Department of Computer Science, Georgia State University, 34 Peachtree Street, Atlanta, USA. yipan@gsu.edu.|Department of Computer Science, Georgia State University, 34 Peachtree Street, Atlanta, USA. yipan@gsu.edu.|Department of Computer Science, Georgia State University, 34 Peachtree Street, Atlanta, USA. yipan@gsu.edu.|Dipartimento di Ingegneria e Scienza dellInformazione, University of Trento, Trento, Italy. passerini@disi.unitn.it.