A supporting subdomain can also turn into a core subdomain—for example, if a company finds a way to optimize the supporting logic in such a way that it either reduces costs or generates additional profits.

The typical symptom of such a transformation is the increasing complexity of the supporting subdomain’s business logic. Supporting subdomains, by definition, are simple, mainly resembling CRUD interfaces or ETL processes. However, if the busi‐ ness logic becomes more complicated over time, there should be a reason for the additional complexity. If it doesn’t affect the company’s profits, why would it become more complicated? That’s accidental business complexity. On the other hand, if it enhances the company’s profitability, it’s a sign of a supporting subdomain becoming a core subdomain.