In this study we developed a method of decomposing a given schematic diagram into parts, without knowledge of drawing rules of specific diagrams. The parts to be extracted should be adequate from perceptual point of view of human beings. The method combines line-based and region-based algorithms. The result of decomposition is stored in a hierarchical data structure, reflecting the hierarchical nature of the algorithm. If two or more related diagrams are available, for instance, those illustrating the movement of an mechanical system such as an engine, then we may limit the possibilities of decomposition further or correct erroneous decomposition.