Preference-based Inconsistency-Tolerant Query Answering under Existential Rules

2020 ◽  
Author(s):  
Marco Calautti ◽  
Sergio Greco ◽  
Cristian Molinaro ◽  
Irina Trubitsyna
Keyword(s):  
Knowledge Bases ◽  
User Preferences ◽  
Query Answering ◽  
Rule Languages ◽  
Inconsistent Knowledge ◽  
Consistent Subset

Query answering over inconsistent knowledge bases is a problem that has attracted a great deal of interest over the years. Different inconsistency-tolerant semantics have been proposed, and most of them are based on the notion of repair, that is, a "maximal" consistent subset of the database. In general, there can be several repairs, so it is often natural and desirable to express preferences among them. In this paper, we propose a framework for querying inconsistent knowledge bases under user preferences for existential rule languages. We provide generalizations of popular inconsistency-tolerant semantics taking preferences into account and study the data and combined complexity of different relevant problems.

scholarly journals Explanations for Inconsistency-Tolerant Query Answering under Existential Rules

2020 ◽  
Vol 34 (03) ◽  
pp. 2909-2916
Author(s):  
Thomas Lukasiewicz ◽  
Enrico Malizia ◽  
Cristian Molinaro
Keyword(s):  
Knowledge Base ◽  
Complexity Analysis ◽  
Knowledge Bases ◽  
Query Answering ◽  
Complexity Measures ◽  
Rule Languages ◽  
Wide Range ◽  
Inconsistent Knowledge

Querying inconsistent knowledge bases is a problem that has attracted a great deal of interest over the last decades. While several semantics of query answering have been proposed, and their complexity is rather well-understood, little attention has been paid to the problem of explaining query answers. Explainability has recently become a prominent problem in different areas of AI. In particular, explaining query answers allows users to understand not only what is entailed by an inconsistent knowledge base, but also why. In this paper, we address the problem of explaining query answers for existential rules under three popular inconsistency-tolerant semantics, namely, the ABox repair, the intersection of repairs, and the intersection of closed repairs semantics. We provide a thorough complexity analysis for a wide range of existential rule languages and for different complexity measures.

scholarly journals Complexity of Inconsistency-Tolerant Query Answering in Datalog+/– under Cardinality-Based Repairs

2019 ◽  
Vol 33 ◽  
pp. 2962-2969 ◽  
Author(s):  
Thomas Lukasiewicz ◽  
Enrico Malizia ◽  
Andrius Vaicenavičius
Keyword(s):  
Computational Complexity ◽  
Knowledge Bases ◽  
Query Answering ◽  
Conjunctive Query ◽  
Wide Range ◽  
Consistent Subset

Querying inconsistent ontological knowledge bases is an important problem in practice, for which several inconsistencytolerant query answering semantics have been proposed, including query answering relative to all repairs, relative to the intersection of repairs, and relative to the intersection of closed repairs. In these semantics, one assumes that the input database is erroneous, and the notion of repair describes a maximally consistent subset of the input database, where different notions of maximality (such as subset and cardinality maximality) are considered. In this paper, we give a precise picture of the computational complexity of inconsistencytolerant (Boolean conjunctive) query answering in a wide range of Datalog± languages under the cardinality-based versions of the above three repair semantics.

scholarly journals Computing Approximate Query Answers over Inconsistent Knowledge Bases

2018 ◽  
Author(s):  
Sergio Greco ◽  
Cristian Molinaro ◽  
Irina Trubitsyna
Keyword(s):  
Knowledge Base ◽  
Knowledge Bases ◽  
Query Answering ◽  
Compact Representation ◽  
Fine Grained ◽  
Polynomial Time Approximation Algorithm ◽  
Consistent Query Answering ◽  
Approximate Query ◽  
Inconsistent Knowledge ◽  
Consistent Query Answers

Consistent query answering is a principled approach for querying inconsistent knowledge bases. It relies on the notion of a "repair", that is, a maximal consistent subset of the facts in the knowledge base. One drawback of this approach is that entire facts are deleted to resolve inconsistency, even if they may still contain useful "reliable" information. To overcome this limitation, we propose a new notion of repair allowing values within facts to be updated for restoring consistency. This more fine-grained repair primitive allows us to preserve more information in the knowledge base. We also introduce the notion of a "universal repair", which is a compact representation of all repairs. Then, we show that consistent query answering in our framework is intractable (coNP-complete). In light of this result, we develop a polynomial time approximation algorithm for computing a sound (but possibly incomplete) set of consistent query answers.

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).

Query Failure Explanation in Inconsistent Knowledge Bases: A Dialogical Approach

2014 ◽  
pp. 119-133 ◽  
Author(s):  
Abdallah Arioua ◽  
Nouredine Tamani ◽  
Madalina Croitoru ◽  
Patrice Buche
Keyword(s):  
Knowledge Bases ◽  
Dialogical Approach ◽  
Inconsistent Knowledge

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.

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