When I encounter a system or data design decision I'm unsure about, I endeavor to ask the same thing: where does authority live, and how bounded is it?
Where Authority Belongs
Authority in a software system is the assignment of decision-making power. Something is authoritative over data when it is the canonical source of truth, and authoritative over a behavior when it is the only thing that can legitimately enforce it. The belief of where authority belongs shapes what the system can absorb when it changes and what it cannot.
The best practices across software engineering are each a response to a specific observed failure. The Single Responsibility Principle observed that a class holding authority over two concerns forces reasoning about both when either changes, producing behavioral drift at the class level. Database normalization observed that a fact stored in two places produces an inconsistency when one is updated, causing data drift. Least privilege observed that a process able to affect state beyond its concern eventually does, introducing state drift at the execution level. Bounded contexts observed that two teams sharing a term without shared authority over its meaning will diverge on that meaning, creating semantic drift at the domain level.
