6️⃣ Mapping Multivalued Attribute

  • Create a separate table for the multivalued attribute.

  • Include the primary key of the original entity as a foreign key.

🔹 Importance

  • Converts conceptual design into implementation-ready structure

  • Maintains relationships and constraints

  • Ensures proper database design

ER to Relational Mapping is a crucial step in database development, bridging the gap between design and actual database implementation.

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