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LIPIcs, Volume 365
29th International Conference on Database Theory (ICDT 2026)
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Leibniz International Proceedings in Informatics (LIPIcs)
Conference: International Conference on Database Theory (ICDT)
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- published at: 2026-03-18
- Publisher: Schloss Dagstuhl – Leibniz-Zentrum für Informatik
- ISBN: 978-3-95977-413-0
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Complete Volume
LIPIcs, Volume 365, ICDT 2026, Complete Volume
Abstract
LIPIcs, Volume 365, ICDT 2026, Complete Volume
Cite as
29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 1-486, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@Proceedings{tencate_et_al:LIPIcs.ICDT.2026,
title = {{LIPIcs, Volume 365, ICDT 2026, Complete Volume}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {1--486},
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},
URN = {urn:nbn:de:0030-drops-256660},
doi = {10.4230/LIPIcs.ICDT.2026},
annote = {Keywords: LIPIcs, Volume 365, ICDT 2026, Complete Volume}
}
Document
Front Matter
Front Matter, Table of Contents, Preface, Conference Organization
Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as
29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 0:i-0:xvi, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{tencate_et_al:LIPIcs.ICDT.2026.0,
author = {ten Cate, Balder and Funk, Maurice},
title = {{Front Matter, Table of Contents, Preface, Conference Organization}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {0:i--0:xvi},
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.2026.0},
URN = {urn:nbn:de:0030-drops-256655},
doi = {10.4230/LIPIcs.ICDT.2026.0},
annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
Invited Talk
Query Decompositions and All That (Invited Talk)
Abstract
The close relationship between Conjunctive Queries (CQs) and Constraint Satisfaction Problems (CSPs) has long been known. Nevertheless, apart from decomposition methods, research on efficient query evaluation or constraint solving algorithms has developed rather independently. In this article, we illustrate how search algorithms originating from the CSP community can be fruitfully applied to query evaluation - either by further developing the original search algorithms or by combining them with query decomposition methods. It turns out that the resulting approaches may indeed lead to lower time and/or space complexity than previous query evaluation methods.
Cite as
Kyle Deeds, Timo Camillo Merkl, Reinhard Pichler, and Dan Suciu. Query Decompositions and All That (Invited Talk). In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 1:1-1:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{deeds_et_al:LIPIcs.ICDT.2026.1,
author = {Deeds, Kyle and Merkl, Timo Camillo and Pichler, Reinhard and Suciu, Dan},
title = {{Query Decompositions and All That}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {1:1--1:20},
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.2026.1},
URN = {urn:nbn:de:0030-drops-256158},
doi = {10.4230/LIPIcs.ICDT.2026.1},
annote = {Keywords: Query evaluation, Query decompositions, Complexity}
}
Document
Invited Talk
The Dissection of a Complex Event Recognition Engine (Invited Talk)
Abstract
Complex Event Recognition (CER) is a group of data management technologies that model data streams as sequences of events, where users are interested in recognizing complex events, namely, groups of events that represent critical situations in real life. Examples of complex events could include a fire detected by a sensor network in a nature reserve, an accident recognized by cameras in a smart city, or a critical social event in a social network. In these scenarios, event streams are generated continuously at high speed, and the importance of each event decays rapidly over time. To process them, a complex event recognition engine is a data management software that must efficiently process such data and alert on the presence of complex events in real time.
In this talk, we will present the dissection of CORE [Kyle Bossonney et al., 2025; Marco Bucchi et al., 2022], a novel complex event recognition engine. The dissection will cover all its internal components: starting with its architecture, we will examine its query language, stream and memory management, query optimization, query evaluation, and complex event outputting. We will focus on the technical solutions and challenges of a CER engine, from both theoretical [Alejandro Grez et al., 2019; Alejandro Grez et al., 2021] and practical [Kyle Bossonney et al., 2025; Marco Bucchi et al., 2022] perspectives. In particular, based on our understanding of its components, we will review several open research problems and possible directions for future work in complex event recognition.
