D. Marghescu, и M. Rajanen. Proceedings of IASTED International Conference on Databases and Applications (DBA 2005), стр. 181-186. IASTED/ACTA Press, (2005)
R. Czekster, и O. de Souza. COMPUTATIONAL SCIENCE AND ITS APPLICATIONS - ICCSA 2006, PT 1, том 3980 из LECTURE NOTES IN COMPUTER SCIENCE, SPRINGER-VERLAG BERLIN, HEIDELBERGER PLATZ 3, D-14197 BERLIN, GERMANY, (2006)