It is also possible to restrict the cut operations to 2-cuts at the expense of a larger set of "base graphs" that provide building blocks to construct more linear branched monocyclic spiro polycyclic Figure : A minimal set of base graphs B needed to access all graphs of degree at most 4 using a sequence of natural join operators. complex scaffolds. We restrict the following discussion to graphs with degree at most 4, which in essence covers the search space of organic molecules. Starting point is the set of graphs B shown in Fig. .