Cite as
Cristian Riveros. The Dissection of a Complex Event Recognition Engine (Invited Talk). In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{riveros:LIPIcs.ICDT.2026.2,
author = {Riveros, Cristian},
title = {{The Dissection of a Complex Event Recognition Engine}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {2:1--2:1},
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.2026.2},
URN = {urn:nbn:de:0030-drops-256169},
doi = {10.4230/LIPIcs.ICDT.2026.2},
annote = {Keywords: Streams, complex event recognition, query evaluation, query optimization}
}
Document
Invited Talk
Building Relational Circuits (Invited Talk)
Abstract
We review two algorithms which allow to build a factorized representation of the answers set of join queries. In a nutshell, the representation builds a circuit representing the answers set of a join query by starting from atomic relations and iteratively combine them by either constructing the Cartesian product or the disjoint union of previously computed relations. The first one can be seen as the trace of the celebrated Yannakakis algorithm, building the answer set from the inputs to the output of the circuit while the second adopts a top-down approach which can be seen as a generalization of the exhaustive DPLL algorithm, originally designed to solve the #SAT problem.
Cite as
Florent Capelli. Building Relational Circuits (Invited Talk). In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 3:1-3:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{capelli:LIPIcs.ICDT.2026.3,
author = {Capelli, Florent},
title = {{Building Relational Circuits}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {3:1--3:20},
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.2026.3},
URN = {urn:nbn:de:0030-drops-256172},
doi = {10.4230/LIPIcs.ICDT.2026.3},
annote = {Keywords: Conjunctive queries, factorized databases, knowledge compilation}
}
Document
Computing Consistent Least Upper Bounds in Aggregate Logic
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
Rule Rewriting Revisited: A Fresh Look at Static Filtering for Datalog and ASP
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
Designing and Comparing RPQ Semantics
Abstract
Modern Property graph database query languages such as Cypher, PGQL, GSQL, and the standard GQL draw inspiration from the formalism of regular path queries (RPQs). In order to output walks explicitly, they depart from the classical and well-studied homomorphism semantics. However, it then becomes difficult to present results to users because RPQs may match infinitely many walks. The aforementioned languages use ad-hoc criteria to select a finite subset of those matches. For instance, Cypher uses trail semantics, discarding walks with repeated edges; PGQL and GSQL use shortest walk semantics, retaining only the walks of minimal length among all matched walks; and GQL allows users to choose from several semantics. Even though there is academic research on these semantics, it focuses almost exclusively on evaluation efficiency.
In an attempt to better understand, choose and design RPQ semantics, we present a framework to categorize and compare them according to other criteria. We formalize several possible properties, pertaining to the study of RPQ semantics seen as mathematical functions mapping a database and a query to a finite set of walks. We show that some properties are mutually exclusive, or cannot be met. We also give several new RPQ semantics as examples. Some of them may provide ideas for the design of new semantics for future graph database query languages.
Cite as
Victor Marsault and Antoine Meyer. Designing and Comparing RPQ Semantics. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 6:1-6:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{marsault_et_al:LIPIcs.ICDT.2026.6,
author = {Marsault, Victor and Meyer, Antoine},
title = {{Designing and Comparing RPQ Semantics}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {6:1--6:20},
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.2026.6},
URN = {urn:nbn:de:0030-drops-256200},
doi = {10.4230/LIPIcs.ICDT.2026.6},
annote = {Keywords: Regular Path Queries, RPQ, Semantics, Graph Databases, Pattern matching, Regular Expression}
}
Document
The Importance of Parameters in Ranking Functions
Abstract
How important is the weight of a given column in determining the ranking of tuples in a table? To address such an explanation question about a ranking function, we investigate the computation of SHAP scores for column weights, adopting a recent framework by Grohe et al. [ICDT'24]. The exact definition of this score depends on three key components: (1) the ranking function in use, (2) an effect function that quantifies the impact of using alternative weights on the ranking, and (3) an underlying weight distribution. We analyze the computational complexity of different instantiations of this framework for a range of fundamental ranking and effect functions, focusing on probabilistically independent finite distributions for individual columns.
