Disk/band surface and spatial-graph homology

Using disk/band surfaces, we investigate spatial-graph homology. A necessary and sufficient condition for spatial embeddings of a graph to be homologous is expressed in terms of disk/band surfaces. By this condition we can decide practically whether two given spatial embeddings are homologous or not. We equip the set of spatial-graph homology classes with an abelian group structure and give a method to calculate this group by using the condition above.