Leonid Libkin. Incomplete information and certain answers in general data models. In Maurizio Lenzerini, Thomas Schwentick, editors, Proceedings of the 30th ACM SIGMOD-SIGACT-SIGART Symposium on Principles of Database Systems, PODS 2011, June 12-16, 2011, Athens, Greece. pages 59-70, ACM, 2011. [doi]
Abstract is missing.