For the ranking functions, we examine lexicographic orders and score-based orders defined by the summation, minimum, and maximum functions. For the effect functions, we consider global, top-k, and local perspectives: global measures quantify the divergence between the perturbed and original rankings, top-k measures inspect the change in the set of top-k answers, and local measures capture the impact on an individual tuple of interest. Although all cases admit an additive fully polynomial-time randomized approximation scheme (FPRAS), we establish the complexity of exact computation, identifying which cases are solvable in polynomial time and which are #P-hard. We further show that all complexity results, lower bounds and upper bounds, extend to a related task of computing the Shapley value of whole columns (regardless of their weight).
Cite as
Christoph Standke, Nikolaos Tziavelis, Wolfgang Gatterbauer, and Benny Kimelfeld. The Importance of Parameters in Ranking Functions. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 7:1-7:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{standke_et_al:LIPIcs.ICDT.2026.7,
author = {Standke, Christoph and Tziavelis, Nikolaos and Gatterbauer, Wolfgang and Kimelfeld, Benny},
title = {{The Importance of Parameters in Ranking Functions}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {7:1--7:18},
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.2026.7},
URN = {urn:nbn:de:0030-drops-256217},
doi = {10.4230/LIPIcs.ICDT.2026.7},
annote = {Keywords: Ranking, Explanation, Shapley value, SHAP scores}
}
Document
Neither Cover nor Pack: Distributed Worst-Case Optimality of Degree-2 Joins
Abstract
We study the worst-case communication complexity of the join query evaluation problem over large-scale data in distributed shared-nothing systems under the MPC model. We focus on multi-round MPC algorithms that run in constant number of rounds. The problem is well-understood for a few classes of queries, mainly the class of acyclic queries and the class of graph-like queries. For queries not belonging to either class, the complexity picture is much less clear. We study the class of degree-two queries and fragments thereof. In this paper, we tighten the gap between the upper and lower bounds for the studied classes and establish worst-case optimality for some fragments of the considered classes. We also debunk a well-believed conjecture about which query-related quantity, in the worst-case, optimally captures the communication complexity of the studied problem.
Cite as
Heba Aamer, Xiao Hu, and Bas Ketsman. Neither Cover nor Pack: Distributed Worst-Case Optimality of Degree-2 Joins. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 8:1-8:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{aamer_et_al:LIPIcs.ICDT.2026.8,
author = {Aamer, Heba and Hu, Xiao and Ketsman, Bas},
title = {{Neither Cover nor Pack: Distributed Worst-Case Optimality of Degree-2 Joins}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {8:1--8:20},
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.2026.8},
URN = {urn:nbn:de:0030-drops-256226},
doi = {10.4230/LIPIcs.ICDT.2026.8},
annote = {Keywords: degree-two joins, worst-case optimality, distributed algorithms}
}
Document
Acyclic Join Sampling Under Selections: Dichotomy, Union Sampling, and Enumeration
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
Bounding the Makespan of Transaction Schedules
Abstract
The performance of transactional database systems is typically evaluated by measuring the amount of transactions they can commit to the database per second. However, fairly measuring this for the same workload on different systems is not trivial. It is therefore relevant to formalize schedule efficiency, investigate the space of all possible efficient schedules, and identify whether there is any room for improvement. Prior transaction theory largely centers on decision problems relating to safety, such as the serializability, robustness, and allocation problems. Most pertinently, these problems take already scheduled transactions as input, and do not directly consider the efficiency of those schedules.
In this work, we define schedules as assignments of operations on objects to discrete points in time. This allows us to quantify efficiency as the elapsed duration between the schedule’s beginning and end, more commonly known as the makespan in the scheduling literature. We establish that, given some set of transactions and a desired makespan, it is NP-complete to decide if there exists a conflict serializable schedule which is bounded by that makespan. We additionally provide an instance optimal algorithm for scheduling transaction sets with a single contention point, that is, exactly one object may appear in conflicting operations. Lastly, we give worst-case optimal bounds on the makespan, meaning that schedules can never exceed this bound, and for the worst transaction sets, the bound is optimal.
