Abstract. In the paper we propose a method of structuring a knowledge base into hierarchically related contexts and present how this arrangement influences the structure of TBox and ABox. We introduce a possibility to attach to a single TBox many ABoxes describing different parts of a domain and we show how to interpret such an ontology. Practical application of the method offers very interesting possibilities, like shortening the time of inference or storing mutually contradictory pieces of information in a single knowledge base. We analyse how such a structure changes purpose and mechanisms of reasoning, and we discuss their soundness and completeness. We also describe some related work about contexts.