Abstract: Possibilities of query expansion with subject area thesaurus are discussed. The role of the context defined by thesaurus term links is both to refine the query and to increase the size of the sample on the query. Of particular importance is the process of expanding the query for scientific subject areas where the search based on special terminology. In this case, thesauruses of subject areas must be used to minimize the occurrence of information noise. The proposed approach takes into account the application of similar terminology in various subject areas. Examples of the use of thesaurus of separate sections of equations of mathematical physics and related fields demonstrate the effectiveness of the chosen approach of research. By linking to concepts of information resources of other areas of knowledge, the extension of the information query captures search fields of remote subject areas and various types of data, texts, symbolic, audio and video archives. Research shows that expanding the query based on context semantics improves the search quality of scientific publications in digital information and increases the effectiveness of scientific interdisciplinary research.

Abstract: In the article the meaning of terms "information", "knowledge", "thesaurus", "ontology" with reference to the sector of informatics, which studies processes of mutual transformations of the data, information and knowledge, is specified. It allows provision of short description of intellectual information systems functioning in terms of theoretical computer science.

Abstract: The problem of representation of mathematical subject domains in digital libraries and usefulness of these resources for experts is discussed. The option of representation of mathematical subject domains on the Internet is given. As information model for unit of record article of the thesaurus is chosen. Implementation of the scheme is shown on the example of the partial differential equations. Approach to the organization of information space of the author is offered, using the thesaurus by the addressee. On the basis of descriptions of subject domains of individuals creation of ontology of scientific cross-disciplinary community is supposed what, according to authors, will allow not to lose new result or opening in science, to observe priorities of authors, to build in new knowledge the settled system of classical subject domains.