Every system which satisfies rules 1 through 13 deserves the OODBS label. When designing such a system, there are still a lot of design choices to be made. These are the degrees of freedom for the OODBS implementors. These characteristics differ from the mandatory ones in the sense that no consensus has yet been reached by the scientific community concerning them. They also differ from the optional features in that we do not know which of the alternatives are more or less object-oriented.