Cite as
Tim Baccaert, Brecht Vandevoort, and Bas Ketsman. Bounding the Makespan of Transaction Schedules. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 10:1-10:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{baccaert_et_al:LIPIcs.ICDT.2026.10,
author = {Baccaert, Tim and Vandevoort, Brecht and Ketsman, Bas},
title = {{Bounding the Makespan of Transaction Schedules}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {10:1--10:20},
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.2026.10},
URN = {urn:nbn:de:0030-drops-256242},
doi = {10.4230/LIPIcs.ICDT.2026.10},
annote = {Keywords: Transactions, Scheduling, Discrete Optimization, Complexity}
}
Document
Factorised Representations of Join Queries: Tight Bounds and a New Dichotomy
Abstract
A common theme in factorised databases and knowledge compilation is the representation of solution sets in a useful yet succinct data structure. In this paper, we study the representation of the result of join queries (or, equivalently, the set of homomorphisms between two relational structures). We focus on the very general format of {∪,×}-circuits - also known as d-representations or DNNF circuits - and aim to find the limits of this approach.
In prior work, it has been shown that there always exists a {∪,×}-circuit of size N^O(subw) representing the query result, where N is the size of the database and subw the submodular width of the query. If the arity of all relations is bounded by a constant, then subw is linear in the treewidth tw of the query. In this setting, the authors of this paper proved a lower bound of N^Ω(tw^ε) on the circuit size (ICALP 2023), where ε > 0 depends on the excluded grid theorem.
Our first main contribution is to improve this lower bound to N^Ω(tw), which is tight up to a constant factor in the exponent. Our second contribution is a N^Ω(subw^{1/4}) lower bound on the circuit size for join queries over relations of unbounded arity. Both lower bounds are unconditional lower bounds on the circuit size for well-chosen database instances. Their proofs use a combination of structural (hyper)graph theory with communication complexity in a simple yet novel way. While the second lower bound is asymptotically equivalent to Marx’s conditional bound on the decision complexity (JACM 2013), our N^Θ(tw) bound in the bounded arity setting is tight, while the best conditional bound on the decision complexity is N^Ω(tw/log tw). Note that removing this logarithmic factor in the decision setting is a major open problem.
Cite as
Christoph Berkholz and Harry Vinall-Smeeth. Factorised Representations of Join Queries: Tight Bounds and a New Dichotomy. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 11:1-11:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{berkholz_et_al:LIPIcs.ICDT.2026.11,
author = {Berkholz, Christoph and Vinall-Smeeth, Harry},
title = {{Factorised Representations of Join Queries: Tight Bounds and a New Dichotomy}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {11:1--11:20},
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.2026.11},
URN = {urn:nbn:de:0030-drops-256255},
doi = {10.4230/LIPIcs.ICDT.2026.11},
annote = {Keywords: join queries, homomorphisms, factorised databases, succinct representation, knowledge compilation, lower bounds}
}
Document
The Complexity of Finding Missing Answer Repairs
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
Complexity of Evaluating GQL Queries
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
Lower Bounds for the Algorithmic Complexity of Learned Indexes
Abstract
Learned index structures aim to accelerate queries by training machine learning models to approximate the rank function associated with a database attribute. While effective in practice, their theoretical limitations are not fully understood. We present a framework for proving lower bounds on query time for learned indexes, expressed in terms of their space overhead and parameterized by the model class used for approximation. Our formulation captures a broad family of one-dimensional learned indexes, including most existing designs, as piecewise model-based predictors.
We solve the problem of lower bounding query time in two steps: first, we use probabilistic tools to control the effect of sampling when the database attribute is drawn from a probability distribution. Then, we analyze the approximation-theoretic problem of how to optimally represent a cumulative distribution function with approximators from a given model class. Within this framework, we derive lower bounds under a range of modeling and distributional assumptions, paying particular attention to the case of piecewise linear and piecewise constant model classes, which are common in practical implementations.
Our analysis shows how tools from approximation theory, such as quantization and Kolmogorov widths, can be leveraged to formalize the space-time trade-offs inherent to learned index structures. The resulting bounds illuminate core limitations of these methods.
