6 Search Results for "Spinrath, Christopher"

Document
DOI: 10.4230/LIPIcs.MFCS.2023.80
Dynamic Constant Time Parallel Graph Algorithms with Sub-Linear Work

Authors: Jonas Schmidt and Thomas Schwentick

Published in: LIPIcs, Volume 272, 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)

Abstract
The paper proposes dynamic parallel algorithms for connectivity and bipartiteness of undirected graphs that require constant time and 𝒪(n^{1/2+ε}) work on the CRCW PRAM model. The work of these algorithms almost matches the work of the 𝒪(log n) time algorithm for connectivity by Kopelowitz et al. (2018) on the EREW PRAM model and the time of the sequential algorithm for bipartiteness by Eppstein et al. (1997). In particular, we show that the sparsification technique, which has been used in both mentioned papers, can in principle also be used for constant time algorithms in the CRCW PRAM model, despite the logarithmic depth of sparsification trees.
Cite as

Jonas Schmidt and Thomas Schwentick. Dynamic Constant Time Parallel Graph Algorithms with Sub-Linear Work. In 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 272, pp. 80:1-80:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{schmidt_et_al:LIPIcs.MFCS.2023.80,
  author =	{Schmidt, Jonas and Schwentick, Thomas},
  title =	{{Dynamic Constant Time Parallel Graph Algorithms with Sub-Linear Work}},
  booktitle =	{48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)},
  pages =	{80:1--80:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-292-1},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{272},
  editor =	{Leroux, J\'{e}r\^{o}me and Lombardy, Sylvain and Peleg, David},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2023.80},
  URN =		{urn:nbn:de:0030-drops-186140},
  doi =		{10.4230/LIPIcs.MFCS.2023.80},
  annote =	{Keywords: Dynamic parallel algorithms, Undirected connectivity, Bipartiteness}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2023.81
On the Work of Dynamic Constant-Time Parallel Algorithms for Regular Tree Languages and Context-Free Languages

Authors: Jonas Schmidt, Thomas Schwentick, and Jennifer Todtenhoefer

Published in: LIPIcs, Volume 272, 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)

Abstract
Previous work on Dynamic Complexity has established that there exist dynamic constant-time parallel algorithms for regular tree languages and context-free languages under label or symbol changes. However, these algorithms were not developed with the goal to minimise work (or, equivalently, the number of processors). In fact, their inspection yields the work bounds 𝒪(n²) and 𝒪(n⁷) per change operation, respectively. In this paper, dynamic algorithms for regular tree languages are proposed that generalise the previous algorithms in that they allow unbounded node rank and leaf insertions, while improving the work bound from 𝒪(n²) to 𝒪(n^ε), for arbitrary ε > 0. For context-free languages, algorithms with better work bounds (compared with 𝒪(n⁷)) for restricted classes are proposed: for every ε > 0 there are such algorithms for deterministic context-free languages with work bound 𝒪(n^{3+ε}) and for visibly pushdown languages with work bound 𝒪(n^{2+ε}).
Cite as

Jonas Schmidt, Thomas Schwentick, and Jennifer Todtenhoefer. On the Work of Dynamic Constant-Time Parallel Algorithms for Regular Tree Languages and Context-Free Languages. In 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 272, pp. 81:1-81:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{schmidt_et_al:LIPIcs.MFCS.2023.81,
  author =	{Schmidt, Jonas and Schwentick, Thomas and Todtenhoefer, Jennifer},
  title =	{{On the Work of Dynamic Constant-Time Parallel Algorithms for Regular Tree Languages and Context-Free Languages}},
  booktitle =	{48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)},
  pages =	{81:1--81:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-292-1},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{272},
  editor =	{Leroux, J\'{e}r\^{o}me and Lombardy, Sylvain and Peleg, David},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2023.81},
  URN =		{urn:nbn:de:0030-drops-186152},
  doi =		{10.4230/LIPIcs.MFCS.2023.81},
  annote =	{Keywords: Dynamic complexity, work, parallel constant time}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2023.16
Work-Efficient Query Evaluation with PRAMs

Authors: Jens Keppeler, Thomas Schwentick, and Christopher Spinrath

Published in: LIPIcs, Volume 255, 26th International Conference on Database Theory (ICDT 2023)

