The conceptual modelling of software architectures is of central importance for the quality of a software system. A rich modelling language is required to integrate the different aspects of architecture modelling, such as architectural styles, structural and behavioural modelling, into a coherent framework. We propose an ontological approach for architectural style modelling based on description logic as an abstract, meta-level modelling instrument. Architectural styles are often neglected in software architectures. We introduce a framework for style definition and style combination. The link between quality requirements and conceptual modelling of architectural styles is investigated. The application of the ontological framework in the form of an integration into existing architectural description notations such as ACME and UML-based approaches, and also service ontologies is illustrated.