This paper proposes a new type of relationship between layers in layered architecture and shows how to concretize the relationship between layers into design constraints. The meaning of layer relationship is explained with examples from design patterns and Microsoft COM. In addition, a prototype tool to check conformance is implemented and the architecture document of an open-source software project is checked against the actual architecture extracted from source code developed by many international developers. As a result of checking, parts that do not conform to the architecture document are investigated and it is pointed out that their modifications should be controlled with caution.