46 Search Results for "Vianu, Victor"

Document
Research
DOI: 10.4230/TGDK.4.1.4
Native Provenance Computation for Federated and Non-Federated SPARQL Queries

Authors: Zubaria Asma, Daniel Hernández, Luis Galárraga, Giorgos Flouris, Irini Fundulaki, and Katja Hose

Published in: TGDK, Volume 4, Issue 1 (2026). Transactions on Graph Data and Knowledge, Volume 4, Issue 1

Abstract
The popularity of knowledge graphs (KGs) owes credit to their flexible data model, which is suitable for data integration from multiple sources. Several KG-based applications, such as trust assessment, view maintenance, or data valuation on dynamic data, rely on the ability to compute provenance explanations for query results. This need becomes more urgent in federated query processing systems, which allow the online consumption of heterogeneous and decentralized Web data. However, the problem of computing and interacting with provenance has received little attention, especially in the federated setting. On those grounds, this paper introduces the NPCS (Native Provenance Computation for SPARQL) approach, and its federated variant Fed-NPCS, that compute provenance for SPARQL query results. Both approaches build upon spm-semirings to annotate the results of monotonic and non-monotonic SPARQL queries with their provenance. Due to their reliance on query rewriting techniques, the approaches are directly applicable to already deployed SPARQL engines and federations using different reification schemes, including RDF-star. Our experimental evaluation shows that our novel query rewriting approach brings significant run-time improvements w.r.t. the state-of-the-art across both centralized and federated settings. In centralized settings, our tests on two popular SPARQL engines (GraphDB and Stardog) reveal substantial runtime gains over existing query rewriting solutions, enabling scalability to RDF graphs with billions of triples. In federated settings, our experiments on the FedShop benchmark with GraphDB show the viability of Fed-NPCS for federations with up to 200 sources.
Cite as

Zubaria Asma, Daniel Hernández, Luis Galárraga, Giorgos Flouris, Irini Fundulaki, and Katja Hose. Native Provenance Computation for Federated and Non-Federated SPARQL Queries. In Transactions on Graph Data and Knowledge (TGDK), Volume 4, Issue 1, pp. 4:1-4:43, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@Article{asma_et_al:TGDK.4.1.4,
  author =	{Asma, Zubaria and Hern\'{a}ndez, Daniel and Gal\'{a}rraga, Luis and Flouris, Giorgos and Fundulaki, Irini and Hose, Katja},
  title =	{{Native Provenance Computation for Federated and Non-Federated SPARQL Queries}},
  journal =	{Transactions on Graph Data and Knowledge},
  pages =	{4:1--4:43},
  ISSN =	{2942-7517},
  year =	{2026},
  volume =	{4},
  number =	{1},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/TGDK.4.1.4},
  URN =		{urn:nbn:de:0030-drops-259642},
  doi =		{10.4230/TGDK.4.1.4},
  annote =	{Keywords: native provenance computation, federated SPARQL queries, data provenance, NPCS, Fed-NPCS}
}
Document
DOI: 10.4230/OASIcs.FMBC.2026.8
Detecting Cross-Function Reentrancy from EVM Traces

Authors: Semia Guesmi, Carla Piazza, Andrea Gasparetto, Matteo Rizzo, and Sabina Rossi

Published in: OASIcs, Volume 142, 7th International Workshop on Formal Methods for Blockchains (FMBC 2026)

