In this paper we assume there is a group of connected information systems forming distributed information system (DS). They work under the same ontology. At the same time, each information system has its own knowledge base. Values of attributes in each information system S form atomic expressions of a language used for communication with others. Collaboration among them is initiated when one of information system S is asked by user to resolve a query containing some nonlocal attributes for S. Therefore it has to contact other information systems to obtain additional, helpful knowledge for finding finally objects satisfying given query. Because there is a set of different information systems connected with a given one, we have to decide which of them is the closest with its knowledge, and which one should be selected by user, for further investigation.