Vladimir Propp (1895 - 1970) was a scholar who was interested in stories we tell as a culture. He analyzed the basic structure that underlines a story by looking at aural/fairytale culture. He particularly looked at Russian folk tales to identify their simplest narrative elements.
He looked at these stories and found commonalities among them. He also observed the forms & shapes that each story takes. Looking at the functions of a story (the aspects to a story). For example, boy meets girl, boy looses girl etc.
He came to the conclusion that there are 31 aspects to a story, with the last one always being 'they all lived happily ever after. The end. ' Furthermore, within each genre you expect certain things to occur. For example, with comedy you expect a lighthearted, funny film.