Dear R Developers: I'm part of a group of people working to extend an existing object-oriented mimicing layer(R.oo) to use S4 at its base rather than S3. The existing package(S3-based) has a set of useful attributes for large scale development: pass-by-reference, common inheritance structure(root object), coding convention and others. Can anyone point me to some good resources for the difference between S3 and S4? Also, is there any really comprehensive discussion about how this S4 struct/dispatch/CLOS-like(?) way of thinking about object oriented programming differs from traditional object oriented programming?(FOP vs. OOP, in the words of Henrik Bengtsson.) Thanks a lot, Nathan Whitehouse Programmer Shaw Lab Baylor College of Medicine