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University of Montpellier

Academic institutioneurope · fr
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Research library176linked papers
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Selected work

Representative Papers

Direct Access for Conjunctive Queries with Negation

Oct 24, 2023International Conference on Database Theory

This paper investigates the direct access problem to the k-th answer in lexicographic order for conjunctive queries with negation (CQ¬) over databases: after polynomial-time preprocessing, arbitrary rank-k queries must be answered in polylogarithmic time. To address this, we systematically extend the characterization of direct-access tractability from positive conjunctive queries to CQ¬, introducing a unified framework based on representable relation circuits. We prove that both β-acyclic and bounded nested set-width classes of negative queries are tractable within this framework, strictly generalizing prior tractability boundaries for positive and negative queries. Experimental evaluation confirms that our approach achieves polynomial preprocessing and polylogarithmic access time, subsuming all previously known tractable classes and extending beyond them.

6 citations1 influentialRead paper

Rethinking the Win Ratio: A Causal Framework for Hierarchical Outcome Analysis

Jan 28, 2025

Conventional methods such as the Win Ratio lack a rigorous statistical and causal foundation for quantifying treatment effects in hierarchical multivariate outcomes, potentially leading to erroneous treatment recommendations in heterogeneous populations. Method: We establish, for the first time, a formal causal framework for the Win Ratio—defining identifiable, individual-level causal estimands—and propose a novel estimation procedure based on paired nearest-neighbor matching and doubly robust estimation. Contribution/Results: We prove theoretical consistency and double robustness of the proposed estimator. Extensive validation on synthetic data and the CRASH-3 clinical trial demonstrates substantial improvements in reliability and interpretability of treatment effect estimation. Our work provides both a principled theoretical foundation and a practical methodology for causal inference with complex, hierarchically structured multiple endpoints.

2 citationsRead paper

Model Agnostic Differentially Private Causal Inference

May 26, 2025

Estimating the average treatment effect (ATE) under differential privacy from privacy-sensitive observational data—e.g., healthcare or economic records—faces challenges including strong modeling assumptions, privacy cost scaling with estimator complexity, and limited methodological flexibility. This paper proposes the first general framework that decouples nuisance parameter estimation from privacy protection via folded-splitting and ensemble prediction perturbation. Without assuming a specific data-generating mechanism or parametric model form, it delivers unified differential privacy guarantees for diverse ATE estimators—including G-formula, inverse probability weighting (IPW), and augmented IPW (AIPW). The framework further extends to differentially private meta-analysis of ATEs across multiple private data sources. We establish rigorous differential privacy and statistical efficiency guarantees. Empirical evaluation demonstrates that, under realistic privacy budgets, our method achieves ATE estimation accuracy close to non-private baselines while enabling robust cross-source result integration.

1 citationsRead paper
Recent publications

Latest Papers

A relaxation of the Bermond-Thomassen conjecture

Aug 13, 2026

This study addresses the existence of cycles in the context of the Bermond–Thomassen conjecture for $k \geq 4$. The conjecture posits that every directed graph with minimum out-degree at least $2k - 1$ contains $k$ vertex-disjoint directed cycles. We propose and prove a tight relaxation of this conjecture, establishing that such graphs necessarily contain $k$ vertex-disjoint cycles, each of which is either directed or can be made directed by reversing a single arc. This result resolves an open problem posed by Cames van Batenburg (2021). By integrating structural graph theory with extremal combinatorial methods, we develop a new cycle existence theorem whose bound is best possible, thereby significantly advancing the understanding of this classical conjecture.

0 citationsRead paper

A General Sufficient Condition for Rewriting Horn-ALCHI Atomic Queries into GQL

Aug 05, 2026

This work addresses the problem of efficiently rewriting atomic queries over Horn-ALCHI ontologies into UC2RPQ, a core fragment of the ISO graph query language GQL. To this end, the paper introduces a novel automata-based formal semantics for description logics and incorporates a state stratification condition to eliminate cyclic dependencies. The proposed approach establishes, for the first time, sufficient conditions under which atomic queries over Horn-ALCHI ontologies are rewritable into UC2RPQ. This result substantially extends the applicability of GQL in ontology-mediated querying and provides both a theoretical foundation and a practical pathway for the efficient evaluation of complex ontology-based queries in graph databases.

0 citationsRead paper