The paper describes a new method of constructing semantic expansions of search requests (of generalized character) for improving the results of Web search. This method is based on the theory of K-representations - a new theory of designing semantic-syntactic analyzers of natural language texts with the broad use of formal means for representing input, intermediary, and output data. The stated approach is implemented with the help of the programming language «Java»: an experimental search system AOS (Aspect Oriented Search) has been developed.