Skip to content

Small Business ERD

Run the ERD MicroSim Fullscreen

About This MicroSim

A canonical small-e-commerce ERD with five entities: Customer, Order, OrderLine (the join table), Product, and Supplier. The diagram demonstrates the most common pattern in business databases: the many-to-many relationship between Order and Product resolved via an OrderLine join entity.

Click any entity to see what it represents, why each attribute exists, and a sample row. Click any relationship line for the plain-English cardinality. Toggle Show Normal-Form Watch-Outs to surface common 1NF/2NF/3NF traps.

Embedding This MicroSim

<iframe src="https://dmccreary.github.io/information-systems/sims/small-business-erd/main.html"
        height="722px" width="100%" scrolling="no"></iframe>

Lesson Plan

Learning Objectives

By the end of this activity, students will be able to:

  1. Read a Crow's Foot ERD and identify primary keys and foreign keys
  2. State each cardinality in plain English
  3. Recognize where a join entity is required for a many-to-many relationship
  4. Identify common 1NF, 2NF, and 3NF violations

Suggested Activities

  1. Cardinality Drill (10 min) — For each line, state the cardinality both directions
  2. Normal-Form Audit (15 min) — Toggle watch-outs; propose a fix for each
  3. Add an Entity (15 min) — Add a Shipment entity. Where does it connect, and what FKs does it need?

References

  • Codd, E. F. (1970). A Relational Model of Data for Large Shared Data Banks.
  • Date, C. J. (2003). An Introduction to Database Systems, 8th ed.