24 Search Results for "Amsterdamer, Yael"

Volume

LIPIcs, Volume 98

21st International Conference on Database Theory (ICDT 2018)

ICDT 2018, March 26-29, 2018, Vienna, Austria

Editors: Benny Kimelfeld and Yael Amsterdamer

Document
Complete Volume
DOI: 10.4230/LIPIcs.ICDT.2018
LIPIcs, Volume 98, ICDT'18, Complete Volume

Authors: Benny Kimelfeld and Yael Amsterdamer

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
LIPIcs, Volume 98, ICDT'18, Complete Volume
Cite as

21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Proceedings{kimelfeld_et_al:LIPIcs.ICDT.2018,
  title =	{{LIPIcs, Volume 98, ICDT'18, Complete Volume}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018},
  URN =		{urn:nbn:de:0030-drops-86795},
  doi =		{10.4230/LIPIcs.ICDT.2018},
  annote =	{Keywords: Information systems, Data management systems, Information systems, Database design and models, Information systems, Database query processing}
}
Document
Front Matter
DOI: 10.4230/LIPIcs.ICDT.2018.0
Front Matter, Table of Contents, Preface, Conference Organization

Authors: Benny Kimelfeld and Yael Amsterdamer

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as

21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 0:i-0:xvi, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{kimelfeld_et_al:LIPIcs.ICDT.2018.0,
  author =	{Kimelfeld, Benny and Amsterdamer, Yael},
  title =	{{Front Matter, Table of Contents, Preface, Conference Organization}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{0:i--0:xvi},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.0},
  URN =		{urn:nbn:de:0030-drops-85938},
  doi =		{10.4230/LIPIcs.ICDT.2018.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.1
Fine-grained Algorithms and Complexity

Authors: Virginia Vassilevska Williams

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
A central goal of algorithmic research is to determine how fast computational problems can be solved in the worst case. Theorems from complexity theory state that there are problems that, on inputs of size n, can be solved in t(n) time but not in O(t(n)^{1-epsilon}) time for epsilon>0. The main challenge is to determine where in this hierarchy various natural and important problems lie. Throughout the years, many ingenious algorithmic techniques have been developed and applied to obtain blazingly fast algorithms for many problems. Nevertheless, for many other central problems, the best known running times are essentially those of their classical algorithms from the 1950s and 1960s. Unconditional lower bounds seem very difficult to obtain, and so practically all known time lower bounds are conditional. For years, the main tool for proving hardness of computational problems have been NP-hardness reductions, basing hardness on P neq NP. However, when we care about the exact running time (as opposed to merely polynomial vs non-polynomial), NP-hardness is not applicable, especially if the problem is already solvable in polynomial time. In recent years, a new theory has been developed, based on "fine-grained reductions" that focus on exact running times. Mimicking NP-hardness, the approach is to (1) select a key problem X that is conjectured to require essentially t(n) time for some t, and (2) reduce X in a fine-grained way to many important problems. This approach has led to the discovery of many meaningful relationships between problems, and even sometimes to equivalence classes. The main key problems used to base hardness on have been: the 3SUM problem, the CNF-SAT problem (based on the Strong Exponential Time Hypothesis (SETH)) and the All Pairs Shortest Paths Problem. Research on SETH-based lower bounds has flourished in particular in recent years showing that the classical algorithms are optimal for problems such as Approximate Diameter, Edit Distance, Frechet Distance, Longest Common Subsequence etc. In this talk I will give an overview of the current progress in this area of study, and will highlight some exciting new developments and their relationship to database theory.
Cite as

Virginia Vassilevska Williams. Fine-grained Algorithms and Complexity. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{vassilevskawilliams:LIPIcs.ICDT.2018.1,
  author =	{Vassilevska Williams, Virginia},
  title =	{{Fine-grained Algorithms and Complexity}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{1:1--1:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.1},
  URN =		{urn:nbn:de:0030-drops-86135},
  doi =		{10.4230/LIPIcs.ICDT.2018.1},
  annote =	{Keywords: algorithms, complexity, fine-grained}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.2
Join Algorithms: From External Memory to the BSP

Authors: Ke Yi

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
Database systems have been traditionally disk-based, which had motivated the extensive study on external memory (EM) algorithms. However, as RAMs continue to get larger and cheaper, modern distributed data systems are increasingly adopting a main memory based, shared-nothing architecture, exemplified by systems like Spark and Flink. These systems can be abstracted by the BSP model (with variants like the MPC model and the MapReduce model), and there has been a strong revived interest in designing BSP algorithms for handling large amounts of data. With hard disks starting to fade away from the picture, EM algorithms may now seem less relevant. However, we observe that many of the recently developed join algorithms under the BSP model have a high degree of resemblance with their counterparts in the EM model. In this talk, I will present some recent results on join algorithms in the EM and BSP model, examine their relationships, and discuss a general theoretical framework for converting EM algorithms to the BSP.
Cite as

