I am trying to create a way to tag three different fields to a set of categories. And from one field I want to know the other two fields that relate to it based on the same categories they belong to. For example, the categories are Energy, Water, and Animals. The three fields are videos, projects, and lessons. I tag the videos with the categories (more than one). I also do the same with the projects and lessons - to the same categories. Then for each video, I want to know all the projects and lessons associated with it based on the common categories. Please help.