Ali Enayat had asked whether two halves of Disjunctive Correctness (DC) for the compositional truth predicate are conservative over Peano Arithmetic (PA). In this paper, we show that principle “every true disjunction has a disjunct” is equivalent to bounded induction and thus it not conservative. On other hand, converse implication “any with disjunct true” can be conservatively added PA. The me...

We examine the query planning problem in information integration systems in the presence of sources that contain disjunctive information. We show that datalog, the language of choice for representing query plans in information integration systems, is not sufficiently expressive in this case. We prove that disjunctive datalog with inequality is sufficiently expressive, and present a construction...