Ke Yi. Join Algorithms: From External Memory to the BSP. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{yi:LIPIcs.ICDT.2018.2,
  author =	{Yi, Ke},
  title =	{{Join Algorithms: From External Memory to the BSP}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{2:1--2:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.2},
  URN =		{urn:nbn:de:0030-drops-86126},
  doi =		{10.4230/LIPIcs.ICDT.2018.2},
  annote =	{Keywords: External memory model, BSP, join algorithms}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.3
An Update on Dynamic Complexity Theory

Authors: Thomas Zeume

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
In many modern data management scenarios, data is subject to frequent changes. In order to avoid costly re-computing query answers from scratch after each small update, one can try to use auxiliary relations that have been computed before. Of course, the auxiliary relations need to be updated dynamically whenever the data changes. Dynamic complexity theory studies which queries and auxiliary relations can be updated in a highly parallel fashion, that is, by constant-depth circuits or, equivalently, by first-order formulas or the relational algebra. After gently introducing dynamic complexity theory, I will discuss recent results of the area with a focus on the dynamic complexity of the reachability query.
Cite as

Thomas Zeume. An Update on Dynamic Complexity Theory. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, p. 3:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{zeume:LIPIcs.ICDT.2018.3,
  author =	{Zeume, Thomas},
  title =	{{An Update on Dynamic Complexity Theory}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{3:1--3:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.3},
  URN =		{urn:nbn:de:0030-drops-86117},
  doi =		{10.4230/LIPIcs.ICDT.2018.3},
  annote =	{Keywords: Dynamic descriptive complexity, SQL updates, Reachability}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.4
Rewriting Guarded Existential Rules into Small Datalog Programs

Authors: Shqiponja Ahmetaj, Magdalena Ortiz, and Mantas Simkus

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
The goal of this paper is to understand the relative expressiveness of the query language in which queries are specified by a set of guarded (disjunctive) tuple-generating dependencies (TGDs) and an output (or 'answer') predicate. Our main result is to show that every such query can be translated into a polynomially-sized (disjunctive) Datalog program if the maximal number of variables in the (disjunctive) TGDs is bounded by a constant. To overcome the challenge that Datalog has no direct means to express the existential quantification present in TGDs, we define a two-player game that characterizes the satisfaction of the dependencies, and design a Datalog query that can decide the existence of a winning strategy for the game. For guarded disjunctive TGDs, we can obtain Datalog rules with disjunction in the heads. However, the use of disjunction is limited, and the resulting rules fall into a fragment that can be evaluated in deterministic single exponential time. We proceed quite differently for the case when the TGDs are not disjunctive and we show that we can obtain a plain Datalog query. Notably, unlike previous translations for related fragments, our translation requires only polynomial time if the maximal number of variables in the (disjunctive) TGDs is bounded by a constant.
Cite as

Shqiponja Ahmetaj, Magdalena Ortiz, and Mantas Simkus. Rewriting Guarded Existential Rules into Small Datalog Programs. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 4:1-4:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{ahmetaj_et_al:LIPIcs.ICDT.2018.4,
  author =	{Ahmetaj, Shqiponja and Ortiz, Magdalena and Simkus, Mantas},
  title =	{{Rewriting Guarded Existential Rules into Small Datalog Programs}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{4:1--4:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.4},
  URN =		{urn:nbn:de:0030-drops-85950},
  doi =		{10.4230/LIPIcs.ICDT.2018.4},
  annote =	{Keywords: Existential rules, Expressiveness, Descriptive Complexity, Query Rewriting}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.5
Enumeration on Trees under Relabelings

Authors: Antoine Amarilli, Pierre Bourhis, and Stefan Mengel

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
We study how to evaluate MSO queries with free variables on trees, within the framework of enumeration algorithms. Previous work has shown how to enumerate answers with linear-time preprocessing and delay linear in the size of each output, i.e., constant-delay for free first-order variables. We extend this result to support relabelings, a restricted kind of update operations on trees which allows us to change the node labels. Our main result shows that we can enumerate the answers of MSO queries on trees with linear-time preprocessing and delay linear in each answer, while supporting node relabelings in logarithmic time. To prove this, we reuse the circuit-based enumeration structure from our earlier work, and develop techniques to maintain its index under node relabelings. We also show how enumeration under relabelings can be applied to evaluate practical query languages, such as aggregate, group-by, and parameterized queries.
Cite as

