Reduction of ER Diagram to Table

Reduction of ER Diagram to Table

In database design, an Entity-Relationship (ER) diagram is a powerful tool used to visually represent the structure of a database. However, for actual implementation, we need to convert the ER diagram into a set of relational tables. This process is known as the reduction of an ER diagram to table format.

This article walks you through the essential steps of reducing an ER diagram to a collection of relational tables, following a structured and logical approach.

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Converting ER Diagram to Tables

Each component of the ER diagram—entities, attributes, and relationships—can be systematically translated into tables and columns. Below are the key principles used in this transformation:

1. Entity Types Become Tables

Each collection of entities in the ER diagram is transformed into its own table.In the given diagram, the entities LECTURE, STUDENT, SUBJECT, and COURSE are represented as individual tables.

2. Single-Valued Attributes Become Columns

A column in the corresponding table is created for each attribute that has a single value per entity instance.

• For STUDENT, the columns are: STUDENT_ID, STUDENT_NAME
• For COURSE, the columns are: COURSE_ID, COURSE_NAME
• For other entities, the same reasoning holds true.

3. Key Attributes Become Primary Keys

Each entry is uniquely identified by a key attribute, which also serves as the table’s primary key.In the ER diagram, COURSE_ID, STUDENT_ID, SUBJECT_ID, and LECTURE_ID are primary keys for their respective tables.

4. Multivalued Attributes Require Separate Tables

Multivalued attributes cannot be stored in a single column, so a separate table is created.

• Example: The HOBBY attribute in the STUDENT entity.
  A new table STUD_HOBBY is created with columns STUDENT_ID and HOBBY.
  Together, these columns form a composite primary key.

5. Composite Attributes Are Split Into Components

Composite attributes are broken down into their atomic parts.

• For example, ADDRESS is a composite attribute of STUDENT and includes:
  DOOR#, STREET, CITY, STATE, and PIN.
  These are stored as individual columns in the STUDENT table.

6. Derived Attributes Are Not Stored

Derived attributes are not included as table columns.

• The AGE attribute is derived from the DATE_OF_BIRTH.
  Since it can be calculated when needed, it is not stored in the STUDENT table.

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Final Table Structure

Following these steps, the ER diagram is reduced to a set of normalized relational tables. Each table clearly maps to an entity or relationship from the original ER diagram, preserving data integrity and enabling efficient querying.

This structured approach ensures the transition from conceptual design to physical implementation is smooth and logically sound.

For more such foundational database concepts and tutorials, stay tuned with UpdateGadh—your trusted guide for all things tech.

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