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The ER model is the visual design of the database system. For efficient management and storage of data, we require the conversion of the ER model to a relational model that facilitates the storing and retrieval of data due to the format of storing in tables.

Converting an Entity-Relationship (ER) model to a relational model involves transforming the entities, relationships, and attributes depicted in the ER diagram into tables, columns, and keys in a relational database. The following are the steps that need to be followed, explained with the example of a typical college database system:

1. Identify Entities and Create Tables

Each entity in the ER model becomes a table in the relational model. The attributes of the entity become the columns of the table.

In our example, we have the following entities and respective attributes:

Student: S_Id, S_Name, Email, Age
Course: C_Id, C_Name, C_Prof
Professor: P_Id, P_Name, Email, Dept.

We can separate the S_Name and P_Name attributes into S_FirstName, S_LastName and similarly for the Professor table to create atomic attributes. For simplicity, we will stick to multivalued attributes only in this article.

2. Key Selection

Choose the primary key for each table. For some, it can be in the form of a composite key (Weak entity).

In our example, we can have S_Id, C_Id, and P_Id as primary keys for the Student, Course, and Professor tables respectively, since they would satisfy the unique and non-null property constraints.

3. Identify Relationships and Create Foreign Keys

If entities have relationships, break them down and reduce the tables if possible. Relationships in the ER model are represented by foreign keys in the relational model. Below are the handling mechanisms for different types of relationships:

1-1 Relationship: 2 tables; the primary key can lie on any side.
1-Many Relationship: 2 tables; the primary key can lie on the many side.
Many-1 Relationship: 2 tables; the primary key can lie on the many side.
Many-Many Relationship: 3 tables; the primary key lies in the relation table having primary keys from both tables acting as foreign keys.

In our example, we have the following relationships:

Enrollment (between Student and Course): A student can enroll in multiple courses, and a course can have multiple students (many-to-many relationship). So we would create a separate enrollment relationship table.
Enrollment Table: S_Id (FK), C_Id (FK), E_Date
Primary Key: Composite key consisting of S_Id and C_Id.
Teaching (between Instructor and Course): A professor can teach multiple courses, but a course is typically taught by one professor (many-to-one relationship). Hence, here we would have the primary key on the Course Table.
Course Table (updated):