Computer Science – 8.1 Database Concepts | e-Consult

An Entity-Relationship Diagram (ERD) is a visual representation of the entities (real-world objects or concepts) and the relationships between them in a database. It's a high-level design tool used to conceptualize the database structure. A relational database schema, on the other hand, is a detailed blueprint of the database, specifying the tables, columns, data types, primary keys, and foreign keys. It's the actual implementation plan for the database.

Purpose of an ERD:

• To provide a visual overview of the database structure.
• To facilitate communication between stakeholders (e.g., database designers, developers, and users).
• To identify potential data requirements and relationships.
• To serve as a basis for designing the relational database schema.

Example ERD for a Library Database:

In this ERD, the entities are Book, Member, and Loan. The relationships are represented by the lines connecting the entities. For example, a Book can be borrowed by a Member (represented by the relationship between Book and Loan). The attributes are listed within each entity.

Deriving a Relational Database Schema from an ERD:

1. Each entity in the ERD becomes a table in the relational database.
2. Attributes of the entity become columns in the table.
3. The primary key of the entity becomes the primary key of the table.
4. Relationships between entities are implemented using foreign keys. For example, the Loan table would have foreign keys referencing the Book and Member tables to represent the relationships between them.