30. The system of claim 26 , wherein the feature availability computing module obtains data related to the number of headnote sentences and non headnotes for a specific feature value of each of the predetermined features.
30. The system of claim 26 , wherein the feature availability computing module obtains data related to the number of headnote sentences and non headnotes for a specific feature value of each of the predetermined features. 31. The system of claim 30 , wherein the feature graph generating module computes probability value for a specific feature value of each of the predetermined features using the obtained data.