Discovering the complex relationships between entities is one way of benefitting from the Semantic Web. This paper discusses new approaches to implementing -operators into RDF querying engines which will enable discovering such relationships viable. The cornerstone of such implementation is creating an index which describes the original RDF graph. The index is created in two steps. Firstly, it transforms the RDF graph into forest of trees and then to each tree creates its extended signature. The signatures are accompanied by the additional information about transformed problematic nodes breaking the tree structure.