@Override
    public String toString() {
        return "[ " + "FROM:("
                + (source == null ? "no source" : (source.md == null ? "no source MD" : source.md.toString())) + ") "
                + "TO:(" + (target == null ? "no target" : (target.md == null ? "no target MD" : target.md.toString()))
                + ") " + "version=" + version + ", scope=" + (scope == null ? "null" : scope.getScope()) + ", depth="