1. A topological index of a given set of molecules in form of a directed acyclic graph (tDAG), which contains all topologically different, connected, uncolored subgraphs of the given set of colored graphs, wherein the uncolored graphs are the vertices of the directed acyclic graph and two vertices of the tDAG are connected, when the graph corresponding to the target vertex can be derived from the graph corresponding to the tail vertex by a primitive structural transformation.