14. The method according to claim 1 , wherein a structure in the structure dictionary takes a form of a word built using an alphabet of symbols taking a form of constants corresponding to at least one of alpha-numeric strings and characters, and variables corresponding to at least one generic data type, the word being built using formation rules of a formal language, the method of building the structure sub-collection of values matching said word comprising: storing portions of values corresponding to the same symbol in the same symbol sub-collection, the values matching the word, the portions matching the symbol while parsing the values along the structure of the word; and storing the structure sub-collection in a form of the symbol sub-collections corresponding to all particular symbols from which the word is formed using the formation rules.
14. The method according to claim 1 , wherein a structure in the structure dictionary takes a form of a word built using an alphabet of symbols taking a form of constants corresponding to at least one of alpha-numeric strings and characters, and variables corresponding to at least one generic data type, the word being built using formation rules of a formal language, the method of building the structure sub-collection of values matching said word comprising: storing portions of values corresponding to the same symbol in the same symbol sub-collection, the values matching the word, the portions matching the symbol while parsing the values along the structure of the word; and storing the structure sub-collection in a form of the symbol sub-collections corresponding to all particular symbols from which the word is formed using the formation rules. 25. The method according to claim 14 , wherein the word belonging to the structure dictionary is modifiable and methods of modifying the word include at least one of: detecting symbols in the word that can be replaced by more detailed sub-words, automatically adding new words obtained by replacing the symbols in the structure dictionary by the sub-words, or recommending the new word to a user of the relational database system via an interface, the user deciding whether to add the new word to structure dictionary and whether to replace the word with the new word in the structure dictionary; evaluating the candidate replacements of symbols by more detailed sub-words based on a group of criteria including at least one of minimizing the number of structure sub-collections and minimizing the cost of storing symbol sub-collections; and providing an interface to a user of the relational database system, the interface reporting amounts of values matched by new words obtained by replacing symbols by more detailed sub-words and sizes of symbol sub-collections corresponding to symbols of the more detailed sub-words, the user using the interface to add the new words to the structure dictionary and to remove the word from the structure dictionary.