A Journey to the Frontiers of Query Rewritability

TL;DR

This paper explores the boundaries of query rewritability in theory-mediated query answering, proving a conjecture for local theories and revealing surprising behaviors of non-local theories.

Contribution

It proves the FUS/FES conjecture for a broad class of local BDD theories and investigates the extent of non-locality in BDD theories, uncovering counter-intuitive phenomena.

Findings

FES and BDD imply uniform boundedness for local theories

The FUS/FES conjecture holds for a wide class of local BDD theories

Non-local BDD theories exhibit unexpected behaviors

Abstract

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.