Abstract
Reentrancy remains one of the most critical vulnerabilities affecting Ethereum smart contracts. While many existing analysis tools focus on detecting classical single-function reentrancy, more complex forms such as cross-function reentrancy are harder to identify because they depend on execution semantics and interactions between multiple functions. In this work, we study reentrancy at the level of Ethereum Virtual Machine (EVM) execution traces. We extend the TxSpector framework with new Datalog-based detection rules designed to capture cross-function reentrancy patterns. To support this analysis, we also modernize the trace extraction component by adapting it to recent versions of the Ethereum client and updated EVM instructions. The proposed approach is evaluated on real Ethereum on-chain transaction traces. The results show that our method is able to detect cross-function reentrancy behaviors that are not captured by the original TxSpector rules, demonstrating the effectiveness of pattern-based logic detection at the EVM execution level.
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Semia Guesmi, Carla Piazza, Andrea Gasparetto, Matteo Rizzo, and Sabina Rossi. Detecting Cross-Function Reentrancy from EVM Traces. In 7th International Workshop on Formal Methods for Blockchains (FMBC 2026). Open Access Series in Informatics (OASIcs), Volume 142, pp. 8:1-8:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{guesmi_et_al:OASIcs.FMBC.2026.8,
  author =	{Guesmi, Semia and Piazza, Carla and Gasparetto, Andrea and Rizzo, Matteo and Rossi, Sabina},
  title =	{{Detecting Cross-Function Reentrancy from EVM Traces}},
  booktitle =	{7th International Workshop on Formal Methods for Blockchains (FMBC 2026)},
  pages =	{8:1--8:15},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-424-6},
  ISSN =	{2190-6807},
  year =	{2026},
  volume =	{142},
  editor =	{Bartoletti, Massimo and Marmsoler, Diego},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.FMBC.2026.8},
  URN =		{urn:nbn:de:0030-drops-257058},
  doi =		{10.4230/OASIcs.FMBC.2026.8},
  annote =	{Keywords: Blockchain, smart contract, Reentrancy detection, EVM, design Patterns, logic rules}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2026.4
Computing Consistent Least Upper Bounds in Aggregate Logic

Authors: Aziz Amezian El Khalfioui and Jef Wijsen

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract
We consider the problem of answering conjunctive queries with aggregation on database instances that may violate primary key constraints. In SQL, these queries follow the SELECT-FROM-WHERE-GROUP BY format, where the WHERE clause involves a conjunction of equalities, and the SELECT clause can incorporate aggregate operators like MAX, MIN, SUM, AVG, or COUNT. Repairs of a database instance are defined as inclusion-maximal subsets that satisfy all primary keys. The range-consistent answer to a numerical query over an inconsistent database is a pair [glb, lub], where glb and lub are, respectively, the smallest and the greatest results returned by the query over all possible repairs. While previous work has focused on the computation of the glb, the current paper studies the computation of the lub for a numerical domain of non-negative rational numbers. We introduce the notion of κ-acyclicity for self-join-free conjunctive queries. We show that if the body of a SUM-query is κ-acyclic, then the lub can be computed through a rewriting in first-order aggregate logic. Moreover, we show that this result extends to all aggregate operators that are monotone and associative. Importantly, we also prove the inverse: if the body of a SUM-query is not κ-acyclic, then the lub cannot be computed in first-order aggregate logic.
Cite as

Aziz Amezian El Khalfioui and Jef Wijsen. Computing Consistent Least Upper Bounds in Aggregate Logic. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 4:1-4:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{amezianelkhalfioui_et_al:LIPIcs.ICDT.2026.4,
  author =	{Amezian El Khalfioui, Aziz and Wijsen, Jef},
  title =	{{Computing Consistent Least Upper Bounds in Aggregate Logic}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{4:1--4:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.4},
  URN =		{urn:nbn:de:0030-drops-256180},
  doi =		{10.4230/LIPIcs.ICDT.2026.4},
  annote =	{Keywords: Consistent query answering, primary key, conjunctive query, aggregate logic}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2026.5
Rule Rewriting Revisited: A Fresh Look at Static Filtering for Datalog and ASP

Authors: Philipp Hanisch and Markus Krötzsch

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract
Static filtering is a data-independent optimisation method for Datalog, which generalises algebraic query rewriting techniques from relational databases. In spite of its early discovery by Kifer and Lozinskii in 1986, the method has been overlooked in recent research and system development, and special cases are being rediscovered independently. We therefore recall the original approach, using updated terminology and more general filter predicates that capture features of modern systems, and we show how to extend its applicability to answer set programming (ASP). The outcome is strictly more general but also more complex than the classical approach: double exponential in general and single exponential even for predicates of bounded arity. As a solution, we propose tractable approximations of the algorithm that can still yield much improved logic programs in typical cases, e.g., it can improve the performance of rule systems over real-world data in the order of magnitude.
Cite as

