O. Balovnev, M. Breunig, и A. Cremers. Advances in Spatial Databases, том 1262 из Lecture Notes in Computer Science, Springer, Berlin / Heidelberg, (1997)
M. Trzaska, и K. Subieta. Proc. of the Eighth East-European Conference on Advances in Databases and Information Systems (ADBIS'2004, стр. 228--240. (2004)