4. The method of claim 3 , wherein generating the child language model for each of the obtained groups comprises generating a unigram language model for each of the obtained groups.
3. The method of claim 2 , wherein automatically evaluating the first metadata attribute comprises: dividing the training data instances, based on their respective values for the first metadata attribute, to obtain two or more groups of training data instances; generating a child language model for each of the obtained groups of training data instances; generating a parent language model using all the training data instances; and calculating a score for the first metadata attribute based at least in part how a measure of the goodness of fit of the generated child language models compares with a measure of the goodness of fit of the generated parent language model.