4. The method as claimed in claim 3 wherein step (d) comprises applying a grouping function g to the set of contexts to combine the contexts into a smaller set of contexts.
4. The method as claimed in claim 3 wherein step (d) comprises applying a grouping function g to the set of contexts to combine the contexts into a smaller set of contexts. 8. The method as claimed in claim 4 wherein said step of applying a grouping function g comprises: i. creating groupings of contexts from said initial set of contexts ii. calculating a conditional entropy for each grouping of contexts iii. selecting a reduced number of groupings based on said calculated conditional entropy; and iv. reducing a size of said initial set of contexts by replacing elements which comprise the selected groupings with said groupings.