@article {DBLP:journals/jcss/GiannottiPZ01, title = {Semantics and Expressive Power of Nondeterministic Constructs in Deductive Databases}, journal = {J. Comput. Syst. Sci.}, volume = {62}, number = {1}, year = {2001}, pages = {15-42}, author = {Fosca Giannotti and Dino Pedreschi and Carlo Zaniolo} }