Antoine Amarilli, Pierre Bourhis, and Stefan Mengel. Enumeration on Trees under Relabelings. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 5:1-5:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{amarilli_et_al:LIPIcs.ICDT.2018.5,
  author =	{Amarilli, Antoine and Bourhis, Pierre and Mengel, Stefan},
  title =	{{Enumeration on Trees under Relabelings}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{5:1--5:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.5},
  URN =		{urn:nbn:de:0030-drops-86060},
  doi =		{10.4230/LIPIcs.ICDT.2018.5},
  annote =	{Keywords: enumeration, trees, updates, MSO, circuits, knowledge compilation}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.6
Connecting Width and Structure in Knowledge Compilation

Authors: Antoine Amarilli, Mikaël Monet, and Pierre Senellart

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
Several query evaluation tasks can be done via knowledge compilation: the query result is compiled as a lineage circuit from which the answer can be determined. For such tasks, it is important to leverage some width parameters of the circuit, such as bounded treewidth or pathwidth, to convert the circuit to structured classes, e.g., deterministic structured NNFs (d-SDNNFs) or OBDDs. In this work, we show how to connect the width of circuits to the size of their structured representation, through upper and lower bounds. For the upper bound, we show how bounded-treewidth circuits can be converted to a d-SDNNF, in time linear in the circuit size. Our bound, unlike existing results, is constructive and only singly exponential in the treewidth. We show a related lower bound on monotone DNF or CNF formulas, assuming a constant bound on the arity (size of clauses) and degree (number of occurrences of each variable). Specifically, any d-SDNNF (resp., SDNNF) for such a DNF (resp., CNF) must be of exponential size in its treewidth; and the same holds for pathwidth when compiling to OBDDs. Our lower bounds, in contrast with most previous work, apply to any formula of this class, not just a well-chosen family. Hence, for our language of DNF and CNF, pathwidth and treewidth respectively characterize the efficiency of compiling to OBDDs and (d-)SDNNFs, that is, compilation is singly exponential in the width parameter. We conclude by applying our lower bound results to the task of query evaluation.
Cite as

Antoine Amarilli, Mikaël Monet, and Pierre Senellart. Connecting Width and Structure in Knowledge Compilation. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 6:1-6:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{amarilli_et_al:LIPIcs.ICDT.2018.6,
  author =	{Amarilli, Antoine and Monet, Mika\"{e}l and Senellart, Pierre},
  title =	{{Connecting Width and Structure in Knowledge Compilation}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{6:1--6:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.6},
  URN =		{urn:nbn:de:0030-drops-86083},
  doi =		{10.4230/LIPIcs.ICDT.2018.6},
  annote =	{Keywords: knowledge compilation, probabilistic databases, treewidth, circuits}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.7
A More General Theory of Static Approximations for Conjunctive Queries

Authors: Pablo Barceló, Miguel Romero, and Thomas Zeume

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
Conjunctive query (CQ) evaluation is NP-complete, but becomes tractable for fragments of bounded hypertreewidth. If a CQ is hard to evaluate, it is thus useful to evaluate an approximation of it in such fragments. While underapproximations (i.e., those that return correct answers only) are well-understood, the dual notion of overapproximations that return complete (but not necessarily sound) answers, and also a more general notion of approximation based on the symmetric difference of query results, are almost unexplored. In fact, the decidability of the basic problems of evaluation, identification, and existence of those approximations, is open. We develop a connection with existential pebble game tools that allows the systematic study of such problems. In particular, we show that the evaluation and identification of overapproximations can be solved in polynomial time. We also make progress in the problem of existence of overapproximations, showing it to be decidable in 2EXPTIME over the class of acyclic CQs. Furthermore, we look at when overapproximations do not exist, suggesting that this can be alleviated by using a more liberal notion of overapproximation. We also show how to extend our tools to study symmetric difference approximations. We observe that such approximations properly extend under- and over-approximations, settle the complexity of its associated identification problem, and provide several results on existence and evaluation.
Cite as