Philipp Hanisch and Markus Krötzsch. Rule Rewriting Revisited: A Fresh Look at Static Filtering for Datalog and ASP. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 5:1-5:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{hanisch_et_al:LIPIcs.ICDT.2026.5,
  author =	{Hanisch, Philipp and Kr\"{o}tzsch, Markus},
  title =	{{Rule Rewriting Revisited: A Fresh Look at Static Filtering for Datalog and ASP}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{5:1--5:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.5},
  URN =		{urn:nbn:de:0030-drops-256197},
  doi =		{10.4230/LIPIcs.ICDT.2026.5},
  annote =	{Keywords: Rule rewriting, static optimisation, static filtering, Datalog, Answer Set Programming}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2026.9
Acyclic Join Sampling Under Selections: Dichotomy, Union Sampling, and Enumeration

Authors: Jinchao Huang, Yufei Tao, and Sibo Wang

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract
Previous research on join sampling has focused on joins without selection conditions, even though such conditions are prevalent in everyday queries in database systems. Motivated by this, we undertake a systematic investigation on the complexity of sampling from the result of an acyclic join under equality conditions given only at runtime. When conditions are conjunctive, the goal is to understand when it is possible to precompute a feasible structure that uses Õ(IN) space and supports sampling in Õ(1) time, where IN is the input size. We present a dichotomy to characterize (subject to a widely-accepted conjecture) the existence of such structures based on the conditions supplied and, in every feasible scenario, give an optimal structure of O(IN) space and O(1) sample time. We then extend our investigation to conditions expressed in disjunctive normal form, where the core challenge reduces to the fundamental set union sampling problem. We overcome the challenge with an optimal algorithm and utilize it to develop optimal sampling structures. Our findings also lead to new results on the closely-related random enumeration problem.
Cite as

Jinchao Huang, Yufei Tao, and Sibo Wang. Acyclic Join Sampling Under Selections: Dichotomy, Union Sampling, and Enumeration. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 9:1-9:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{huang_et_al:LIPIcs.ICDT.2026.9,
  author =	{Huang, Jinchao and Tao, Yufei and Wang, Sibo},
  title =	{{Acyclic Join Sampling Under Selections: Dichotomy, Union Sampling, and Enumeration}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{9:1--9:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.9},
  URN =		{urn:nbn:de:0030-drops-256231},
  doi =		{10.4230/LIPIcs.ICDT.2026.9},
  annote =	{Keywords: Conjunctive Queries, Acyclic Joins, Sampling, Lower Bounds}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2026.12
The Complexity of Finding Missing Answer Repairs

Authors: Jesse Comer and Val Tannen

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract
We investigate the problem of identifying database repairs for missing tuples in query answers. We show that when the query is part of the input - the combined complexity setting - determining whether or not a repair exists is polynomial-time equivalent to the satisfiability problem for classes of queries admitting a weak form of projection and selection. We then identify the sub-classes of unions of conjunctive queries with negated atoms, defined by the relational algebra operations permitted to appear in the query, for which the minimal repair problem can be solved in polynomial time. In contrast, we show that the problem is NP-hard, as well as set cover-hard to approximate via strict reductions, whenever both projection and join are permitted in the input query. Additionally, we show that finding the size of a minimal repair for unions of conjunctive queries (with negated atoms permitted) is OptP[log(n)]-complete, while computing a minimal repair is possible with O(n²) queries to an NP oracle. With recursion permitted, the combined complexity of all of these variants increases significantly, with an EXP lower bound. However, from the data complexity perspective, we show that minimal repairs can be identified in polynomial time for all queries expressible as semi-positive datalog programs.
Cite as

Jesse Comer and Val Tannen. The Complexity of Finding Missing Answer Repairs. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 12:1-12:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{comer_et_al:LIPIcs.ICDT.2026.12,
  author =	{Comer, Jesse and Tannen, Val},
  title =	{{The Complexity of Finding Missing Answer Repairs}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{12:1--12:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.12},
  URN =		{urn:nbn:de:0030-drops-256265},
  doi =		{10.4230/LIPIcs.ICDT.2026.12},
  annote =	{Keywords: Missing answers, database repairs, datalog, computational complexity}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2026.13
Complexity of Evaluating GQL Queries

