A.M. Namestnikov - Ph.D. (Eng.), assistant professor Department of Information Systems, Ulyanovsk State Technical University. E-mail: nam@ulstu.ru
R.A. Subkhangulov - post-graduate student, Department of Information Systems, Ulyanovsk State Technical University. E-mail: subkhangulov-ruslan@yandex.ru

Indexes are traditionally applied to the analysis of a very big set of text documents in the form of the inverted lists and their various modifications. For tasks of the intellectual analysis of the technical documentation which decisions are based on domain area in the form of ontology, representation of indexes in the form of the inverted lists can't be considered. Any traditional index of a text documents repository is based only on internal properties of information resources. It is possible to carry frequencies of occurrence of terms to such properties in documents. Conceptual indexing of technical documentation in electronic archive assumes submission of the document in system of coordinates which is a domain ontology. It is possible to create of the formal description of a conceptual index for electronic archive of the design organization. Each document in electronic archive is described by a set of concepts of domain ontology which dominate in the document. Thus, possessing information on a class of concepts of ontology (a profile of the designer), it is possible to execute specification of search queries by those terms which are included in the corresponding terminological environments of the ontology concepts. The idea of a conceptual index of electronic archive assumes that any text document is submitted a set of concepts which don't depend from each other. Proceeding from this assumption the conditional probability of the document is approximated by work of conditional probabilities of all concepts in the document.