In my experience, if a management tool provides good tagging, search and sorting, it doesn't matter how the items are organized inside. Dump an item into the co

In my experience, if a management tool provides good tagging, search and sorting, it doesn't matter how the items are organized inside. Dump an item into the collection, assign tags, it joins the rest in the search and sorting. Over time, you grow and nurture your set of tags. (The exception is an outliner structure, however books wouldn't benefit from it. And directories aren't an outliner, they simply don't match the speed and convenience.) Notably, tags themselves can use a hierarchy.