ACID: A system for computing approximate certain query answers over incomplete databases

Incomplete information arises in many current database applications. Certain answers are a widely accepted semantics of query answering over incomplete databases. Since their computation is a coNP-hard problem, recent research has focused on developing polynomial time approximation algorithms computing a sound (but possibly incomplete) set of certain answers. In this demo we showcase ACID, a system to compute sound sets of certain answers. The central tools of its underlying algorithms are conditional tables and the conditional evaluation of relation algebra. Different evaluation strategies can be applied, with more accurate ones having higher complexity, but returning more certain answers. We show how to query incomplete databases using the ACID system, which offers a suite of approximation algorithms enabling users to choose the technique that best meets their needs in terms of balance between efficiency and quality of the result's approximation.