Computing Possible and Certain Answers over Order-Incomplete Data

Abstract : This paper studies the complexity of query evaluation for databases whose relations are partially ordered; the problem commonly arises when combining ordered data from multiple sources. We focus on queries in a useful fragment of SQL, namely positive relational algebra with aggregates, whose bag semantics we extend to the partially ordered setting. Our semantics leads to the study of two main computational problems, namely the possibility and certainty of query answers. We show that these problems are respectively NP-complete and coNP-complete, but identify tractable cases depending on the query operators or input partial orders. We further introduce a duplicate elimination operator and study its effect on the complexity results.
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https://hal.inria.fr/hal-01891811
Contributor : Pierre Senellart <>
Submitted on : Wednesday, October 10, 2018 - 8:27:07 AM
Last modification on : Friday, June 7, 2019 - 11:18:38 AM

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  • HAL Id : hal-01891811, version 1
  • ARXIV : 1801.06396

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Antoine Amarilli, Mouhamadou Lamine Ba, Daniel Deutch, Pierre Senellart. Computing Possible and Certain Answers over Order-Incomplete Data. 2018. ⟨hal-01891811⟩

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