In this discussion, there has been reference to the use of the Decorator pattern from the Gang of Four book and its use as an alternative for Generalization.  There are really two separate issues here.  One is what the intended use is of the Decorator pattern as expressed in the book and the other is whether or not the usage in Model-Set-Entty which Phil describes by reference to Decorator is or is not the preferred way of dealing with subtypes in the context of M-S-E.   I felt this was a discussion which needed more detail than would work in an on-line forum, so I have written a whitepaper to present my views on Decorator as given by GoF.  This can be found here .  The discussion about Model-Set-Entity in general will be forthcoming later.  I am hoping that Phil will write up his own views on Decorator and publish them.  When he does, I will link from mine to his since I think this exchange of viewpoints has educational value.