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The Aarne-Thompson Classification System

Originally published by Finnish forkloristAntti Aarne and expanded by American Stith Thompson and German Hans-Jörg Uther, the Aarne-Thompson Classification System is a system for classifying folktales based on motifs.

Some Examples:
Beauty and the Beast: Type 425C
Bluebeard: 312
The Devil Building a Bridge: Type 1191
The Foolish Use of Magic Wishes Type 750A
Hansel and Gretel and other abandoned children: Type 327
Women forced to marry hogs: Type 441
The Runaway Pancake: Type 2025
Wikipedia has a complete breakdown and here has examples of most of the tale types.

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