scholarly journals Query answering in circumscribed OWL2 profiles

2021 ◽  
Author(s):  
Piero A. Bonatti
Keyword(s):  
Description Logics ◽  
Knowledge Bases ◽  
Query Answering ◽  
Data Complexity ◽  
Conjunctive Query ◽  
Conjunctive Queries

AbstractThis paper partially bridges a gap in the literature on Circumscription in Description Logics by investigating the tractability of conjunctive query answering in OWL2’s profiles. It turns out that the data complexity of conjunctive query answering is coNP-hard in circumscribed $\mathcal {E}{\mathscr{L}}$ E L and DL-lite, while in circumscribed OWL2-RL conjunctive queries retain their classical semantics. In an attempt to capture nonclassical inferences in OWL2-RL, we consider conjunctive queries with safe negation. They can detect some of the nonclassical consequences of circumscribed knowledge bases, but data complexity becomes coNP-hard. In circumscribed $\mathcal {E}{\mathscr{L}}$ E L , answering queries with safe negation is undecidable.

scholarly journals Conjunctive Query Answering for the Description Logic SHIQ

2008 ◽  
Vol 31 ◽  
pp. 157-204 ◽  
Author(s):  
B. Glimm ◽  
C. Lutz ◽  
I. Horrocks ◽  
U. Sattler
Keyword(s):  
Description Logic ◽  
Query Language ◽  
Description Logics ◽  
Knowledge Bases ◽  
Deterministic Algorithm ◽  
Query Answering ◽  
Conjunctive Query ◽  
Conjunctive Queries ◽  
Complexity Bounds ◽  
Double Exponential

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 tight 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 containment in co-NP.

scholarly journals Answering Conjunctive Regular Path Queries over Guarded Existential Rules

2017 ◽  
Author(s):  
Jean-François Baget ◽  
Meghyn Bienvenu ◽  
Marie-Laure Mugnier ◽  
Michael Thomazo
Keyword(s):  
Knowledge Bases ◽  
Query Answering ◽  
Linear Case ◽  
Data Complexity ◽  
Conjunctive Queries ◽  
Regular Path ◽  
Regular Path Queries ◽  
Path Queries

Ontology-mediated query answering is concerned with the problem of answering queries over knowledge bases consisting of a database instance and an ontology. While most work in the area focuses on conjunctive queries, navigational queries are gaining increasing attention. In this paper, we investigate the complexity of answering two-way conjunctive regular path queries (CRPQs) over knowledge bases whose ontology is given by a set of guarded existential rules. We first consider the subclass of linear existential rules and show that CRPQ answering is EXPTIME-complete in combined complexity and NL-complete in data complexity, matching the recently established bounds for answering non-conjunctive RPQs. For guarded rules, we provide a non-trivial reduction to the linear case, which allows us to show that the complexity of CRPQ answering is the same as for plain conjunctive queries, namely, 2EXPTIME-complete in combined complexity and PTIME-complete in data complexity.

Deciding Query Entailment in Fuzzy OWL Lite Ontologies

2011 ◽  
pp. 247-268
Author(s):  
Jingwei Cheng ◽  
Z. M. Ma ◽  
Li Yan
Keyword(s):  
Upper Bound ◽  
Description Logics ◽  
Knowledge Bases ◽  
Data Complexity ◽  
Conjunctive Queries ◽  
Logical Foundations ◽  
Fuzzy Query ◽  
Web Community ◽  
Significant Research ◽  
Ontology Languages

Significant research efforts in the Semantic Web community are recently directed toward the representation and reasoning with fuzzy ontologies. Description logics (DLs) are the logical foundations of standard Web ontology languages. Conjunctive queries are deemed as an expressive reasoning service for DLs. This chapter focuses on fuzzy (threshold) conjunctive queries over knowledge bases encoding in fuzzy DL , the logic counterpart of fuzzy OWL Lite language. It shows decidability of fuzzy query entailment in this setting by providing a corresponding tableau-based algorithm. The chapter shows data complexity for answering fuzzy conjunctive queries in fuzzy is in coNP, as long as only simple roles occur in the query. Regarding combined complexity, this research proves a co3NExpTime upper bound in the size of the knowledge base and the query.

scholarly journals Nominals, Inverses, Counting, and Conjunctive Queries or: Why Infinity is your Friend!

