Some·thing which this Aggregation is an expression of or “broadly equivalent” to.

The intended usage of this property is to point from Aggregations, which are specifically sets of Aggregated Resources, to other things which might be interchangeable in some contexts, but which are modelled differently. For example, a book might be modelled as an Aggregation of chapters, as an Aggregation of pages, or as an atomic unit; this property could be used to link between these different representations.