Abstract
The paper studies query evaluation in parallel constant time in the PRAM model. While it is well-known that all relational algebra queries can be evaluated in constant time on an appropriate CRCW-PRAM, this paper is interested in the efficiency of evaluation algorithms, that is, in the number of processors or, asymptotically equivalent, in the work. Naive evaluation in the parallel setting results in huge (polynomial) bounds on the work of such algorithms and in presentations of the result sets that can be extremely scattered in memory. The paper first discusses some obstacles for constant time PRAM query evaluation. It presents algorithms for relational operators that are considerably more efficient than the naive approaches. Further it explores three settings, in which efficient sequential query evaluation algorithms exist: acyclic queries, semi-join algebra queries, and join queries - the latter in the worst-case optimal framework. Under natural assumptions on the representation of the database, the work of the given algorithms matches the best sequential algorithms in the case of semi-join queries, and it comes close in the other two settings. An important tool is the compaction technique from Hagerup (1992).
Cite as

Jens Keppeler, Thomas Schwentick, and Christopher Spinrath. Work-Efficient Query Evaluation with PRAMs. In 26th International Conference on Database Theory (ICDT 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 255, pp. 16:1-16:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{keppeler_et_al:LIPIcs.ICDT.2023.16,
  author =	{Keppeler, Jens and Schwentick, Thomas and Spinrath, Christopher},
  title =	{{Work-Efficient Query Evaluation with PRAMs}},
  booktitle =	{26th International Conference on Database Theory (ICDT 2023)},
  pages =	{16:1--16:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-270-9},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{255},
  editor =	{Geerts, Floris and Vandevoort, Brecht},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2023.16},
  URN =		{urn:nbn:de:0030-drops-177589},
  doi =		{10.4230/LIPIcs.ICDT.2023.16},
  annote =	{Keywords: PRAM, query evaluation, work-efficient, parallel, acyclic queries, free-connex queries}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2022.8
Rewriting with Acyclic Queries: Mind Your Head

Authors: Gaetano Geck, Jens Keppeler, Thomas Schwentick, and Christopher Spinrath

Published in: LIPIcs, Volume 220, 25th International Conference on Database Theory (ICDT 2022)

Abstract
The paper studies the rewriting problem, that is, the decision problem whether, for a given conjunctive query Q and a set 𝒱 of views, there is a conjunctive query Q' over 𝒱 that is equivalent to Q, for cases where the query, the views, and/or the desired rewriting are acyclic or even more restricted. It shows that, if Q itself is acyclic, an acyclic rewriting exists if there is any rewriting. An analogous statement also holds for free-connex acyclic, hierarchical, and q-hierarchical queries. Regarding the complexity of the rewriting problem, the paper identifies a border between tractable and (presumably) intractable variants of the rewriting problem: for schemas of bounded arity, the acyclic rewriting problem is NP-hard, even if both Q and the views in 𝒱 are acyclic or hierarchical. However, it becomes tractable, if the views are free-connex acyclic (i.e., in a nutshell, their body is (i) acyclic and (ii) remains acyclic if their head is added as an additional atom).
Cite as

Gaetano Geck, Jens Keppeler, Thomas Schwentick, and Christopher Spinrath. Rewriting with Acyclic Queries: Mind Your Head. In 25th International Conference on Database Theory (ICDT 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 220, pp. 8:1-8:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{geck_et_al:LIPIcs.ICDT.2022.8,
  author =	{Geck, Gaetano and Keppeler, Jens and Schwentick, Thomas and Spinrath, Christopher},
  title =	{{Rewriting with Acyclic Queries: Mind Your Head}},
  booktitle =	{25th International Conference on Database Theory (ICDT 2022)},
  pages =	{8:1--8:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-223-5},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{220},
  editor =	{Olteanu, Dan and Vortmeier, Nils},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2022.8},
  URN =		{urn:nbn:de:0030-drops-158829},
  doi =		{10.4230/LIPIcs.ICDT.2022.8},
  annote =	{Keywords: rewriting, acyclic rewriting, acyclic conjunctive queries, free-connex queries, hierarchical queries, NP-hardness}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2020.13
Distribution Constraints: The Chase for Distributed Data

Authors: Gaetano Geck, Frank Neven, and Thomas Schwentick

Published in: LIPIcs, Volume 155, 23rd International Conference on Database Theory (ICDT 2020)

