1. A computer program product comprising a computer readable storage medium having a computer readable program stored therein, wherein the computer readable program, when executed on a computing device, causes the computing device to: receive a natural language document comprising tabular data; analyze the tabular data within the natural language document to identify at least one portion of the tabular data comprising an erroneous or missing data value; determine, for the at least one portion, a functional dependency of the at least one portion of the tabular data on one or more other portions of the tabular data by reference to the natural language document; determine for the at least one portion, a correct data value for the erroneous or missing data value of the at least one portion of the tabular data based on the determined functional dependency of the at least one portion; modify the tabular data to replace the erroneous or missing data value with the correct data value and thereby generate a modified tabular data structure; and perform a processing operation on the modified tabular data structure to generate a resulting output.