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About 989 papers for “Conjunctive query”

Output-sensitive Conjunctive Query Evaluation

Shaleen Deep, Hangdong Zhao, Austen Z. Fan et al. · Proceedings of the ACM on Management of Data · 2024

Join evaluation is one of the most fundamental operations performed by database systems and arguably the most well-studied problem in the Database community. A staggering number of join algorithms have been developed, and commercial database engines use finely tuned join heuristics that take into account many factors including the selectivity of predicates, memory, IO, etc. However, most of the results have catered to either full join queries or non-full join queries but with degree constraints (such as PK-FK relationships) that makes join evaluation easier. Further, most of the algorithms are also not output-sensitive. In this paper, we present a novel, output-sensitive algorithm for the evaluation of acyclic Conjunctive Queries (CQs) that contain arbitrary free variables. Our result is based on a novel generalization of the Yannakakis algorithm and shows that it is possible to improve the running time guarantee of Yannakakis algorithm by a polynomial factor. Importantly, our algorithmic improvement does not depend on the use of fast matrix multiplication, as a recently proposed algorithm does. The application of our algorithm recovers known prior results and improves on known state-of-the-art results for common queries such as paths and stars. The upper bound is complemented with a matching lower bound for star queries, a restricted subclass of acyclic CQs, and a family of cyclic CQs conditioned on two variants of the k -clique conjecture.

Cited by 2Open access

Verification of Conjunctive-QUery Based . . .

Babak Bagheri Hariri, Diego Calvanese, Riccardo De Masellis, et al. · 2011

We introduce semantic artifacts, which are a mechanism that provides both a semantically rich representation of the information on the domain of interest in terms of an ontology, including the underlying data, and a set of actions to change such information over time. In this paper, the ontology is specified as a DL-Lite TBox together with an ABox that may contain both (known) constants and unknown individuals (labeled nulls, represented as Skolem terms). Actions are specified as sets of conditional effects, where conditions are based on conjunctive queries over the ontology (TBox and ABox), and effects are expressed in terms of new ABoxes. In this setting, which is obviously not finite state, we address the verification of temporal/dynamic properties expressed in µ-calculus. Notably, we show decidability of verification, under a suitable restriction inspired by the notion of acyclicity in data exchange.

Cited by 0

Conjunctive Query Answering for the DL SHIQ Conjunctive Query Answering for the Description Logic SHIQ ∗

Birte Glimm, Ian Horrocks, Ulrike Sattler · 2008

Conjunctive queries play an important role as an expressive query language for Description Logics (DLs). Although modern DLs usually provide for transitive roles, conjunctive query answering over DL knowledge bases is only poorly understood if transitive roles are admitted in the query. In this paper, we consider unions of conjunctive queries over knowledge bases formulated in the prominent DL SHIQ and allow transitive roles in both the query and the knowledge base. We show decidability of query answering in this setting and establish two complexity bounds: regarding combined complexity, we prove that there is a deterministic algorithm for query answering that needs time single exponential in the size of the KB and double exponential in the size of the query, which is optimal. Regarding data complexity, we prove co-NP-completeness. 1.

Cited by 0

Conjunctive Query Answering in Rough EL

Rafael Peñaloza, Veronika Thost, Anni-Yasmin Turhan · 2014

Rough Description Logics have recently been studied as a means for representing and reasoning with imprecise knowledge. Real-world applications need to exploit reasoning over such knowledge in an efficient way. We describe how the combined approach to query answering can be extended to the rough setting. In particular, we extend both the canonical model and the rewriting procedure such that rough queries over rough EL ontologies can be answered by considering this information alone.

Cited by 0Open access

Temporal Conjunctive Query Answering via Rewriting

Lukas Westhofen, Jean Christoph Jung, Daniel Neider · Proceedings of the AAAI Conference on Artificial Intelligence · 2025

Querying temporal data has recently gained traction in several artificial intelligence applications. As operational domains of intelligent agents are constantly being expanded, there is a strong need for representing domain knowledge. This comes in the form of ontologies, which are predominantly expressed in description logics and enrich time-stamped data to temporal knowledge bases. For modeling highly complex system environments, expressive description logics are often the formalism of choice. Querying such temporal knowledge bases is a challenging task, but recently a first practical solution has been put forward. We propose a novel approach to the query answering problem based on two well-known rewriting rules from temporal logic. After a careful theoretical analysis of our algorithm, we show in a practical evaluation on several benchmarks that it outperforms state of the art, sometimes by orders of magnitude. Based on our findings, we also propose a fragment of temporal conjunctive queries which guides users towards well-performing queries.

