Theory only sticks when you build something. Model five real systems — a library, a university, a hospital, an online store and a hotel — and check your diagram against a worked answer.
This is the full written version of an interactive, slide-by-slide lesson deck used in teaching. Everything covered in the deck is below — open the interactive version to work through it with live diagrams, worked examples and a practice quiz where included.
A library lends books to its members. Each book has an ISBN, title, and genre. Each member has a member ID, name, and email address.
A member can borrow multiple books over time, and the same book may be borrowed by many different members. Each borrowing transaction records a borrow date and a return date.
A university manages student enrollments in courses. Each student has a student ID, full name, and GPA. Each course has a course code, title, and number of credits.
Students can enroll in multiple courses each semester, and each course can have many students enrolled. The enrollment records the semester and grade the student received.
A hospital manages doctors, patients, and departments. Each doctor has a doctor ID, name, and specialization. Each patient has a patient ID, name, and date of birth. Each department has a department ID and name.
Each doctor works in exactly one department (a department has many doctors). Doctors can treat many patients, and patients may be treated by many doctors. Each treatment records a treatment date.
An online store tracks customers, their orders, and products. Each customer has a customer ID, name, and address. Each product has a product ID, name, and unit price. Each order has an order ID and order date.
A customer can place many orders (each order belongs to one customer). An order can contain multiple products, and a product can appear in many orders. Each order-line records the quantity ordered.
A hotel manages guest reservations for its rooms. Each guest has a guest ID, full name, and phone number. Each room has a room number, room type (single/double/suite), and nightly rate.
A guest can book multiple rooms over different stays, and the same room can be booked by many guests across different periods. Each booking records a check-in date and a check-out date.
Work from a written scenario. Underline the nouns to find candidate entities, underline the descriptive phrases to find attributes, and underline the verbs connecting nouns to find relationships. Then decide cardinality by asking, for each side, whether one instance can relate to more than one on the other side.
Read it back as sentences and check it against the original scenario: every fact the scenario states should be expressible from the diagram, and every entity should have a key attribute. If a requirement cannot be read off the diagram, something is missing; if a shape does not correspond to anything in the scenario, it is probably invented.
The interactive deck adds live diagrams, step-by-step reveals and practice activities that this written version can't carry.