“…Although they can be handcrafted [15,24,4,42,51,50,20], the costs involved motivated many researchers to work on proposals to learn them automatically. These proposals are either supervised, i.e., they require the user to provide a number of information samples to be extracted [11,44,58,26,32,8,22,9,14,18,30,5,40,21,59], or unsupervised, i.e., they extract as much prospective information as they can and the user then gathers the relevant information from the results [62,12,16,2,28,25,60,39,46,64,67,38,59,57].…”