Cite as
Luis Alberto Croquevielle, Roman Sokolovskii, and Thomas Heinis. Lower Bounds for the Algorithmic Complexity of Learned Indexes. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 14:1-14:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{croquevielle_et_al:LIPIcs.ICDT.2026.14,
author = {Croquevielle, Luis Alberto and Sokolovskii, Roman and Heinis, Thomas},
title = {{Lower Bounds for the Algorithmic Complexity of Learned Indexes}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {14:1--14:21},
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.2026.14},
URN = {urn:nbn:de:0030-drops-256285},
doi = {10.4230/LIPIcs.ICDT.2026.14},
annote = {Keywords: Learned Indexes, Stochastic Processes, Approximation Theory}
}
Document
A Formal Query Language and Automata Model for Aggregation in Complex Event Recognition
Abstract
Complex Event Recognition (CER) systems are used to identify complex patterns in event streams, such as those found in stock markets, sensor networks, and other similar applications. An important task in such patterns is aggregation, which involves summarizing a set of values into a single value using an algebraic function, such as the maximum, sum, or average, among others. Despite the relevance of this task, query languages in CER typically support aggregation in a restricted syntactic form, and their semantics are generally undefined.
In this work, we present a first step toward formalizing a query language with aggregation for CER. We propose to extend Complex Event Logic (CEL), a formal query language for CER, with aggregation operations. This task requires revisiting the semantics of CEL, using a new semantics based on bags of tuples instead of sets of positions. Then, we present an extension of CEL, called Aggregation CEL (ACEL), which introduces an aggregation operator for any commutative monoid operation. The operator can be freely composed with previous CEL operators, allowing users to define complex queries and patterns. We showcase several queries in practice where ACEL proves to be natural for specifying them. From the computational side, we present a novel automata model, called Aggregation Complex Event Automata (ACEA), that extends the previous proposal of Complex Event Automata (CEA) with aggregation and filtering features. Moreover, we demonstrate that every query in ACEL can be expressed in ACEA, illustrating the effectiveness of our computational model. Finally, we study the expressiveness of ACEA through the lens of ACEL, showing that the automata model is more expressive than ACEL.
Cite as
Pierre Bourhis, Cristian Riveros, and Amaranta Salas. A Formal Query Language and Automata Model for Aggregation in Complex Event Recognition. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 15:1-15:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{bourhis_et_al:LIPIcs.ICDT.2026.15,
author = {Bourhis, Pierre and Riveros, Cristian and Salas, Amaranta},
title = {{A Formal Query Language and Automata Model for Aggregation in Complex Event Recognition}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {15:1--15:20},
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.2026.15},
URN = {urn:nbn:de:0030-drops-256291},
doi = {10.4230/LIPIcs.ICDT.2026.15},
annote = {Keywords: Streams, complex event recognition, query language, aggregation}
}
Document
Gamma Acyclicity, Annotated Relations, and Consistency Witness Functions
Abstract
During the early days of relational database theory it was realized that "acyclic" database schemas possess a number of desirable properties. In fact, three different notions of "acyclicity" were identified and investigated during the 1980s, namely, α-acyclicity, β-acyclicity, and γ-acyclicity. Much more recently, the study of α-acyclicity was extended to annotated relations, where the annotations are values from some positive commutative monoid. The recent results about α-acyclic schemas and annotated relations give rise to results about β-acyclic schemas and annotated relations, since a schema is β-acyclic if and only if every sub-schema of it is α-acyclic. Here, we study γ-acyclic schemas and annotated relations. Our main finding is that the characterization of γ-acyclic schemas in terms of monotone sequential join expression extends to annotated relations, provided the annotations come from a positive commutative monoid that has the inner consistency property. Furthermore, the results reported here shed light on the role of the join of two standard relations. Specifically, our results reveal that the only relevant property of the join of two standard relations is that it is a witness to the consistency of the two relations, provided that these two relations are consistent. For the more abstract setting of annotated relations, this property of the standard join is captured by the notion of a consistency witness function, a notion which we systematically utilize in this work.
