15. The versioned relational database system set forth in claim 8 wherein: the change propagation operation is a refresh operation that propagates a change in a version in a non-leaf node in the multi-parent graph to a version in the leaf node in the multi-parent graph.
15. The versioned relational database system set forth in claim 8 wherein: the change propagation operation is a refresh operation that propagates a change in a version in a non-leaf node in the multi-parent graph to a version in the leaf node in the multi-parent graph. 16. The versioned relational database system set forth in claim 15 wherein: the refresh operation propagates the change from a version in the root node.