Abstract
This paper introduces a declarative framework to specify and reason about distributions of data over computing nodes in a distributed setting. More specifically, it proposes distribution constraints which are tuple and equality generating dependencies (tgds and egds) extended with node variables ranging over computing nodes. In particular, they can express co-partitioning constraints and constraints about range-based data distributions by using comparison atoms. The main technical contribution is the study of the implication problem of distribution constraints. While implication is undecidable in general, relevant fragments of so-called data-full constraints are exhibited for which the corresponding implication problems are complete for EXPTIME, PSPACE and NP. These results yield bounds on deciding parallel-correctness for conjunctive queries in the presence of distribution constraints.
Cite as

Gaetano Geck, Frank Neven, and Thomas Schwentick. Distribution Constraints: The Chase for Distributed Data. In 23rd International Conference on Database Theory (ICDT 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 155, pp. 13:1-13:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{geck_et_al:LIPIcs.ICDT.2020.13,
  author =	{Geck, Gaetano and Neven, Frank and Schwentick, Thomas},
  title =	{{Distribution Constraints: The Chase for Distributed Data}},
  booktitle =	{23rd International Conference on Database Theory (ICDT 2020)},
  pages =	{13:1--13:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-139-9},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{155},
  editor =	{Lutz, Carsten and Jung, Jean Christoph},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2020.13},
  URN =		{urn:nbn:de:0030-drops-119378},
  doi =		{10.4230/LIPIcs.ICDT.2020.13},
  annote =	{Keywords: tuple-generating dependencies, chase, conjunctive queries, distributed evaluation}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2019.14
Parallel-Correctness and Parallel-Boundedness for Datalog Programs

Authors: Frank Neven, Thomas Schwentick, Christopher Spinrath, and Brecht Vandevoort

Published in: LIPIcs, Volume 127, 22nd International Conference on Database Theory (ICDT 2019)

Abstract
Recently, Ketsman et al. started the investigation of the parallel evaluation of recursive queries in the Massively Parallel Communication (MPC) model. Among other things, it was shown that parallel-correctness and parallel-boundedness for general Datalog programs is undecidable, by a reduction from the undecidable containment problem for Datalog. Furthermore, economic policies were introduced as a means to specify data distribution in a recursive setting. In this paper, we extend the latter framework to account for more general distributed evaluation strategies in terms of communication policies. We then show that the undecidability of parallel-correctness runs deeper: it already holds for fragments of Datalog, e.g., monadic and frontier-guarded Datalog, with a decidable containment problem, under relatively simple evaluation strategies. These simple evaluation strategies are defined w.r.t. data-moving distribution constraints. We then investigate restrictions of economic policies that yield decidability. In particular, we show that parallel-correctness is 2EXPTIME-complete for monadic and frontier-guarded Datalog under hash-based economic policies. Next, we consider restrictions of data-moving constraints and show that parallel-correctness and parallel-boundedness are 2EXPTIME-complete for frontier-guarded Datalog. Interestingly, distributed evaluation no longer preserves the usual containment relationships between fragments of Datalog. Indeed, not every monadic Datalog program is equivalent to a frontier-guarded one in the distributed setting. We illustrate the latter by considering two alternative settings where in one of these parallel-correctness is decidable for frontier-guarded Datalog but undecidable for monadic Datalog.
Cite as

Frank Neven, Thomas Schwentick, Christopher Spinrath, and Brecht Vandevoort. Parallel-Correctness and Parallel-Boundedness for Datalog Programs. In 22nd International Conference on Database Theory (ICDT 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 127, pp. 14:1-14:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{neven_et_al:LIPIcs.ICDT.2019.14,
  author =	{Neven, Frank and Schwentick, Thomas and Spinrath, Christopher and Vandevoort, Brecht},
  title =	{{Parallel-Correctness and Parallel-Boundedness for Datalog Programs}},
  booktitle =	{22nd International Conference on Database Theory (ICDT 2019)},
  pages =	{14:1--14:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-101-6},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{127},
  editor =	{Barcelo, Pablo and Calautti, Marco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2019.14},
  URN =		{urn:nbn:de:0030-drops-103165},
  doi =		{10.4230/LIPIcs.ICDT.2019.14},
  annote =	{Keywords: Datalog, distributed databases, distributed evaluation, decision problems, complexity}
}
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