Sample diagrams for designing databases and data warehouses: entity-relationship models in crow's foot and Chen notation, a cardinality guide, a logical schema with keys and indexes, a star schema and a Data Vault. Each page is a complete, realistic example you can copy.
UML covers software structure and behaviour; these are the other standard notations used alongside it. Database work relies almost entirely on entity-relationship (ER) style diagrams, because the questions are about data: what is stored, how rows relate, and which keys and constraints hold it together. UML class diagrams can describe data too, but ER notation shows keys and cardinality more directly and is what DBAs, data engineers and modelling tools expect.
The section moves from concept to warehouse. A Chen or crow's foot ER diagram captures the business concepts. A logical schema adds columns, data types, primary and foreign keys and indexes, ready to become DDL. On the analytics side, a Data Vault integrates many sources with full history, and star schemas present that data to BI tools in an easy-to-query shape.
Every sample page shows one realistic diagram, a step-by-step walkthrough, a legend, a variant, pros and cons, and the same model as Mermaid or PlantUML code.
| Question | Diagram | Sample page |
|---|---|---|
| What things exist and how do they relate? | Crow's foot ER diagram | Online Shop ER Diagram |
| What is a weak entity or a relationship attribute? | Chen ER diagram | Library ER Diagram (Chen) |
| Is this relationship optional, one or many? | Cardinality line endings | Cardinality: Crow's Foot Guide |
| Which columns, types, keys and indexes do we build? | Logical schema diagram | Logical Schema Diagram |
| How will analysts slice sales by date, product and store? | Star schema | Star Schema Diagram |
| How do we integrate many changing sources with history? | Data Vault model | Data Vault Model Diagram |
Most real projects use two or three of these together: an ER diagram for the operational database, then a star schema (and sometimes a Data Vault) for the warehouse fed from it.