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Documents authored by Feier, Cristina

Document
DOI: 10.4230/LIPIcs.ICDT.2024.22
Evaluating Graph Queries Using Semantic Treewidth

Authors: Cristina Feier, Tomasz Gogacz, and Filip Murlak

Published in: LIPIcs, Volume 290, 27th International Conference on Database Theory (ICDT 2024)

Abstract
Unions of conjunctive two-way regular path queries (UC2RPQs) are a common abstraction of query languages for graph databases, much like unions of conjunctive queries (UCQs) in the relational case. As in the case of UCQs, their evaluation is NP-complete in combined complexity. Semantic tree-width, i.e. the minimal treewidth of equivalent queries, has been proposed as a candidate criterion to characterize fixed-parameter tractability of UC2RPQs. It was recently shown how to decide the semantic tree-width of a UC2RPQ, by constructing the best under-approximation of a given treewidth, in the form of a UC2RPQ of size doubly exponential in the size of the original query. This leads to an fpt algorithm for evaluating UC2RPQs of semantic TW k which runs in time doubly exponential in the size of the parameter, i.e. in the UC2RPQ. Here we describe a more efficient fpt algorithm for evaluating UC2RPQs of semantic treewidth k which runs in time singly exponential in the size of the parameter. We do this by a careful construction of a witness query which, while still being doubly exponential, can be represented as a Datalog program of bounded width and singly exponential size.
Cite as

Cristina Feier, Tomasz Gogacz, and Filip Murlak. Evaluating Graph Queries Using Semantic Treewidth. In 27th International Conference on Database Theory (ICDT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 290, pp. 22:1-22:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{feier_et_al:LIPIcs.ICDT.2024.22,
  author =	{Feier, Cristina and Gogacz, Tomasz and Murlak, Filip},
  title =	{{Evaluating Graph Queries Using Semantic Treewidth}},
  booktitle =	{27th International Conference on Database Theory (ICDT 2024)},
  pages =	{22:1--22:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-312-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{290},
  editor =	{Cormode, Graham and Shekelyan, Michael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2024.22},
  URN =		{urn:nbn:de:0030-drops-198048},
  doi =		{10.4230/LIPIcs.ICDT.2024.22},
  annote =	{Keywords: conjunctive two-way regular path queries, fixed-parameter tractable evaluation, semantic treewidth, Datalog encoding, optimization}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2022.12
Characterising Fixed Parameter Tractability for Query Evaluation over Guarded TGDs

Authors: Cristina Feier

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

Abstract
We consider the parameterized complexity of evaluating Ontology Mediated Queries (OMQ) based on Guarded TGDs (GTGD) and Unions of Conjunctive Queries, in the case where relational symbols have unrestricted arity and where the parameter is the size of the OMQ. We establish exact criteria for fixed-parameter tractable (fpt) evaluation of recursively enumerable (r.e.) classes of such OMQs (under the widely held Exponential Time Hypothesis). One of the main technical tools introduced in the paper is an fpt-reduction from deciding parameterized uniform CSPs to parameterized OMQ evaluation. The reduction preserves measures known to be essential for classifying r.e. classes of parameterized uniform CSPs: submodular width (according to the well known result of Marx for unrestricted-arity schemas) and treewidth (according to the well known result of Grohe for bounded-arity schemas). As such, it can be employed to obtain hardness results for evaluation of r.e. classes of parameterized OMQs based on GTGD both in the unrestricted and in the bounded arity case. Previously, for bounded arity schemas, this has been tackled using a technique requiring full introspection into the construction employed by Grohe.
Cite as

Cristina Feier. Characterising Fixed Parameter Tractability for Query Evaluation over Guarded TGDs. In 25th International Conference on Database Theory (ICDT 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 220, pp. 12:1-12:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{feier:LIPIcs.ICDT.2022.12,
  author =	{Feier, Cristina},
  title =	{{Characterising Fixed Parameter Tractability for Query Evaluation over Guarded TGDs}},
  booktitle =	{25th International Conference on Database Theory (ICDT 2022)},
  pages =	{12:1--12:20},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2022.12},
  URN =		{urn:nbn:de:0030-drops-158869},
  doi =		{10.4230/LIPIcs.ICDT.2022.12},
  annote =	{Keywords: omq, fpt evaluation, guarded tgds, unbounded arity, submodular width}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2021.11
Answer Counting Under Guarded TGDs