2010 ◽  
Vol 39 ◽  
pp. 429-481 ◽  
Author(s):  
S. Rudolph ◽  
B. Glimm
Keyword(s):  
Knowledge Representation ◽  
Description Logic ◽  
Query Language ◽  
Description Logics ◽  
Knowledge Bases ◽  
Conjunctive Query ◽  
Conjunctive Queries ◽  
Decidability Result ◽  
Wide Range ◽  
Significant Attention

Description Logics are knowledge representation formalisms that provide, for example, the logical underpinning of the W3C OWL standards. Conjunctive queries, the standard query language in databases, have recently gained significant attention as an expressive formalism for querying Description Logic knowledge bases. Several different techniques for deciding conjunctive query entailment are available for a wide range of DLs. Nevertheless, the combination of nominals, inverse roles, and number restrictions in OWL 1 and OWL 2 DL causes unsolvable problems for the techniques hitherto available. We tackle this problem and present a decidability result for entailment of unions of conjunctive queries in the DL ALCHOIQb that contains all three problematic constructors simultaneously. Provided that queries contain only simple roles, our result also shows decidability of entailment of (unions of) conjunctive queries in the logic that underpins OWL 1 DL and we believe that the presented results will pave the way for further progress towards conjunctive query entailment decision procedures for the Description Logics underlying the OWL standards.

An Improved Set-based Reasoner for the Description Logic 𝒟ℒD4,׆

2021 ◽  
Vol 178 (4) ◽  
pp. 315-346
Author(s):  
Domenico Cantone ◽  
Marianna Nicolosi-Asmundo ◽  
Daniele Francesco Santamaria
Keyword(s):  
Semantic Web ◽  
Set Theory ◽  
Description Logic ◽  
Knowledge Bases ◽  
Query Answering ◽  
Conjunctive Query ◽  
Classification Problems ◽  
Previous Version ◽  
Decidable Fragment ◽  
Stratified Set

We present a KE-tableau-based implementation of a reasoner for a decidable fragment of (stratified) set theory expressing the description logic 𝒟ℒ〈4LQSR,×〉(D) (𝒟ℒD4,×, for short). Our application solves the main TBox and ABox reasoning problems for 𝒟ℒD4,×. In particular, it solves the consistency and the classification problems for 𝒟ℒD4,×-knowledge bases represented in set-theoretic terms, and a generalization of the Conjunctive Query Answering problem in which conjunctive queries with variables of three sorts are admitted. The reasoner, which extends and improves a previous version, is implemented in C++. It supports 𝒟ℒD4,×-knowledge bases serialized in the OWL/XML format and it admits also rules expressed in SWRL (Semantic Web Rule Language).

UCQ-Rewritings for disjunctive knowledge and queries with negated atoms

Semantic Web ◽  
2020 ◽  
pp. 1-25
Author(s):  
Enrique Matos Alfonso ◽  
Alexandros Chortaras ◽  
Giorgos Stamou
Keyword(s):  
Incomplete Data ◽  
Knowledge Bases ◽  
Query Answering ◽  
Query Rewriting ◽  
Conjunctive Queries

In this paper, we study the problem of query rewriting for disjunctive existential rules. Query rewriting is a well-known approach for query answering on knowledge bases with incomplete data. We propose a rewriting technique that uses negative constraints and conjunctive queries to remove the disjunctive components of disjunctive existential rules. This process eventually generates new non-disjunctive rules, i.e., existential rules. The generated rules can then be used to produce new rewritings using existing rewriting approaches for existential rules. With the proposed technique we are able to provide complete UCQ-rewritings for union of conjunctive queries with universally quantified negation. We implemented the proposed algorithm in the Completo system and performed experiments that evaluate the viability of the proposed solution.

scholarly journals Revisiting Controlled Query Evaluation in Description Logics

2019 ◽  
Author(s):  
Domenico Lembo ◽  
Riccardo Rosati ◽  
Domenico Fabio Savo
Keyword(s):  
Private Information ◽  
Description Logics ◽  
Study Data ◽  
Query Answering ◽  
Query Evaluation ◽  
Data Complexity ◽  
Complexity Results ◽  
Controlled Query Evaluation ◽  
Consistent Query Answering ◽  
The Relationship

