 It is somewhat analogous to the Aarne–Thompson classification system or motif-index for folktale studies, except that each ballad can only have one TSB No., whereas any given folktale can exhibit several motifs.The TSB divides its list of types into six groups (with some subgroups), as below.The division essentially follows the one by A. I. Arwidsson, and Svend Grundtvig's original division in "Danmarks gamle folkeviser" (DgF); however, many of the ballads Grundtvig placed in group C have been reclassified.