Systems and methods for indexing and searching the inner structure of a string over a language having a vocabulary and a grammar using bit vectors. The index preserves the inner gramatical structure of the string while allowing for a fast search. A single search provides immediate access to every level of a document, without having to re-search a single string to determine which sub-parts of that string match the search string. When a string is indexed, the index maintains a compositional representation and the grammatical relationship between the elements of the vocabulary according to the language. The string is then indexed on different levels by disregarding some of the grammatical relationships of component levels.