Authors: Diego Figueira, Anthony W. Lin, and Liat Peterfreund

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract
GQL has recently emerged as the standard query language over graph databases, particularly, property graphs. Indeed, this is analogous to the role of SQL for relational databases. Unlike SQL, however, fundamental problems regarding GQL are still unsolved, most notably the complexity of query evaluation. In this paper we provide a complete solution to this problem for the core fragment of GQL and for its extension with path restrictors. In particular, we show that the data complexity of these fragments is P^NP[log]-complete in general, and drops to NL-complete when restrictors are disallowed. Using techniques from embedded finite model theory, we show that this is true, even when the queries use data from infinite concrete domains such as real numbers with arithmetic. In proving these results, we establish and exploit tight connections between GQL and query languages over relational databases, especially extensions of relational calculus with transitive closure operators and fragments of second-order logic.
Cite as

Diego Figueira, Anthony W. Lin, and Liat Peterfreund. Complexity of Evaluating GQL Queries. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 13:1-13:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{figueira_et_al:LIPIcs.ICDT.2026.13,
  author =	{Figueira, Diego and Lin, Anthony W. and Peterfreund, Liat},
  title =	{{Complexity of Evaluating GQL Queries}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{13:1--13:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.13},
  URN =		{urn:nbn:de:0030-drops-256278},
  doi =		{10.4230/LIPIcs.ICDT.2026.13},
  annote =	{Keywords: Graph query languages, GQL, complexity, database theory}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2026.17
Algorithms for Optimizing Acyclic Queries

Authors: Zheng Luo, Wim Van den Broeck, Guy Van den Broeck, and Yisu Remy Wang

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract
Most research on query optimization has centered on binary join algorithms like hash join and sort-merge join. However, recent years have seen growing interest in theoretically optimal algorithms, notably Yannakakis' algorithm. These algorithms rely on join trees, which differ from the operator trees for binary joins and require new optimization techniques. We propose three approaches to constructing join trees for acyclic queries. First, we give an algorithm to enumerate all join trees of an α-acyclic query by edits in linear time with amortized constant delay, which forms the basis of a cost-based optimizer for acyclic joins. Second, we show the Maximum Cardinality Search algorithm by Tarjan and Yannakakis constructs the unique shallowest join tree for any Berge-acyclic query, thus enabling parallel execution of large join queries. Finally, we prove that a simple algorithm by Hu et al. converts any connected left-deep linear plan of a γ-acyclic query into a join tree, allowing reuse of optimizers developed for binary joins.
Cite as

Zheng Luo, Wim Van den Broeck, Guy Van den Broeck, and Yisu Remy Wang. Algorithms for Optimizing Acyclic Queries. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 17:1-17:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{luo_et_al:LIPIcs.ICDT.2026.17,
  author =	{Luo, Zheng and Van den Broeck, Wim and Van den Broeck, Guy and Wang, Yisu Remy},
  title =	{{Algorithms for Optimizing Acyclic Queries}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{17:1--17:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.17},
  URN =		{urn:nbn:de:0030-drops-256319},
  doi =		{10.4230/LIPIcs.ICDT.2026.17},
  annote =	{Keywords: Query Optimization, Join Trees, Enumeration}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2026.21
First-Order Rewritability of Rule-Based Ontology Mediated Queries with Negation

Authors: Georg Gottlob, Marco Manna, Andreas Pieris, and Aldo Ricioppo

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract
The idea of using an ontology to enrich user queries with domain knowledge has attracted considerable attention from the database and KR communities during the last fifteen years or so. The ontology and the user query can be conveniently seen as two components of one composite query, called ontology-mediated query (omq), while an omq language (OL,QL) collects all such omqs where the ontology is expressed using the ontology language OL and the user query comes from the query language QL. The evaluation problem for rule-based omq languages of the form (OL,CQ), where OL is a rule-based ontology language, i.e., it collects ontologies modelled using tuple-generating dependencies (a.k.a. existential rules), and CQ is the language of conjunctive queries, has been extensively studied in the literature. In particular, the notion of first-order rewritability of such languages, i.e., the property of being able to rewrite every omq from the language in question to an equivalent first-order query, has been studied in depth. This research effort led an algorithmic characterization of when a rule-based omq language (OL,CQ) is first-order rewritable. More precisely, there is a uniform algorithm Rewrite such that, for every rule-based ontology language OL, the omq language (OL,CQ) is first-order rewritable iff for every omq O from (OL,CQ), the algorithm Rewrite on input O terminates and constructs a first-order rewriting of O. The question that we are interested in is whether the above algorithmic characterization can be extended to rule-based omq languages of the form (OL,nCQ), where nCQ is the language of conjunctive queries with the useful feature of negation. The goal of this work is to initiate effort towards the settlement of the above highly non-trivial question. To this end, we provide a new algorithm, which is a non-trivial extension of the algorithm Rewrite for positive omqs, and show the following: under the Skolem semantics, a well-established approach for defining the answer to a rule-based omq when the user query can use negation, the proposed algorithm is a first-order rewriter for (OL,nCQ), where OL is the language of linear or acyclic tuple-generating dependencies, two central rule-based ontology languages that ensure first-order rewritability for positive omqs. We strongly believe that the new algorithm can serve as a good starting point towards the full settlement of our main question.
Cite as

