A Journey to the Frontiers of Query Rewritability

This paper is about (first order) query rewritability in the context of theory-mediated query answering. The starting point of our journey is the FUS/FES conjecture, saying that if a theory is core-terminating (FES) and admits query rewriting (BDD, FUS) then it is uniformly bounded. We show that this conjecture is true for a wide class of "local" BDD theories. Then we ask how non-local can a BDD theory actually be and we discover phenomena which we think are quite counter-intuitive.