Cite as
Albert Atserias and Phokion G. Kolaitis. Gamma Acyclicity, Annotated Relations, and Consistency Witness Functions. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 16:1-16:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{atserias_et_al:LIPIcs.ICDT.2026.16,
author = {Atserias, Albert and Kolaitis, Phokion G.},
title = {{Gamma Acyclicity, Annotated Relations, and Consistency Witness Functions}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {16:1--16:18},
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.2026.16},
URN = {urn:nbn:de:0030-drops-256304},
doi = {10.4230/LIPIcs.ICDT.2026.16},
annote = {Keywords: annotated relations, gamma-acyclicity, consistency witness functions}
}
Document
Algorithms for Optimizing Acyclic Queries
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
Output-Sensitive Evaluation of Acyclic Conjunctive Regular Path Queries
Abstract
Conjunctive Regular Path Queries, or CRPQs for short, are an essential construct in graph query languages. In this paper, we propose the first output-sensitive algorithm for evaluating acyclic CRPQs. It is output-sensitive in the sense that its complexity is a function of the sizes of the input graph and of the query output and not of the output sizes of the regular expressions that appear in the query, as these latter sizes can be larger than the query output size.
Our algorithm proceeds in two stages. In the first stage, it contracts the given query into a free-connex acyclic one such that the output of the original query can be obtained from the output of the contracted one. This contraction removes bound variables by composing regular expressions or by promoting bound variables to free ones. The minimum necessary number of promoted bound variables gives the contraction width, which is a novel parameter specific to CRPQs. In the second stage, our algorithm evaluates the free-connex acyclic CRPQ and projects away the columns of the promoted bound variables. It ensures output-sensitivity by computing the calibrated outputs of the regular expressions appearing in the free-connex acyclic CRPQ in time proportional to their sizes.
Our algorithm has lower complexity than the state-of-the-art approaches for problem instances where the query output is asymptotically smaller than the output sizes of the regular expressions that appear in the query.
Cite as
Mahmoud Abo Khamis, Alexandru-Mihai Hurjui, Ahmet Kara, Dan Olteanu, Dan Suciu, and Zilu Tian. Output-Sensitive Evaluation of Acyclic Conjunctive Regular Path Queries. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 18:1-18:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{abokhamis_et_al:LIPIcs.ICDT.2026.18,
author = {Abo Khamis, Mahmoud and Hurjui, Alexandru-Mihai and Kara, Ahmet and Olteanu, Dan and Suciu, Dan and Tian, Zilu},
title = {{Output-Sensitive Evaluation of Acyclic Conjunctive Regular Path Queries}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {18:1--18:20},
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.2026.18},
URN = {urn:nbn:de:0030-drops-256321},
doi = {10.4230/LIPIcs.ICDT.2026.18},
annote = {Keywords: graph databases, regular path queries, output-sensitive algorithms}
}
Document
Dynamic Necklace Splitting
Abstract
The necklace splitting problem is a classic problem in fair division with many applications, including data-informed fair hash maps. We extend necklace splitting to a dynamic setting, allowing for relocation, insertion, and deletion of beads. We present linear-time, optimal algorithms for the two-color case that support all dynamic updates. For more than two colors, we give linear-time, optimal algorithms for relocation subject to a restriction on the number of agents. Finally, we propose a randomized algorithm for the two-color case that handles all dynamic updates, guarantees approximate fairness with high probability, and runs in polylogarithmic time when the number of agents is small.
Cite as
Rishi Advani, Abolfazl Asudeh, Mohsen Dehghankar, and Stavros Sintos. Dynamic Necklace Splitting. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 19:1-19:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{advani_et_al:LIPIcs.ICDT.2026.19,
author = {Advani, Rishi and Asudeh, Abolfazl and Dehghankar, Mohsen and Sintos, Stavros},
title = {{Dynamic Necklace Splitting}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {19:1--19:20},
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.2026.19},
URN = {urn:nbn:de:0030-drops-256332},
doi = {10.4230/LIPIcs.ICDT.2026.19},
annote = {Keywords: Necklace splitting, dynamic algorithms, fair division}
}
Document
Responsibility Measures for Conjunctive Queries with Negation
Abstract
We contribute to the recent line of work on responsibility measures that quantify the contributions of database facts to obtaining a query result. In contrast to existing work which has almost exclusively focused on monotone queries, here we explore how to define responsibility measures for unions of conjunctive queries with negated atoms (UCQ^¬s). After first investigating the question of what constitutes a reasonable notion of qualitative explanation or relevance for queries with negated atoms, we propose two approaches, one assigning scores to (positive) database facts and the other also considering negated facts. Our approaches, which are orthogonal to the previously studied score of Reshef et al. [Alon Reshef et al., 2020], can be used to lift previously studied scores for monotone queries, known as drastic Shapley and weighted sums of minimal supports (WSMS), to UCQ^¬s. We investigate the data and combined complexity of the resulting measures, notably showing that the WSMS measures are tractable in data complexity for all UCQ^¬s and further establishing tractability in combined complexity for suitable classes of conjunctive queries with negation.