Georg Gottlob, Marco Manna, Andreas Pieris, and Aldo Ricioppo. First-Order Rewritability of Rule-Based Ontology Mediated Queries with Negation. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 21:1-21:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{gottlob_et_al:LIPIcs.ICDT.2026.21,
  author =	{Gottlob, Georg and Manna, Marco and Pieris, Andreas and Ricioppo, Aldo},
  title =	{{First-Order Rewritability of Rule-Based Ontology Mediated Queries with Negation}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{21:1--21:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.21},
  URN =		{urn:nbn:de:0030-drops-256353},
  doi =		{10.4230/LIPIcs.ICDT.2026.21},
  annote =	{Keywords: ontology-mediated queries, tuple-generating dependencies, conjunctive queries with negation, first-order rewritability}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2026.22
View-Based Query Determinacy for Walk-Based Semantics

Authors: Nadime Francis

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract
The view-based query determinacy problem asks, given a view 𝒱 and a query Q whether the information contained in 𝒱 always suffices to answer the query Q. It is a notoriously hard problem that is known to be undecidable even in very restricted settings. Here, we study it in the context of graph databases and regular path queries and views evaluated under several "walk-based semantics", that is, semantics in which queries and views return the matched walks in full as opposed to the classical "endpoint semantics". Our main finding is that view-based query determinacy is decidable for regular path queries under both trail and shortest walk semantics.
Cite as

Nadime Francis. View-Based Query Determinacy for Walk-Based Semantics. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 22:1-22:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{francis:LIPIcs.ICDT.2026.22,
  author =	{Francis, Nadime},
  title =	{{View-Based Query Determinacy for Walk-Based Semantics}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{22:1--22:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.22},
  URN =		{urn:nbn:de:0030-drops-256362},
  doi =		{10.4230/LIPIcs.ICDT.2026.22},
  annote =	{Keywords: graph databases, regular path queries, trail semantics, shortest walk semantics, view-based query determinacy}
}
Document
Database Theory in Action
DOI: 10.4230/LIPIcs.ICDT.2026.28
Database Theory in Action: Learning Logical Modelling with Iltis

Authors: Tristan Kneisel, Fabian Vehlken, and Thomas Zeume

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract
Important learning objectives in database education are to learn how to design database schemas and how to write queries to access data stored in a database adhering to a schema. In this article we report on results from [Tristan Kneisel et al., 2025] where this learning objective is addressed for the related educational task of modelling with logical formalisms. Two key steps in logical modelling are to (a) choose a suitable vocabulary, that is, e.g., which first-order symbols to use and with which intended meaning, and then to (b) construct actual formal descriptions, i.e. first-order formulas over the chosen vocabulary. While (b) is addressed by several educational support systems for formal foundations of computer science, (a) is so far not addressed at all - likely because it involves specifying the intended meaning of symbols in natural language. We propose a conceptual framework for educational tasks where students choose a vocabulary and implement it for tasks for designing propositional and first-order vocabularies within the Iltis educational system.
Cite as

Tristan Kneisel, Fabian Vehlken, and Thomas Zeume. Database Theory in Action: Learning Logical Modelling with Iltis. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 28:1-28:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{kneisel_et_al:LIPIcs.ICDT.2026.28,
  author =	{Kneisel, Tristan and Vehlken, Fabian and Zeume, Thomas},
  title =	{{Database Theory in Action: Learning Logical Modelling with Iltis}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{28:1--28:5},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.28},
  URN =		{urn:nbn:de:0030-drops-256426},
  doi =		{10.4230/LIPIcs.ICDT.2026.28},
  annote =	{Keywords: Educational support systems, Logic, Database theory, Natural language processing}
}
Document
DOI: 10.4230/LIPIcs.CSL.2026.10
Disjunctions of Two Dependence Atoms

