The invention relates to an inference machine which is used to answer questions relating to predetermined data with the aid of an ontology, which is used to structure data, and a declarative system of rules, which reproduces additional knowledge. During the evaluation of a query, inference protocols, relating to the instantiation of the regulations which appear during evaluation, are read in an evaluation unit associated with the inference unit. Explanations relating to the evaluation of the rules are generated in the evaluation unit according to the inference protocols. A logical derivation of the answer becomes transparent. The system can answer technical questions and can carry out and explain technical considerations.