I have a series of element in my PIAF system. These elements are naturally part of a larger application. As such, these elements need to be related to other content from my application. For example, my elements need to be associated to one or more purpose. A purpose has a series of its own properties. So the question is simple: can I associate elements in PIAF to more complex objects that are not themselves elements (or at least not elements that appear in the hierarchy)?