Converting ER Models to Relational Models: A Step-by-Step Guide

Learn how to transform Entity-Relationship (ER) models into relational schemas, providing a bridge between the conceptual design and the implementation of a database. This guide will cover the key steps and considerations involved in the conversion process, ensuring that the relational schema accurately reflects the data relationships defined in the ER model.

Convert ER Model to Relational Model

The ER Model, when represented through diagrams, provides a clear overview of entity-relationships that is easier to comprehend. ER diagrams can be mapped to a relational schema, enabling the creation of a relational schema based on an ER diagram. Although not all ER constraints can be directly imported into the relational model, an approximate schema can be generated.

Various processes and algorithms exist to convert ER Diagrams into Relational Schema. Some of these processes are automated, while others are manual. Here, we will focus on mapping the contents of the diagram to relational basics.

Components of ER Diagrams

ER diagrams primarily consist of:

  • Entities and their attributes
  • Relationships, which represent associations among entities

Mapping Entity

An entity represents a real-world object with specific attributes.

Mapping Process (Algorithm)

  1. Create a table for each entity.
  2. Convert the entity's attributes into fields of the table, specifying their respective data types.
  3. Declare a primary key.

Mapping Relationship

A relationship signifies an association among entities.

Mapping Process

  1. Create a table for the relationship.
  2. Add the primary keys of all participating entities as fields in the table, along with their respective data types.
  3. If the relationship has any attributes, include each attribute as a field in the table.
  4. Declare a primary key that comprises all primary keys of the participating entities.
  5. Declare all foreign key constraints.

Mapping Weak Entity Sets

A weak entity set is one that does not possess a primary key associated with it.

Mapping Process

  1. Create a table for the weak entity set.
  2. Add all its attributes to the table as fields.
  3. Include the primary key of the identifying entity set.
  4. Declare all foreign key constraints.

Mapping Hierarchical Entities

ER specialization or generalization appears in the form of hierarchical entity sets.

Mapping Process

  1. Create tables for all higher-level entities.
  2. Create tables for all lower-level entities.
  3. Add primary keys of higher-level entities to the tables of lower-level entities.
  4. In the lower-level tables, add all other attributes of lower-level entities.
  5. Declare the primary key for both the higher-level and lower-level tables.
  6. Declare foreign key constraints.