Insufficiency of First Order Logic as a Database Query Language

The paper explores “logic+control” programming paradigm, applied to a relational domain. Even though it looks natural to utilize first order logic as a database query language, the paper reveals some shortcomings of such an approach. Particular attention is paid to: a) the semantics of negation and other non-monotonic reasoning notions, b) infinite or time consuming recursions, c) embedded PROLOG data structures and control mechanisms. The dual interpretation of logic programs (procedural and declarative) provides a ground to study formalisms for non-monotonic reasoning. It is shown that the formal meaning of negation, which grew out of an attempt to capture commonsense reasoning, is not complete and renders some PROLOG control mechanisms unsound. Moreover, attempts to better understand negation led to mechanisms that often do not terminate due to infinite positive or negative loops.