Bce

Pattern

• structure code using the Boundary-Control-Entity (BCE/ECB) pattern
• the unit of organization is the business component (BC); each BC owns a responsibility and is composed of one or more layers
• the three layers are boundary, control, entity; each has a distinct responsibility (see layer sections below)
• do not explain the BCE pattern in generated documentation

Package / Directory Structure

• package or directory path: [ORGANIZATION].[PROJECT].[BC].[boundary|control|entity]
• the top-level package reflects the application responsibility or name
• business components are direct children of the top-level package and named after their responsibilities
• the boundary, control, entity segments are only allowed inside a business component
• name packages after their domain responsibilities, not technical concerns

Business Components (BC)

• a BC may represent a domain concept or a shared concern; both are valid when the responsibility has a name and is reused
• a BC does not need every layer; a BC may consist of only a control layer when its responsibility is procedural and consumed by other BCs
• not every BC needs a dedicated boundary; control contents may be consumed directly when no facade is justified
• prefer a dedicated BC over the root application package when a shared concern carries domain or protocol semantics, exposes more than one operation, or is expected to grow
• reserve the root application package for trivial single-class plumbing with no business semantics and no protocol coupling
• create new BCs with minimal logic and essential fields only

Boundary Layer

• keep coarse-grained classes in the boundary
• place facades that adapt external protocols, transports, or UI events to internal operations in the boundary
• boundary classes are the only entry points called from outside the system; external actors (UI, protocols, transports, tests) never reach control or entity directly
• cross-cutting concerns that wrap an operation (transactions, authorization checks, request/response mapping) belong in the boundary, not in control or entity

Control Layer

• implement procedural business logic in the control layer
• prefer stateless, function-like units for procedural logic
• control may be called by the boundary of the same BC or directly by other BCs; the boundary is not a gate for cross-BC calls

Entity Layer

• maintain domain objects, data classes, and entities in the entity layer
• entities maintain state and corresponding behavior; they are not anemic data holders
• model value objects as enums or equivalent closed sets where the language supports them
• direct references between entities from independent BCs are allowed, but always aim for Maximal Cohesion and Minimal Coupling between BCs
• if a relation exists in the persistent store (e.g. foreign key), the entities must carry a corresponding reference (id field or association); the schema is the source of truth
• excessive cross-BC references or shared configuration is a refactoring signal — split, merge, or rebalance the BCs to restore cohesion

Naming

• name classes, modules, and files after their responsibilities
• avoid meaningless suffixes (e.g. *Impl, *Service, *Manager, *Creator)
• a class or module name must not end with Control
• reserve protocol- or pattern-specific suffixes (e.g. Resource, Factory, Builder) for elements that actually fulfill that role

Documentation

• document only domain-specific packages where the purpose is not self-evident
• when documenting a top-level package or BC, describe design decisions and responsibilities — not contents
• in Java, use package-info.java with JavaDoc to document packages
• do not write documentation that restates the BCE pattern itself

Composition with Other Skills

• this skill defines only the architectural pattern; language, framework, build, testing, and protocol rules come from the composed skill (e.g. microprofile-server, web-components, aws-cdk, java-cli-app)
• when a composed skill adds a layer rule (e.g. "health checks belong in boundary", "JAX-RS resources are boundary classes"), apply it on top of the BCE rules above; the composed skill always specializes, never contradicts