Pablo Barceló, Miguel Romero, and Thomas Zeume. A More General Theory of Static Approximations for Conjunctive Queries. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 7:1-7:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{barcelo_et_al:LIPIcs.ICDT.2018.7,
  author =	{Barcel\'{o}, Pablo and Romero, Miguel and Zeume, Thomas},
  title =	{{A More General Theory of Static Approximations for Conjunctive Queries}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{7:1--7:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.7},
  URN =		{urn:nbn:de:0030-drops-86021},
  doi =		{10.4230/LIPIcs.ICDT.2018.7},
  annote =	{Keywords: conjunctive queries, hypertreewidth, approximations, pebble games}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.8
Answering UCQs under Updates and in the Presence of Integrity Constraints

Authors: Christoph Berkholz, Jens Keppeler, and Nicole Schweikardt

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
We investigate the query evaluation problem for fixed queries over fully dynamic databases where tuples can be inserted or deleted. The task is to design a dynamic data structure that can immediately report the new result of a fixed query after every database update. We consider unions of conjunctive queries (UCQs) and focus on the query evaluation tasks testing (decide whether an input tuple belongs to the query result), enumeration (enumerate, without repetition, all tuples in the query result), and counting (output the number of tuples in the query result). We identify three increasingly restrictive classes of UCQs which we call t-hierarchical, q-hierarchical, and exhaustively q-hierarchical UCQs. Our main results provide the following dichotomies: If the query's homomorphic core is t-hierarchical (q-hierarchical, exhaustively q-hierarchical), then the testing (enumeration, counting) problem can be solved with constant update time and constant testing time (delay, counting time). Otherwise, it cannot be solved with sublinear update time and sublinear testing time (delay, counting time), unless the OV-conjecture and/or the OMv-conjecture fails. We also study the complexity of query evaluation in the dynamic setting in the presence of integrity constraints, and we obtain similar dichotomy results for the special case of small domain constraints (i.e., constraints which state that all values in a particular column of a relation belong to a fixed domain of constant size).
Cite as

Christoph Berkholz, Jens Keppeler, and Nicole Schweikardt. Answering UCQs under Updates and in the Presence of Integrity Constraints. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 8:1-8:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{berkholz_et_al:LIPIcs.ICDT.2018.8,
  author =	{Berkholz, Christoph and Keppeler, Jens and Schweikardt, Nicole},
  title =	{{Answering UCQs under Updates and in the Presence of Integrity Constraints}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{8:1--8:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.8},
  URN =		{urn:nbn:de:0030-drops-85990},
  doi =		{10.4230/LIPIcs.ICDT.2018.8},
  annote =	{Keywords: dynamic query evaluation, union of conjunctive queries, constant-delay enumeration, counting problem, testing}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.9
Expressivity and Complexity of MongoDB Queries

Authors: Elena Botoeva, Diego Calvanese, Benjamin Cogrel, and Guohui Xiao

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
In this paper, we consider MongoDB, a widely adopted but not formally understood database system managing JSON documents and equipped with a powerful query mechanism, called the aggregation framework. We provide a clean formal abstraction of this query language, which we call MQuery. We study the expressivity of MQuery, showing the equivalence of its well-typed fragment with nested relational algebra. We further investigate the computational complexity of significant fragments of it, obtaining several (tight) bounds in combined complexity, which range from LogSpace to alternating exponential-time with a polynomial number of alternations.
Cite as

Elena Botoeva, Diego Calvanese, Benjamin Cogrel, and Guohui Xiao. Expressivity and Complexity of MongoDB Queries. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 9:1-9:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{botoeva_et_al:LIPIcs.ICDT.2018.9,
  author =	{Botoeva, Elena and Calvanese, Diego and Cogrel, Benjamin and Xiao, Guohui},
  title =	{{Expressivity and Complexity of MongoDB Queries}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{9:1--9:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.9},
  URN =		{urn:nbn:de:0030-drops-86074},
  doi =		{10.4230/LIPIcs.ICDT.2018.9},
  annote =	{Keywords: MongoDB, NoSQL, aggregation framework, expressivity}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.10
On the Expressive Power of Query Languages for Matrices

Authors: Robert Brijder, Floris Geerts, Jan Van den Bussche, and Timmy Weerwag

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
We investigate the expressive power of MATLANG, a formal language for matrix manipulation based on common matrix operations and linear algebra. The language can be extended with the operation inv of inverting a matrix. In MATLANG + inv we can compute the transitive closure of directed graphs, whereas we show that this is not possible without inversion. Indeed we show that the basic language can be simulated in the relational algebra with arithmetic operations, grouping, and summation. We also consider an operation eigen for diagonalizing a matrix, which is defined so that different eigenvectors returned for a same eigenvalue are orthogonal. We show that inv can be expressed in MATLANG + eigen. We put forward the open question whether there are boolean queries about matrices, or generic queries about graphs, expressible in MATLANG + eigen but not in MATLANG + inv. The evaluation problem for MATLANG + eigen is shown to be complete for the complexity class Exists R.
Cite as

