The simplest way to associate one object with another is to include an instance of one class as a data member of the other. For instance, every piece of real_property has one and only one address. If address doesn’t need to exist outside of real_property and it doesn’t need to be specialized, then it makes sense for real_property to have a data member of type address. An RWCString attribute is handled in a comparable way, except that serialization support must also be added for address.