input: [Member] traversal_category [Description] 
output: The ways in which the vertices in the graph can be traversed. The traversal category tags are: incidence_graph_tag, adjacency_graph_tag, bidirectional_graph_tag, vertex_list_graph_tag, edge_list_graph_tag, vertex_and_edge_list_graph_tag, adjacency_matrix_tag. You can also create your own tag which should inherit from one of the above.