This class is used to relate two Locations to each other. This mechanism can be used to indicate how more finely-defined locations are parts of a more coarsely define location. For example, 123 Main St Suite 400 is a part of the building at 123 Main St. Note that this construct is meant to be traversable in either direction. For example, 123 Main St Suite 400 is a part-of 123 Main St, while 123 Main St is composed-of the various suites within the building.