9. A computer program product for decomposing a decision table, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to perform a method comprising: determining that invocation criteria are met for a decision table, wherein the invocation criteria require at least one of the decision table meeting a size threshold and processing of the decision table meeting a time threshold; wherein the decision table comprises two or more columns, and wherein the two or more columns of the decision table comprise: one or more condition columns together indicating, for each row of the decision table, a condition upon which an action is to be taken; and one or more action columns together indicating, for each row of the decision table, the action to be taken given the condition specified in the one or more condition columns; decomposing, responsive to the invocation criteria being met, the decision table from a single table into a first sub-table and a second sub-table, the decomposing being based on a semantic model describing relations among the two or more columns of the decision table, and the decomposing being further based on a mapping table that maps each sub-tuple of the one or more condition columns to an assessment value, the decomposing comprising: dividing the decision table into two or more groups of rows, wherein each group of rows comprises one or more action sub-tuples representing values of the one or more action columns, and wherein the one or more action sub-tuples have equivalent values in the one or more action columns within each group of rows; selecting a first subset of condition columns from the one or more condition columns of the decision table, wherein the first subset of condition columns meets selection criteria requiring that values of the sub-tuples from a complementary subset of condition columns to the first subset of condition columns are identical within each group of rows; populating in the first sub-table the first subset of condition columns selected from the one or more condition columns of the decision table; including in the first sub-table a new action column representing a respective assessment value of each row of the first sub-table, each respective assessment value determined as a value corresponding to a respective row of the first sub-table according to the mapping table; populating in the second sub-table a second subset of condition columns from the one or more condition columns of the decision table, wherein the second set of condition columns is distinct from the first set of condition columns; including in the second sub-table a new condition column representing a respective assessment value of each row of the second sub-table, wherein the respective assessment value of each row of the second sub-table is determined based on a value of a corresponding row in the decision table as mapped by the mapping table, and wherein, in the second sub-table, the new condition column replaces the first subset of condition columns in the decision table; wherein each of the first sub-table and the second sub-table is a distinct decision table; wherein the first sub-table and the second sub-table together represent the decision table, such that a first combination of values in the condition columns maps to a first action in the decision table, the first combination of values in the first subset of condition columns maps to a corresponding assessment value in the new action column of the first sub-table, and the corresponding assessment value and the first combination of values in the second subset of condition columns map to the first action in the second sub-table; and recursively performing the decomposing on the second-table resulting from the decomposing until no subset of condition columns is identifiable as meeting the selection criteria in the second sub-table.
9. A computer program product for decomposing a decision table, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to perform a method comprising: determining that invocation criteria are met for a decision table, wherein the invocation criteria require at least one of the decision table meeting a size threshold and processing of the decision table meeting a time threshold; wherein the decision table comprises two or more columns, and wherein the two or more columns of the decision table comprise: one or more condition columns together indicating, for each row of the decision table, a condition upon which an action is to be taken; and one or more action columns together indicating, for each row of the decision table, the action to be taken given the condition specified in the one or more condition columns; decomposing, responsive to the invocation criteria being met, the decision table from a single table into a first sub-table and a second sub-table, the decomposing being based on a semantic model describing relations among the two or more columns of the decision table, and the decomposing being further based on a mapping table that maps each sub-tuple of the one or more condition columns to an assessment value, the decomposing comprising: dividing the decision table into two or more groups of rows, wherein each group of rows comprises one or more action sub-tuples representing values of the one or more action columns, and wherein the one or more action sub-tuples have equivalent values in the one or more action columns within each group of rows; selecting a first subset of condition columns from the one or more condition columns of the decision table, wherein the first subset of condition columns meets selection criteria requiring that values of the sub-tuples from a complementary subset of condition columns to the first subset of condition columns are identical within each group of rows; populating in the first sub-table the first subset of condition columns selected from the one or more condition columns of the decision table; including in the first sub-table a new action column representing a respective assessment value of each row of the first sub-table, each respective assessment value determined as a value corresponding to a respective row of the first sub-table according to the mapping table; populating in the second sub-table a second subset of condition columns from the one or more condition columns of the decision table, wherein the second set of condition columns is distinct from the first set of condition columns; including in the second sub-table a new condition column representing a respective assessment value of each row of the second sub-table, wherein the respective assessment value of each row of the second sub-table is determined based on a value of a corresponding row in the decision table as mapped by the mapping table, and wherein, in the second sub-table, the new condition column replaces the first subset of condition columns in the decision table; wherein each of the first sub-table and the second sub-table is a distinct decision table; wherein the first sub-table and the second sub-table together represent the decision table, such that a first combination of values in the condition columns maps to a first action in the decision table, the first combination of values in the first subset of condition columns maps to a corresponding assessment value in the new action column of the first sub-table, and the corresponding assessment value and the first combination of values in the second subset of condition columns map to the first action in the second sub-table; and recursively performing the decomposing on the second-table resulting from the decomposing until no subset of condition columns is identifiable as meeting the selection criteria in the second sub-table. 10. The computer program product of claim 9 , wherein the selecting the first subset of condition columns from among the one or more condition columns further comprises: identifying as the first subset of condition columns at least two of the one or more condition columns that are semantically related to one another based on the semantic model.