I get you, but I just think that prerequisite knowledge is often not going to be chronologically published. I was thinking along the lines of the Netflix recom

I get you, but I just think that prerequisite knowledge is often not going to be chronologically published. I was thinking along the lines of the Netflix recommendation engine based on topics covered in a text and the overall 'grade level' of the book. There's been some good work done in the latter, eg "The Art of Plain Talk" which has a system for analyzing the grade level of a given piece of writing.