The scientific term for this description of organisms is taxonomy. If phylogeny is to be also reconstructed (these reconstructions are displayed in family trees), this is called systematics.
The systematics of sharks are complicated and mainly aligned along anatomical outer features of the different shark species. Since evolution cannot be observed, we can only try to reconstruct their phylogeny step by step. Every fossil classification may have to be reworked when new insights are gained, and every feature may contribute to that. Therefore, the systematics are ever-changing and family trees need to be updated with each new insight gained.
(Photos: F.Hajek, C.Gstoettner)