Authors: Cristina Feier, Carsten Lutz, and Marcin Przybyłko

Published in: LIPIcs, Volume 186, 24th International Conference on Database Theory (ICDT 2021)

Abstract
We study the complexity of answer counting for ontology-mediated queries and for querying under constraints, considering conjunctive queries and unions thereof (UCQs) as the query language and guarded TGDs as the ontology and constraint language, respectively. Our main result is a classification according to whether answer counting is fixed-parameter tractable (FPT), W[1]-equivalent, #W[1]-equivalent, #W[2]-hard, or #A[2]-equivalent, lifting a recent classification for UCQs without ontologies and constraints due to Dell et al. [Holger Dell et al., 2019]. The classification pertains to various structural measures, namely treewidth, contract treewidth, starsize, and linked matching number. Our results rest on the assumption that the arity of relation symbols is bounded by a constant and, in the case of ontology-mediated querying, that all symbols from the ontology and query can occur in the data (so-called full data schema). We also study the meta-problems for the mentioned structural measures, that is, to decide whether a given ontology-mediated query or constraint-query specification is equivalent to one for which the structural measure is bounded.
Cite as

Cristina Feier, Carsten Lutz, and Marcin Przybyłko. Answer Counting Under Guarded TGDs. In 24th International Conference on Database Theory (ICDT 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 186, pp. 11:1-11:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{feier_et_al:LIPIcs.ICDT.2021.11,
  author =	{Feier, Cristina and Lutz, Carsten and Przyby{\l}ko, Marcin},
  title =	{{Answer Counting Under Guarded TGDs}},
  booktitle =	{24th International Conference on Database Theory (ICDT 2021)},
  pages =	{11:1--11:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-179-5},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{186},
  editor =	{Yi, Ke and Wei, Zhewei},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2021.11},
  URN =		{urn:nbn:de:0030-drops-137195},
  doi =		{10.4230/LIPIcs.ICDT.2021.11},
  annote =	{Keywords: Ontology-Mediated Querying, Querying under Constraints, Answer Counting, Parameterized Complexity}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.ICDT.2017.1
Rewritability in Monadic Disjunctive Datalog, MMSNP, and Expressive Description Logics (Invited Talk)

Authors: Cristina Feier, Antti Kuusisto, and Carsten Lutz

Published in: LIPIcs, Volume 68, 20th International Conference on Database Theory (ICDT 2017)

Abstract
We study rewritability of monadic disjunctive Datalog programs, (the complements of) MMSNP sentences, and ontology-mediated queries (OMQs) based on expressive description logics of the ALC family and on conjunctive queries. We show that rewritability into FO and into monadic Datalog (MDLog) are decidable, and that rewritability into Datalog is decidable when the original query satisfies a certain condition related to equality. We establish 2NExpTime-completeness for all studied problems except rewritability into MDLog for which there remains a gap between 2NExpTime and 3ExpTime. We also analyze the shape of rewritings, which in the MMSNP case correspond to obstructions, and give a new construction of canonical Datalog programs that is more elementary than existing ones and also applies to non-Boolean queries.
Cite as

Cristina Feier, Antti Kuusisto, and Carsten Lutz. Rewritability in Monadic Disjunctive Datalog, MMSNP, and Expressive Description Logics (Invited Talk). In 20th International Conference on Database Theory (ICDT 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 68, pp. 1:1-1:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{feier_et_al:LIPIcs.ICDT.2017.1,
  author =	{Feier, Cristina and Kuusisto, Antti and Lutz, Carsten},
  title =	{{Rewritability in Monadic Disjunctive Datalog, MMSNP, and Expressive Description Logics}},
  booktitle =	{20th International Conference on Database Theory (ICDT 2017)},
  pages =	{1:1--1:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-024-8},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{68},
  editor =	{Benedikt, Michael and Orsi, Giorgio},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2017.1},
  URN =		{urn:nbn:de:0030-drops-70636},
  doi =		{10.4230/LIPIcs.ICDT.2017.1},
  annote =	{Keywords: FO-Rewritability, MDDLog, MMSNP, DL, ontology mediated queries}
}
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