Architecture conformance checking is an important activity of architecture enforcement where the architect ensures that all architecture concepts are implemented correctly in the source code. In order to support the architect, a lot of tools for conformance checking are available that allow to formalize the architecture in order to perform an automated verification. Typically, the formalization uses a rigid, tool-specific architecture concept language that may strongly deviate from the project-specific architecture concept language. In addition, a high level of formal expertise is required in order to comprehend the created formalization. We present an approach that uses a controlled natural language for the formalization of architecture concepts. This language allows to flexibly express architecture rules directly with project-specific concepts. Consequently, the resulting formalization is easy to understand and might also be used as an architecture documentation at the same time. Nevertheless, the documentation can be automatically verified, since the approach is based on powerful means of the semantic web, i.e., ontologies and description logics. For the evaluation of the approach, we use the real-world software system TEAMMATES and show that architecture rules and concepts can be flexibly designed and checked for conformance in order to detect crucial architecture violations.