Lagerpålagerprincipen

Lagerpålagerprincipen, sometimes described as the layer-on-layer principle, is a design concept used in software engineering, system architecture, and process design. It advocates organizing a system into a sequence of distinct layers, each with specific responsibilities and well-defined interfaces. Higher layers depend on the services of lower layers, while the lower layers remain independent of the higher ones.

Key aspects of the principle include clear separation of concerns, encapsulation, and loose coupling between layers. Interfaces between layers are designed to minimize knowledge of internal implementations, allowing layers to be developed, tested, and replaced more easily. Common layer stacks include presentation, application or service logic, domain models, data access, and infrastructure, though actual configurations vary by domain and project.

Benefits of applying the Lagerpålagerprincipen include improved maintainability, modularity, testability, and scalability. It supports parallel development, easier debugging, and more straightforward evolution of systems as requirements change. However, the approach can introduce complexity or performance overhead if layers are overextended or if layer boundaries are not respected. Violation of interfaces or excessive communication between non-adjacent layers undermines the principle.

Related concepts include layered architecture, separation of concerns, and clean or onion architecture. The term is used in Swedish IT literature and industry discussions as a practical guideline for organizing software and processes in a structured, modular way. Examples often show UI or API layers interfacing with application services, which in turn coordinate domain logic and data access.