Cite as
Meghyn Bienvenu, Diego Figueira, and Pierre Lafourcade. Responsibility Measures for Conjunctive Queries with Negation. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 20:1-20:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{bienvenu_et_al:LIPIcs.ICDT.2026.20,
author = {Bienvenu, Meghyn and Figueira, Diego and Lafourcade, Pierre},
title = {{Responsibility Measures for Conjunctive Queries with Negation}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {20:1--20:20},
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.2026.20},
URN = {urn:nbn:de:0030-drops-256340},
doi = {10.4230/LIPIcs.ICDT.2026.20},
annote = {Keywords: query responsibility measures, conjunctive queries with negation, non-monotone queries, Shapley value, explainability, weighted sums of minimal supports (WSMS)}
}
Document
First-Order Rewritability of Rule-Based Ontology Mediated Queries with Negation
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
View-Based Query Determinacy for Walk-Based Semantics
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
Conjunctive Query Containment with Safe Negation and TGD One-Boundedness
Abstract
Query containment is a fundamental database problem which has been extensively studied for conjunctive queries (CQs). The most famous result is arguably the Homomorphism Theorem: a CQ q₁ is contained in a CQ q₂ iff there is a homomorphism from q₂ to q₁. However, when extending conjunctive queries with safe base negation (CQ^¬), this test becomes incomplete, hence, requiring significantly more expensive procedures due to its inherently harder complexity (Π₂^P-hard).
In this paper, we define and study the classes CQ^{1¬}_{HT} and CQ^{¬}_{HT}: the classes of conjunctive queries extended with one or several safe negated atoms that satisfy the Homomorphism Theorem, and hence, whose containment check is in NP. To characterise them, we define what we call the dependency-version of a query, which is a dependency that, intuitively, models the databases in which the query is false. It turns out that, when the query q contains one (several) negated atom(s), the query satisfies the Homomorphism Theorem iff its tgd(ded)-version is uniformly one-bounded. We also show that CQ^¬_{HT} membership is EXPTIME-hard, but its complexity reduces to Π₂^P in the CQ^{1¬}_{HT} case, and to NP when bounding the number of positive atoms that can unify with the negated one.
Cite as
Xavier Oriol. Conjunctive Query Containment with Safe Negation and TGD One-Boundedness. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 23:1-23:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{oriol:LIPIcs.ICDT.2026.23,
author = {Oriol, Xavier},
title = {{Conjunctive Query Containment with Safe Negation and TGD One-Boundedness}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {23:1--23:20},
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.2026.23},
URN = {urn:nbn:de:0030-drops-256373},
doi = {10.4230/LIPIcs.ICDT.2026.23},
annote = {Keywords: conjunctive queries, query containment, safe negation, tgd, one-boundedness}
}
Document
Database Theory in Action
Database Theory in Action: Evaluation of Aggregate Queries Without Materialisation
Abstract
Aggregate queries often require computing large intermediate joins despite producing only small outputs. We identify broad classes of acyclic aggregate queries that can be evaluated without materialising any join results, using a bottom-up, semi-join–based propagation of cardinalities and partial aggregates. An implementation in Spark SQL shows that this approach is widely applicable and yields substantial performance gains on standard benchmarks.
