With development of knowledge bases (KB) there appeared expert systems that use KBs to support them in decision making process. Decision Support Systems, that are the subject of the paper, communicate with knowledge bases by populating them with known facts and receiving newly inferred knowledge. However there exist situations when a DSS receives ambiguous response from knowledge base and needs to know what additional information is missing and is required to give a precise response. The paper focuses on a communication between a DSS and a knowledge base especially in the scope of getting the missing information. The special type of inference performed over a Description Logics ontology to solve the problem, the corresponding query and implementation issues are described.