Apart from “collection” and “item” levels there is often a further level, described as “sub-item” level. While many things can be described as a single object (e.g. a photo, a statue) sometimes they can be made up of component parts: a book has chapters, a documentary has scenes, a musical score has movements, a relational database has tables, and so on. To find a particular component requires not just the “item-level” metadata but also its “sub-item” or “component” level metadata. Obviously this increases the effort required, but it allows for much better searching and can save a lot of time later.