How do you model business data?

Direct answer

What a strong answer covers

How it works

Modelling starts from the business, not the database: which things exist, what identifies each of them stably, how they relate and in what cardinality, how they change over their lifetime, who owns each fact, and what must always be true. History and privacy are decided up front, since knowing what an address was last year or being able to delete a person’s data are structural. The conceptual model is validated with domain experts through examples; only then is it mapped to tables, documents, or events with the query and write patterns in mind, keeping one source of truth per fact.

Example

For a subscription business the conceptual model separated Customer, Account, Subscription, and Plan, with a Subscription having a history of plan changes rather than a mutable plan field; that decision came from the question of what a customer was paying in March. The physical model then stored subscription periods as rows with valid-from and valid-to, and the invoicing query became a simple range join.

Common mistakes

• Modelling from the screens and ending up with one table per form.
• Using a natural key such as email as the identity and then supporting email changes.
• Overwriting history because the model has no notion of time.

A useful answer structure

Answer from your own work.

Do not memorise a script: use only examples you can explain honestly in follow-up questions.