You are putting the horse behind the buggy. Ignoring the link table, how do you know which row in the topic table is a topic and which a subtopic and which subtopic is a subtopic of which parent topic? You need the order Horse, Whip, Buggy. Nothing will work if you do not have your parts in the right order (that is, having the buggy in the front, followed by the whip and then the horse will not result in much of use, nor will putting the whip behind the buggy even if the horse is out front be of much use, because whipping the buggy will not make the horse go faster). You need to deal with your topic/subtopic first, before you can even bother considering linkages to topic/subtopic. In other words you need to write the book before worrying about what the biographie that someone will use to refer to it will look like.