Authors: Nicolas Fröhlich, Phokion G. Kolaitis, and Arne Meier

Published in: LIPIcs, Volume 363, 34th EACSL Annual Conference on Computer Science Logic (CSL 2026)

Abstract
Dependence logic is a formalism that augments the syntax of first-order logic with dependence atoms asserting that the value of a variable is determined by the values of some other variables, i.e., dependence atoms express functional dependencies in relational databases. On finite structures, dependence logic captures NP, hence there are sentences of dependence logic whose model-checking problem is NP-complete. In fact, it is known that there are disjunctions of three dependence atoms whose model-checking problem is NP-complete. Motivated from considerations in database theory, we study the model-checking problem for disjunctions of two unary dependence atoms and establish a trichotomy theorem, namely, for every such formula, one of the following is true for the model-checking problem: (i) it is NL-complete; (ii) it is L-complete; (iii) it is first-order definable (hence, in AC⁰). Furthermore, we classify the complexity of the model-checking problem for disjunctions of two arbitrary dependence atoms, and also characterize when such a disjunction is coherent, i.e., when it satisfies a certain small-model property. Along the way, we identify a new class of 2CNF-formulas whose satisfiability problem is L-complete.
Cite as

Nicolas Fröhlich, Phokion G. Kolaitis, and Arne Meier. Disjunctions of Two Dependence Atoms. In 34th EACSL Annual Conference on Computer Science Logic (CSL 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 363, pp. 10:1-10:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{frohlich_et_al:LIPIcs.CSL.2026.10,
  author =	{Fr\"{o}hlich, Nicolas and Kolaitis, Phokion G. and Meier, Arne},
  title =	{{Disjunctions of Two Dependence Atoms}},
  booktitle =	{34th EACSL Annual Conference on Computer Science Logic (CSL 2026)},
  pages =	{10:1--10:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-411-6},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{363},
  editor =	{Guerrini, Stefano and K\"{o}nig, Barbara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2026.10},
  URN =		{urn:nbn:de:0030-drops-254343},
  doi =		{10.4230/LIPIcs.CSL.2026.10},
  annote =	{Keywords: Dependence logic, coherence, model-checking, complexity, functional dependencies}
}
Document
Invited Paper
DOI: 10.4230/OASIcs.RW.2024/2025.7
Modern Datalog: Concepts, Methods, Applications (Invited Paper)

Authors: Markus Krötzsch

Published in: OASIcs, Volume 138, Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 & RW 2025)

Abstract
Pure Datalog is arguably the most fundamental rule language, elegant and simple, but also often too limited to be useful in practice. This has motivated the introduction of many new expressive features, ranging from datatypes and related functions, over aggregates and semi-ring generalisations, to existential quantifiers and complex terms. In spite of their variety, all these approaches remain true to the nature of Datalog as a direct, pattern-based way of computing on structured data. We therefore find that a modern notion of Datalog is emerging, distinctly different from other approaches of logic programming and with its own set of related methods and applications. In this course, we introduce Datalog and its most common extensions, and explain when and how these features can be used together (which is often, but not always, safe to do). We further look at modern Datalog systems and some of their primary use cases. Hands-on work with Datalog and its extensions is done with the free Datalog engine https://knowsys.github.io/nemo-doc/. The course is accessible to all audiences and does not assume specific prior knowledge.
Cite as

Markus Krötzsch. Modern Datalog: Concepts, Methods, Applications (Invited Paper). In Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 & RW 2025). Open Access Series in Informatics (OASIcs), Volume 138, pp. 7:1-7:41, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{krotzsch:OASIcs.RW.2024/2025.7,
  author =	{Kr\"{o}tzsch, Markus},
  title =	{{Modern Datalog: Concepts, Methods, Applications}},
  booktitle =	{Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 \& RW 2025)},
  pages =	{7:1--7:41},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-405-5},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{138},
  editor =	{Artale, Alessandro and Bienvenu, Meghyn and Garc{\'\i}a, Yazm{\'\i}n Ib\'{a}\~{n}ez and Murlak, Filip},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.RW.2024/2025.7},
  URN =		{urn:nbn:de:0030-drops-250524},
  doi =		{10.4230/OASIcs.RW.2024/2025.7},
  annote =	{Keywords: Datalog, query language, knowlegde representation and reasoning, logic programming, Horn logic, SPARQL, datatypes and aggregation, lecture notes, tutorial}
}
Document
Invited Paper
DOI: 10.4230/OASIcs.RW.2024/2025.5
Inconsistency-Tolerant Semantics Based on (Preferred) Repairs (Invited Paper)

