Understanding the Entity Relationship Diagram

Entity Relationship Diagrams are powerful tools used in database design to visually represent the relationships between different entities within a system. They help in understanding the data structure and the interactions between various components, making them essential for both business analysts and developers.

What is an ERD?
An ERD is a type of flowchart that illustrates how entities such as people, objects or concepts relate to each other within a system. It uses symbols like rectangles for entities, diamonds for relationships, and lines to connect them, indicating how data is interrelated.

Components of an ERD

• Entities. These are objects or concepts, such as “Patient”, “Doctor”, or “Medical Record”.
• Relationships. These depict how entities interact, such as a “Doctor’s Appointment” being scheduled by a “Patient”.
• Attributes. These are properties or details of entities, like a patient’s name or a doctor’s specialty.
• Cardinality. This shows the numerical relationship between entities, indicating how many instances of one entity relate to another.

Case Study: Medical Appointment System
Let’s explore the ERD representing a medical appointment system.
Patient. Can schedule multiple doctor’s appointments, but each appointment is linked to only one patient.

• Doctor’s Appointment. Is booked by a patient and involves a doctor.
• Doctor. Can have multiple appointments and is responsible for prescribing test directions.
• Medical Record. Each patient has one, which can be read and updated by doctors.
• Lab Attendant. Updates results based on prescribed test directions from doctors.

Key Relationships

• Patient - Doctor's Appointment: A patient can schedule multiple appointments (one-to-many relationship).
• Doctor - Doctor's Appointment: A doctor can have multiple appointments (one-to-many relationship).
• Doctor - Medical Record: Doctors can read and update medical records (one-to-many relationship).

Doctor - Lab Attendant: Doctors give test directions to lab attendants, who then update the results.