Raimondo Schettini Carla Brambilla Gianluigi Ciocca Anna Valsasna Mauro De Ponti A hierarchical classification strategy for digital documents. 1759-1769 2002 35 Pattern Recognition 8 http://dx.doi.org/10.1016/S0031-3203(01)00168-6 db/journals/pr/pr35.html#SchettiniBCVP02