We consider the problem of searching for similar patterns in terms of graph theory. It classifies the main cases of partial isomorphism of two connected undirected graphs. Determined step by step procedure of differentiation of graph vertices to find the highest isomorphic subgraph. A method for assessing the structural similarity based on the search for a common sub-graph and determining the functions of the distance between the graphs.
connected undirected graph, isomorphism, graph invariant, the greatest common subgraph, differentiation of vertices, metric characteristics