The language supports the usual comparators (=, <, in, like, etc.), logical operators (and, or, not), and bag functions (count, sum, etc.), as well as a modal operator (possibly) for conceptual left outer joins. Subtype/supertype connections appear as “is” predicates. For example,...
Pedreschi. Composing Operators for Logic Theories. In J. W. Lloyd, editor, Computational Logic, pages 117–134. Springer-Verlag, Berlin, 1990. Google Scholar A. D. Burt, P. M. Hill, and J. W. Lloyd. Preliminary Report on the Logic Programming Language Gödel. Technical Report TR 90...
The query language is a conservative extension of relational algebra where special operators allow the specification of queries over contexts.doi:10.1007/978-3-7908-2404-9_25Davide MartinenghiRiccardo TorloneD. Martinenghi, R. Torlone, A logical approach to context-aware databases, Springer, 2010....