19. The versioned relational database system set forth in claim 7 wherein: an operation that operates on a workspace that belongs to a multi-parent graph or on a version in such a workspace and that may result in a constraint violation uses the multi-parent graph to determine whether the operation will violate the constraint.
19. The versioned relational database system set forth in claim 7 wherein: an operation that operates on a workspace that belongs to a multi-parent graph or on a version in such a workspace and that may result in a constraint violation uses the multi-parent graph to determine whether the operation will violate the constraint. 20. The versioned relational database system set forth in claim 19 wherein: the constraint is a primary key constraint, the primary key constraint being violated when the operation results in a split of a record in current versions in workspaces belonging to the multi-parent graph.