Your Nouns Are Not Your Architecture

A common way to design an application is to begin with its nouns: User Product Order Payment Then each noun receives the standard architectural starter pack: UserController UserService UserRepository The controller receives users, the service services them, and the repository stores them somewhere responsible. This is noun-oriented architecture : treating every important thing in the domain as if it were automatically a useful software boundary. It works for simple CRUD systems. Unfortunately, most applications eventually do something. The noun becomes a drawer Consider a typical UserService : register() findByEmail() resetPassword() changeAddress() disableAccount() mergeAccounts() assignRole() calculateDiscount() These operations all involve a user. That is approximately where their similarity ends. They have different rules, dependencies, side effects, security concerns, owners, and reasons to change. They live together because User was the nearest available noun when the folders were created. As more behaviour accumulates, UserService becomes the official location for anything vaguely user-shaped. Other components depend on it. It gradually depends on authentication, email, permissions, billing, auditing, and several services added during incidents nobody wishes to revisit. The noun becomes both a dependency of everything and a consumer of everything. The folder remains impressively tidy. Name the capability, not the material A better starting question is not: What things exist in this system? It is: What must this system be capable of doing? That leads to components such as: UserRegistrar PasswordResetter AccountMerger OrderPlacer PaymentRefunder SubscriptionCanceller These are agentive names . They name the component responsible for performing a capability. Compare: UserService with: PasswordResetter UserService tells us which noun is nearby. PasswordResetter tells us what the component is for. That difference produces better architectural questions: What rules