Cite as
Matthias Lanzinger, Reinhard Pichler, and Alexander Selzer. Database Theory in Action: Evaluation of Aggregate Queries Without Materialisation. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 24:1-24:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{lanzinger_et_al:LIPIcs.ICDT.2026.24,
author = {Lanzinger, Matthias and Pichler, Reinhard and Selzer, Alexander},
title = {{Database Theory in Action: Evaluation of Aggregate Queries Without Materialisation}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {24:1--24:5},
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.2026.24},
URN = {urn:nbn:de:0030-drops-256380},
doi = {10.4230/LIPIcs.ICDT.2026.24},
annote = {Keywords: Join Processing, Aggregate Queries, Acyclic Conjunctive Queries}
}
Document
Database Theory in Action
Database Theory in Action: Yannakakis' Algorithm
Abstract
Yannakakis' seminal algorithm is optimal for acyclic joins, yet it has not been widely adopted due to its poor performance in practice. This paper briefly surveys recent advancements in making Yannakakis' algorithm more practical, in terms of both efficiency and ease of implementation, and points out several avenues for future research.
Cite as
Paraschos Koutris, Stijn Vansummeren, Qichen Wang, Yisu Remy Wang, and Xiangyao Yu. Database Theory in Action: Yannakakis' Algorithm. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 25:1-25:6, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{koutris_et_al:LIPIcs.ICDT.2026.25,
author = {Koutris, Paraschos and Vansummeren, Stijn and Wang, Qichen and Wang, Yisu Remy and Yu, Xiangyao},
title = {{Database Theory in Action: Yannakakis' Algorithm}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {25:1--25:6},
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.2026.25},
URN = {urn:nbn:de:0030-drops-256395},
doi = {10.4230/LIPIcs.ICDT.2026.25},
annote = {Keywords: Join algorithms, acyclicity, Yannakakis' algorithm}
}
Document
Database Theory in Action
Database Theory in Action: From Inexpressibility to Efficiency in GQL’s Order-Constrained Paths
Abstract
Pattern matching of core GQL, the new ISO standard for querying property graphs, cannot check whether edge values are increasing along a path, as established in recent work. We present a constructive translation that overcomes this limitation by compiling the increasing-edges condition into the input graph. Remarkably, the benefit of this construction goes beyond restoring expressiveness. In our proof-of-concept implementation in Neo4j’s Cypher, where such path constraints are expressible but costly, our compiled version runs faster and avoids timeouts. This illustrates how a theoretically motivated translation can not only close an expressiveness gap but also bring practical performance gains.
Cite as
Hadar Rotschield and Liat Peterfreund. Database Theory in Action: From Inexpressibility to Efficiency in GQL’s Order-Constrained Paths. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 26:1-26:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{rotschield_et_al:LIPIcs.ICDT.2026.26,
author = {Rotschield, Hadar and Peterfreund, Liat},
title = {{Database Theory in Action: From Inexpressibility to Efficiency in GQL’s Order-Constrained Paths}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {26:1--26:5},
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.2026.26},
URN = {urn:nbn:de:0030-drops-256408},
doi = {10.4230/LIPIcs.ICDT.2026.26},
annote = {Keywords: Property graphs, ISO GQL, Graph Query Languages, Pattern Matching}
}
Document
Database Theory in Action
Database Theory in Action: Direct Access to Query Answers
Abstract
Direct access asks for the retrieval of query answers by their ranked position, given a query and a desired order. While the time complexity of data structures supporting such accesses has been studied in depth, and efficient algorithms for many queries and common orders are known, their practical performance has received little attention. We provide an implementation covering a wide range of queries and orders; it allows us to investigate intriguing practical aspects, including the comparative performance of database systems and the relationship between direct access and its single-access counterpart.
Cite as
Jiayin Hu and Nikolaos Tziavelis. Database Theory in Action: Direct Access to Query Answers. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 27:1-27:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)
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@InProceedings{hu_et_al:LIPIcs.ICDT.2026.27,
author = {Hu, Jiayin and Tziavelis, Nikolaos},
title = {{Database Theory in Action: Direct Access to Query Answers}},
booktitle = {29th International Conference on Database Theory (ICDT 2026)},
pages = {27:1--27:5},
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.2026.27},
URN = {urn:nbn:de:0030-drops-256411},
doi = {10.4230/LIPIcs.ICDT.2026.27},
annote = {Keywords: direct access, conjunctive queries, joins, ranking}
}
Document
Database Theory in Action
Database Theory in Action: Learning Logical Modelling with Iltis
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}
}