Consistent Query Answering for Primary Keys on Path Queries

Koutris, Paraschos; Ouyang, Xiating; Wijsen, Jef

doi:10.1145/3452021.3458334

Cited by 7 publications

(3 citation statements)

References 51 publications

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“…By Corollary 22, r must contain an R-fact (call it B) of block(θ(R), db). Then B ∈ r 0 ∩ db 0 , and by (13), B ∈ r * 0 . Since r * 0 is consistent with respect to primary keys, we obtain θ(R) = B, and hence θ(R) ∈ r 0 , a contradiction.…”

Section: It Suffices To Show the Followingmentioning

confidence: 96%

“…For self-join-free conjunctive queries with respect to multiple keys, it remains decidable whether or not CERTAINTY(q) is in FO [12]. The complexity landscape of CERTAINTY(q) for path queries, a subclass of (not necessarily self-join-free) conjunctive queries, was settled in [13]. For unions of conjunctive queries q, Fontaine [14] established interesting relationships between CERTAINTY(q) and Bulatov's dichotomy theorem for conservative CSP [15].…”

Section: Related Workmentioning

confidence: 99%

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A Dichotomy in Consistent Query Answering for Primary Keys and Unary Foreign Keys

Hannula¹,

Wijsen²

2022

Preprint

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Since 2005, significant progress has been made in the problem of Consistent Query Answering (CQA) with respect to primary keys. In this problem, the input is a database instance that may violate one or more primary key constraints. A repair is defined as a maximal subinstance that satisfies all primary keys. Given a Boolean query q, the question then is whether q holds true in every repair. So far, theoretical research in this field has not addressed the combination of primary key and foreign key constraints, despite the importance of referential integrity in database systems. This paper addresses the problem of CQA with respect to both primary keys and foreign keys. In this setting, it is natural to adopt the notion of symmetric-difference repairs, because foreign keys can be repaired by inserting new tuples. We consider the case where foreign keys are unary, and queries are conjunctive queries without self-joins. In this setting, we characterize the boundary between those CQA problems that admit a consistent first-order rewriting, and those that do not. Keywords consistent query answering • primary key • foreign key • conjunctive query 1 IntroductionConsistent query answering (CQA) was introduced in [1] as a principled semantics for answering queries on inconsistent databases. A symmetric-difference repair (or ⊕-repair) of a database db is defined as a consistent database r that ⊆-minimizes the symmetric difference with db. Informally, a ⊕-repair r becomes inconsistent as soon as we insert into it more tuples of db, or delete from it tuples not in db. Then, given a query q( x), an answer a is called consistent if q( a) holds true in every repair. The problem is often studied for Boolean queries q, where the question is to determine whether q holds true on every repair of a given input database.CQA has been studied in depth in case that the only constraints are primary keys, one per relation. In [2], this problem was coined as CERTAINTY(q), in which notation it is understood that every relation name in q has a predefined primary key. More than a decade of research has eventually resulted in the following complexity classification [3]: for every self-join-free Boolean conjunctive query q, the problem CERTAINTY(q) is either in FO, L-complete, or coNP-complete. Now that this classification has been settled, it is natural to ask what happens if we add foreign key constraints. Indeed, every relational database textbook is likely to introduce very soon the notion of referential integrity, i.e., foreign keys referencing primary keys. In view thereof, one may even wonder why referential integrity in CQA has so far received little theoretical research attention. One plausible explanation is that ⊕-repairs with respect to primary keys are easy to characterize: every repair has to delete, in every block, all tuples but one, where a block is a maximal set of tuples of the same relation that agree on their primary key. In contrast, ⊕-repairs with respect to foreign keys can introduce new tuples, as illustrated next. It will ...

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Section: It Suffices To Show the Followingmentioning

confidence: 96%

Section: Related Workmentioning

confidence: 99%

A Dichotomy in Consistent Query Answering for Primary Keys and Unary Foreign Keys

Hannula¹,

Wijsen²

2022

Preprint

Self Cite

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show abstract

“…In the literature on CQA, the schema constraints considered are (subclasses of) tuplegenerating dependencies (TGDs), equality-generating dependencies (EGDs), and universal constraints [10,13,4,21,12]. The schema constraints that we consider in this paper are a very large class of database dependencies that captures and generalizes all the above classes of constraints, and correspond to the class of disjunctive embedded dependencies with inequalities (DEDs) [9,8].…”

Section: Introductionmentioning

confidence: 99%

Consistent Query Answering for Expressive Constraints under Tuple-Deletion Semantics

Marconi¹,

Rosati²

2022

Preprint

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We study consistent query answering in relational databases. We consider an expressive class of schema constraints that generalizes both tuple-generating dependencies and equalitygenerating dependencies. We establish the complexity of consistent query answering and repair checking under tuple-deletion semantics for different fragments of the above constraint language. In particular, we identify new subclasses of constraints in which the above problems are tractable or even first-order rewritable.

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Benchmarking Approximate Consistent Query Answering

Console

Pieris

2021

Proceedings of the 40th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems

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Consistent query answering (CQA) aims to deliver meaningful answers when queries are evaluated over inconsistent databases. Such answers must be certainly true in all repairs, which are consistent databases whose difference from the inconsistent one is somehow minimal. Although CQA provides a clean framework for querying inconsistent databases, it is arguably more informative to compute the percentage of repairs in which a candidate answer is true, instead of simply saying that is true in all repairs, or is false in at least one repair. It should not be surprising, though, that computing this percentage is computationally hard. On the other hand, for practically relevant settings such as conjunctive queries and primary keys, there are data-efficient randomized approximation schemes for approximating this percentage. Our goal is to perform a thorough experimental evaluation and comparison of those approximation schemes. Our analysis provides new insights on which technique is indicated depending on key characteristics of the input.

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Consistent Query Answering for Primary Keys on Path Queries

Cited by 7 publications

References 51 publications

A Dichotomy in Consistent Query Answering for Primary Keys and Unary Foreign Keys

A Dichotomy in Consistent Query Answering for Primary Keys and Unary Foreign Keys

Consistent Query Answering for Expressive Constraints under Tuple-Deletion Semantics

Benchmarking Approximate Consistent Query Answering

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