Top-K oracle: A new way to present top-k tuples for uncertain data

Abstract

Managing noisy and uncertain data is needed in a great number of modern applications. A major difficulty in managing such data is the sheer number of query result tuples with diverse probabilities. In many cases, users have a preference over the tuples in a deterministic world, determined by a scoring function. Yet it has been a challenging problem to return top-k for uncertain data. Various semantics have been proposed, and they have been shown to give wildly different tuple rankings. In this paper, we propose a completely different approach. Instead of returning users fc tuples, which are merely one point in the complex distribution of top-k tuple vectors, we provide a so-called top-k oracle and users can arbitrarily query it. Intuitively, an oracle is a black box that, whenever given an SQL query, returns its result. Any information we give is based on faithful, best-effort estimates of the ground-truth top-k tuples. This is especially critical in emergency response applications and in monitoring top-k applications. Furthermore, we are the first to provide the nested query capability with the uncertain top-k result being a subquery. We devise various query processing algorithms for top-k oracles, and verify their efficiency and accuracy through a systematic evaluation over real-world and synthetic datasets.