Robert Brijder, Floris Geerts, Jan Van den Bussche, and Timmy Weerwag. On the Expressive Power of Query Languages for Matrices. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 10:1-10:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

Copy BibTex To Clipboard

@InProceedings{brijder_et_al:LIPIcs.ICDT.2018.10,
  author =	{Brijder, Robert and Geerts, Floris and Van den Bussche, Jan and Weerwag, Timmy},
  title =	{{On the Expressive Power of Query Languages for Matrices}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{10:1--10:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.10},
  URN =		{urn:nbn:de:0030-drops-86007},
  doi =		{10.4230/LIPIcs.ICDT.2018.10},
  annote =	{Keywords: matrix query languages, relational algebra with aggregates, query evaluation problem, graph queries}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.11
Enumeration Complexity of Conjunctive Queries with Functional Dependencies

Authors: Nofar Carmeli and Markus Kröll

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
We study the complexity of enumerating the answers of Conjunctive Queries (CQs) in the presence of Functional Dependencies (FDs). Our focus is on the ability to list output tuples with a constant delay in between, following a linear-time preprocessing. A known dichotomy classifies the acyclic self-join-free CQs into those that admit such enumeration, and those that do not. However, this classification no longer holds in the common case where the database exhibits dependencies among attributes. That is, some queries that are classified as hard are in fact tractable if dependencies are accounted for. We establish a generalization of the dichotomy to accommodate FDs; hence, our classification determines which combination of a CQ and a set of FDs admits constant-delay enumeration with a linear-time preprocessing. In addition, we generalize a hardness result for cyclic CQs to accommodate a common type of FDs. Further conclusions of our development include a dichotomy for enumeration with linear delay, and a dichotomy for CQs with disequalities. Finally, we show that all our results apply to the known class of "cardinality dependencies" that generalize FDs (e.g., by stating an upper bound on the number of genres per movies, or friends per person).
Cite as

Nofar Carmeli and Markus Kröll. Enumeration Complexity of Conjunctive Queries with Functional Dependencies. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 11:1-11:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{carmeli_et_al:LIPIcs.ICDT.2018.11,
  author =	{Carmeli, Nofar and Kr\"{o}ll, Markus},
  title =	{{Enumeration Complexity of Conjunctive Queries with Functional Dependencies}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{11:1--11:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.11},
  URN =		{urn:nbn:de:0030-drops-85988},
  doi =		{10.4230/LIPIcs.ICDT.2018.11},
  annote =	{Keywords: Enumeration, Complexity, CQs}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.12
Preserving Constraints with the Stable Chase

Authors: David Carral, Markus Krötzsch, Maximilian Marx, Ana Ozaki, and Sebastian Rudolph

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
Conjunctive query answering over databases with constraints – also known as (tuple-generating) dependencies – is considered a central database task. To this end, several versions of a construction called chase have been described. Given a set Sigma of dependencies, it is interesting to ask which constraints not contained in Sigma that are initially satisfied in a given database instance are preserved when computing a chase over Sigma. Such constraints are an example for the more general class of incidental constraints, which when added to Sigma as new dependencies do not affect certain answers and might even speed up query answering. After formally introducing incidental constraints, we show that deciding incidentality is undecidable for tuple-generating dependencies, even in cases for which query entailment is decidable. For dependency sets with a finite universal model, the core chase can be used to decide incidentality. For the infinite case, we propose the stable chase, which generalises the core chase, and study its relation to incidental constraints.
Cite as

David Carral, Markus Krötzsch, Maximilian Marx, Ana Ozaki, and Sebastian Rudolph. Preserving Constraints with the Stable Chase. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 12:1-12:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

Copy BibTex To Clipboard

@InProceedings{carral_et_al:LIPIcs.ICDT.2018.12,
  author =	{Carral, David and Kr\"{o}tzsch, Markus and Marx, Maximilian and Ozaki, Ana and Rudolph, Sebastian},
  title =	{{Preserving Constraints with the Stable Chase}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{12:1--12:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.12},
  URN =		{urn:nbn:de:0030-drops-86015},
  doi =		{10.4230/LIPIcs.ICDT.2018.12},
  annote =	{Keywords: Incidental constraints, Tuple-generating dependencies, Infinite core chase, Universal Model, BCQ entailment}
}
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