There's four. Ok we can use 2 categories and 1 type to absorb 3 of them but what about the fourth? Let's say we put it in 70's and Pop categories wiih Musical as the Type where do we put No1? Perm these any way you like and you always get the same answer -  the presenter can only search the category field (Type is simply a list). None of the others are visible. I accept we can schedule on any field but we cannot search on them, so let's assume a presenter wants to do No1 songs from the 70's. How do they filter them out? - Can't is the simple answer.