Authors: Camille Bourgaux

Published in: OASIcs, Volume 138, Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 & RW 2025)

Abstract
Real-world datasets are plagued by data quality issues which may render the data inconsistent w.r.t. a set of constraints, be they given by database integrity constraints or ontologies. A prominent way to handle such inconsistent data is to use inconsistency-tolerant semantics to obtain meaningful answers to queries. Most of these semantics are based on some notion of repairs, which represent ways of restoring the data consistency. The most basic kind of repairs is that of subset repairs, which are maximal consistent subsets of the dataset. However, in many scenarios, one can define preferred repairs based on some preference information. These lecture notes present inconsistency-tolerant semantics, focusing on the repair-based ones, then review different kinds of preferred repairs that have been considered in the literature. We present in particular the relationships between different kinds of preferred repairs and other notions related to inconsistency handling, the computational complexity of reasoning with (preferred) repairs, and some implementations.
Cite as

Camille Bourgaux. Inconsistency-Tolerant Semantics Based on (Preferred) Repairs (Invited Paper). In Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 & RW 2025). Open Access Series in Informatics (OASIcs), Volume 138, pp. 5:1-5:67, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{bourgaux:OASIcs.RW.2024/2025.5,
  author =	{Bourgaux, Camille},
  title =	{{Inconsistency-Tolerant Semantics Based on (Preferred) Repairs}},
  booktitle =	{Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 \& RW 2025)},
  pages =	{5:1--5:67},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-405-5},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{138},
  editor =	{Artale, Alessandro and Bienvenu, Meghyn and Garc{\'\i}a, Yazm{\'\i}n Ib\'{a}\~{n}ez and Murlak, Filip},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.RW.2024/2025.5},
  URN =		{urn:nbn:de:0030-drops-250504},
  doi =		{10.4230/OASIcs.RW.2024/2025.5},
  annote =	{Keywords: Knowledge bases, databases, inconsistency handling, repairs, preferences}
}
Document
Invited Paper
DOI: 10.4230/OASIcs.RW.2024/2025.9
Reasoning About Time in DatalogMTL: Course Notes (Invited Paper)

Authors: Przemysław Andrzej Wałęga

Published in: OASIcs, Volume 138, Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 & RW 2025)

Abstract
Many real-world applications, such as those in healthcare, finance, and logistics, require reasoning over temporal data. Standard rule-based languages like Datalog, however, lack explicit mechanisms for handling time and temporal dependencies. In this chapter, we discussDatalogMTL, an extension of Datalog with operators frommetric temporal logic that allow to express complex temporal properties. We focus on reasoning algorithms for DatalogMTL, discussing bothmaterialisation, based on fixpoint applications of the immediate consequence operator, and anovel saturation-based extensionthat detects and halts infinite derivations, ensuring both completeness and termination of reasoning.
Cite as

Przemysław Andrzej Wałęga. Reasoning About Time in DatalogMTL: Course Notes (Invited Paper). In Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 & RW 2025). Open Access Series in Informatics (OASIcs), Volume 138, pp. 9:1-9:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{walega:OASIcs.RW.2024/2025.9,
  author =	{Wa{\l}\k{e}ga, Przemys{\l}aw Andrzej},
  title =	{{Reasoning About Time in DatalogMTL: Course Notes}},
  booktitle =	{Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 \& RW 2025)},
  pages =	{9:1--9:23},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-405-5},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{138},
  editor =	{Artale, Alessandro and Bienvenu, Meghyn and Garc{\'\i}a, Yazm{\'\i}n Ib\'{a}\~{n}ez and Murlak, Filip},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.RW.2024/2025.9},
  URN =		{urn:nbn:de:0030-drops-250546},
  doi =		{10.4230/OASIcs.RW.2024/2025.9},
  annote =	{Keywords: DatalogMTL, Logic Programming, Temporal Reasoning}
}
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