Cited by 0Open access

Revisiting Conjunctive Query Entailment for S

Yazmín Ibáñez-García, Jean Christoph Jung, Vincent Michielini et al. · Proceedings of the AAAI Conference on Artificial Intelligence · 2026

We clarify the complexity of answering unions of conjunctive queries over knowledge bases formulated in the description logic S, the extension of ALC with transitive roles. Contrary to what existing partial results suggested, we show that the problem is, in fact, 2ExpTime-complete; hardness already holds in the presence of two transitive roles and for Boolean conjunctive queries. We complement this result by showing that the problem remains in coNExpTime when the input query is rooted or is restricted to use at most one transitive role (but may use arbitrarily many non-transitive roles).

Cited by 0Open access

Ranked Enumeration of Conjunctive Query Results

Shaleen Deep, Paraschos Koutris · DROPS (Schloss Dagstuhl – Leibniz Center for Informatics) · 2021

We study the problem of enumerating answers of Conjunctive Queries ranked according to a given ranking function. Our main contribution is a novel algorithm with small preprocessing time, logarithmic delay, and non-trivial space usage during execution. To allow for efficient enumeration, we exploit certain properties of ranking functions that frequently occur in practice. To this end, we introduce the notions of decomposable and compatible (w.r.t. a query decomposition) ranking functions, which allow for partial aggregation of tuple scores in order to efficiently enumerate the output. We complement the algorithmic results with lower bounds that justify why restrictions on the structure of ranking functions are necessary. Our results extend and improve upon a long line of work that has studied ranked enumeration from both a theoretical and practical perspective.

Cited by 13Open access

Revisiting Conjunctive Query Entailment for S

Association for Artificial Intelligence 2026, Jean Christoph Jung, YazminAngélica Ibáñez-García et al. · Underline Science Inc. · 2026

We clarify the complexity of answering unions of conjunctive queries over knowledge bases formulated in the description logic $\mathcal{S}$, the extension of $\mathcal{ALC}$ with transitive roles. Contrary to what existing partial results suggested, we show that the problem is, in fact, 2ExpTime-complete; hardness already holds in the presence of two transitive roles and for Boolean conjunctive queries. We complement this result by showing that the problem remains in coNExpTime when the input query is rooted or is restricted to use at most one transitive role (but may use arbitrarily many non-transitive roles).

Cited by 0Open access

Local transformations and conjunctive-query equivalence

Ronald Fagin, Phokion G. Kolaitis · 2012

Over the past several decades, the study of conjunctive queries has occupied a central place in the theory and practice of database systems. In recent years, conjunctive queries have played a prominent role in the design and use of schema mappings for data integration and data exchange tasks. In this paper, we investigate several different aspects of conjunctive-query equivalence in the context of schema mappings and data exchange.

Cited by 9

Temporal Conjunctive Query Answering via Rewriting

Association for Artificial Intelligence 2025, Christoph Jung, Jean, Neider, Daniel et al. · Underline Science Inc. · 2025

Querying temporal data has recently gained traction in several artificial intelligence applications. As operational domains of intelligent agents are constantly being expanded, there is a strong need for representing domain knowledge. This comes in the form of ontologies, which are predominantly expressed in description logics and enrich time-stamped data to temporal knowledge bases. For modeling highly complex system environments, expressive description logics are often the formalism of choice. Querying such temporal knowledge bases is a challenging task, but recently a first practical solution has been put forward. We propose a novel approach to the query answering problem based on two well-known rewriting rules from temporal logic. After a careful theoretical analysis of our algorithm, we show in a practical evaluation on several benchmarks that it outperforms state of the art, sometimes by orders of magnitude. Based on our findings, we also propose a fragment of temporal conjunctive queries which guides users towards well-performing queries.

Cited by 0Open access

The parameterized complexity of conjunctive query . . .

Pamela Harriet Russell · 2005

This thesis is an expository treatment of the article “When is the evaluation of conjunctive queries tractable? ” by Grohe, Schwentick and Segoufin [13]. The topic of the article is the tractability of conjunctive queries to structures. In particular, the authors use a graph-theoretic approach to the study of conjunctive queries; to each query they associate a corresponding graph.

Cited by 0

Faster Conjunctive Query in Temporal Databases

Amin El-Kholy, Barry Richards · 2007

The aim in this paper is to introduce IQ-TREC, a new approach to the task of maintaining and reasoning about temporal databases. We shall address two specific problems in such databases, (1) enforcing consistency (which is equivalent to a restricted form of scheduling) and (2) conjunctive query (which is part of the problem of non-linear plan generation). The key issues concern indefinite temporal data and its relation to resource reasoning. We present both problems as a disjunctive constraint propagation problem. Previous attempts to handle this type of temporal database (TMM and ß- TMM) are presented and discussed. We then specify the IQ-TREC approach to the problem. This approach has been prototyped in the CLP environment ECL i PS e and is now being assessed and used to develop an advanced prototype of the planning system IQ-PLAN.

Cited by 0