21. The computer-readable non-transitory storage medium of claim 20 , wherein the SQL statement selects data only from the particular column of the particular relational table.
21. The computer-readable non-transitory storage medium of claim 20 , wherein the SQL statement selects data only from the particular column of the particular relational table. 24. The computer-readable non-transitory storage medium of claim 21 , further comprising instructions to perform a step of performing operations on the target data after retrieving the target data, wherein the operations on the target data are performed by the relational database system receiving a second Xpath expression and converting the second Xpath expression into a second SQL statement.