Just a collection used to built on

Thompson’s Motif-Index is one of the most important works in folklore
studies produced in the twentieth century. Some may view it merely as a taxonomic endeavor, but as Thompson stated, “Before it can become an object of serious and well-considered study, every branch of knowledge needs to be classified. There was a time when geology and botany consisted of random collections of facts and hastily constructed theories. It was only when this anecdotal stage gave way to systematic classification that real progress was made toward a thorough method of study” (1977, 413).

Archetypes and motifs in folklore and literature : a handbook / edited by Jane Garry and Hasan El-Shamy