Correctness of SQL Queries on Databases with Nulls

Guagliardo, Paolo; Libkin, Leonid

doi:10.1145/3156655.3156657

Cited by 15 publications

(17 citation statements)

References 30 publications

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“…It is thus natural to define certainty based on a greatest-lowerbound operation (GLB) for semiring annotations based on so-called l-semirings [33] where the GLB is well behaved. We show that certain annotations correspond to the classical notion of certain answers for set [39] and bag [26] semantics. UA-DBs.…”

Section: Introductionmentioning

confidence: 89%

“…Certain Answers. Many approaches for answering queries over incomplete databases employ certain answer semantics [2,[25][26][27]38]. The foundational work by Lipski [39] defined certain answers analogously to our approach, but using minima instead of GLBs.…”

Section: Related Workmentioning

confidence: 99%

“…Reiter [42] proposed a PTIME algorithm that returns a subset of the certain answers (c-sound) for positive existential queries (and a limited form of universal queries). Guagliardo and Libkin [25,26,38] propose a query semantics that preserves c-soundness for full relational algebra (first order queries) for Codd-and Vtables. Then, [26] defined certain and possible multiplicities for bag semantics, and presented initial thoughts on how to extend [25] for bag semantics.…”

Section: Related Workmentioning

confidence: 99%

“…Then, [26] defined certain and possible multiplicities for bag semantics, and presented initial thoughts on how to extend [25] for bag semantics. Our approach works with a wider range of data models and models of uncertainty than [25,26], at the cost of being a slightly weaker approximation. Furthermore, unlike this approach, UA-DBs are closed under query evaluation.…”

Section: Related Workmentioning

confidence: 99%

“…This addresses the performance problem, but under-approximations only exacerbate the problem of excluded results. Worse, these techniques are limited to specific uncertain data models such as V-tables, and with the exception of a brief discussion in [26], only support set semantics. x-table [3], a type of incomplete data model where each tuple may have multiple alternatives.…”

Section: Introductionmentioning

confidence: 99%

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Uncertainty Annotated Databases - A Lightweight Approach for Approximating Certain Answers

Huber

Glavic

et al. 2019

Proceedings of the 2019 International Conference on Management of Data

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Certain answers are a principled method for coping with uncertainty that arises in many practical data management tasks. Unfortunately, this method is expensive and may exclude useful (if uncertain) answers. Thus, users frequently resort to less principled approaches to resolve the uncertainty. In this paper, we propose Uncertainty Annotated Databases (UA-DBs), which combine an under-and over-approximation of certain answers to achieve the reliability of certain answers, with the performance of a classical database system. Furthermore, in contrast to prior work on certain answers, UA-DBs achieve a higher utility by including some (explicitly marked) answers that are not certain. UA-DBs are based on incomplete K-relations, which we introduce to generalize the classical set-based notions of incomplete databases and certain answers to a much larger class of data models. Using an implementation of our approach, we demonstrate experimentally that it efficiently produces tight approximations of certain answers that are of high utility.

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Section: Introductionmentioning

confidence: 89%