Controlled Query Evaluation (CQE) is a confidentiality-preserving framework in which private information is protected through a policy, and a (optimal) censor guarantees that answers to queries are maximized without violating the policy. CQE has been recently studied in the context of ontologies, where the focus has been mainly on the problem of the existence of an optimal censor. In this paper we instead consider query answering over all possible optimal censors. We study data complexity of this problem for ontologies specified in the Description Logics DL-LiteR and EL_bottom and for variants of the censor language, which is the language used by the censor to enforce the policy. In our investigation we also analyze the relationship between CQE and the problem of Consistent Query Answering (CQA). Some of the complexity results we provide are indeed obtained through mutual reduction between CQE and CQA.

scholarly journals Controlled Query Evaluation in Description Logics Through Instance Indistinguishability

2020 ◽  
Author(s):  
Gianluca Cima ◽  
Domenico Lembo ◽  
Riccardo Rosati ◽  
Domenico Fabio Savo
Keyword(s):  
Description Logics ◽  
Privacy Preserving ◽  
Query Answering ◽  
Query Evaluation ◽  
Data Complexity ◽  
First Order ◽  
Complexity Results ◽  
Controlled Query Evaluation

We study privacy-preserving query answering in Description Logics (DLs). Specifically, we consider the approach of controlled query evaluation (CQE) based on the notion of instance indistinguishability. We derive data complexity results for query answering over DL-LiteR ontologies, through a comparison with an alternative, existing confidentiality-preserving approach to CQE. Finally, we identify a semantically well-founded notion of approximated query answering for CQE, and prove that, for DL-LiteR ontologies, this form of CQE is tractable with respect to data complexity and is first-order rewritable, i.e., it is always reducible to the evaluation of a first-order query over the data instance.

scholarly journals Answering Fuzzy Queries over Fuzzy DL-Lite Ontologies

2022 ◽  
pp. 1-30
Author(s):  
GABRIELLA PASI ◽  
RAFAEL PEÑALOZA
Keyword(s):  
Fuzzy Logic ◽  
Domain Knowledge ◽  
Description Logic ◽  
Classical Case ◽  
Point Of View ◽  
Query Answering ◽  
Data Complexity ◽  
Conjunctive Query ◽  
Triangular Norm ◽  
Mathematical Fuzzy Logic

Abstract A prominent problem in knowledge representation is how to answer queries taking into account also the implicit consequences of an ontology representing domain knowledge. While this problem has been widely studied within the realm of description logic ontologies, it has been surprisingly neglected within the context of vague or imprecise knowledge, particularly from the point of view of mathematical fuzzy logic. In this paper, we study the problem of answering conjunctive queries and threshold queries w.r.t. ontologies in fuzzy DL-Lite. Specifically, we show through a rewriting approach that threshold query answering w.r.t. consistent ontologies remains in ${AC}^{0}$ in data complexity, but that conjunctive query answering is highly dependent on the selected triangular norm, which has an impact on the underlying semantics. For the idempotent Gödel t-norm, we provide an effective method based on a reduction to the classical case.

scholarly journals Inconsistency-Tolerant Ontology-Based Data Access Revisited: Taking Mappings into Account

2018 ◽  
Author(s):  
Meghyn Bienvenu
Keyword(s):  
Detailed Analysis ◽  
Description Logics ◽  
Data Access ◽  
Query Answering ◽  
Symmetric Difference ◽  
Relational Data ◽  
Data Complexity

Inconsistency-tolerant query answering in the presence of ontologies has received considerable attention in recent years. However, existing work assumes that the data is expressed using the vocabulary of the ontology and is therefore not directly applicable to ontology-based data access (OBDA), where relational data is connected to the ontology via mappings. This motivates us to revisit existing results in the wider context of OBDA with mappings. After formalizing the problem, we perform a detailed analysis of the data complexity of inconsistency-tolerant OBDA for ontologies formulated in DL-Lite and other data-tractable description logics, considering three different semantics (AR, IAR, and brave), two notions of repairs (subset and symmetric difference), and two classes of global-as-view (GAV) mappings. We show that adding plain GAV mappings does not affect data complexity, but there is a jump in complexity if mappings with negated atoms are considered.

Sign in / Sign up

Export Citation Format

Share Document