“…, R k , we use their Cartesian product R 1 × · · · × R k . For example, if we have R 1 = //employee list and R 2 = //employee/name, their instances for the XML data in Figure 6 are R 1 = {(2)} and R 2 = {(4, 6), (7,9), (11,13)}. Consequently, the instance of their Cartesian product R 1 × R 2 is: (2,7,9), (2, 11, 13)}.…”