Or perhaps go the more novel way of Piumarta's and Warth's Open, extensible object models? http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.6603&rep

Or perhaps go the more novel way of Piumarta's and Warth's Open, extensible object models? http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121.6603&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.121...