9. The method of claim 8 wherein the approximation algorithm provides a near optimal solution to an NP-hard n-gram selection problem, the method further comprising: providing the approximation algorithm with a definable ratio bound of the optimal solution.
9. The method of claim 8 wherein the approximation algorithm provides a near optimal solution to an NP-hard n-gram selection problem, the method further comprising: providing the approximation algorithm with a definable ratio bound of the optimal solution. 10. The method of claim 9 wherein the definable ratio bound is:  C ′   C *  > 1 - 1 ⅇ where I C*I is a number of points covered by an optimum solution C* and I C′ I is a number of points covered by the near optimal solution produced by the approximation algorithm.