8,244 research outputs found
Устройство для автоматического включения резервного электронасоса двухстороннего действия
Ontology-mediated query answering is an extensively
studied paradigm, which aims at improving
query answers with the use of a logical theory. As a
form of logical entailment, ontology-mediated query
answering is fully interpretable, which makes it possible
to derive explanations for query answers. Surprisingly,
however, explaining answers for ontologymediated
queries has received little attention for
ontology languages based on existential rules. In
this paper, we close this gap, and study the problem
of explaining query answers in terms of minimal
subsets of database facts. We provide a thorough
complexity analysis for several decision problems
associated with minimal explanations under existential
rules.Alan Turing InstituteEPSR
Query Answer Explanations under Existential Rules
Ontology-mediated query answering is an extensively studied paradigm, which aims at improving
query answers with the use of a logical theory. In this paper, we focus on ontology languages based on
existential rules, and we carry out a thorough complexity analysis of the problem of explaining query
answers in terms of minimal subsets of database facts and related task
On abduction and answer generation through constrained resolution
Recently, extensions of constrained logic programming and constrained resolution for theorem proving have been introduced, that consider constraints, which are interpreted under an open world assumption. We discuss relationships between applications of these approaches for query answering in knowledge base systems on the one hand and abduction-based hypothetical reasoning on the other hand. We show both that constrained resolution can be used as an operationalization of (some limited form of) abduction and that abduction is the logical status of an answer generation process through constrained resolution, ie., it is an abductive but not a deductive form of reasoning
Complexity of Inconsistency-Tolerant Query Answering in Datalog+/- under Cardinality-Based Repairs
Querying inconsistent ontological knowledge bases is an important problem in practice, for which
several inconsistency-tolerant semantics have been proposed. In these semantics, the input database is
erroneous, and a repair is a maximally consistent database subset. Different notions of maximality (such
as subset and cardinality maximality) have been considered. In this paper, we give a precise picture of
the computational complexity of inconsistency-tolerant query answering in a wide range of Datalog+/–
languages under the cardinality-based versions of three prominent repair semantic
Query-Answer Causality in Databases: Abductive Diagnosis and View-Updates
Causality has been recently introduced in databases, to model, characterize
and possibly compute causes for query results (answers). Connections between
query causality and consistency-based diagnosis and database repairs (wrt.
integrity constrain violations) have been established in the literature. In
this work we establish connections between query causality and abductive
diagnosis and the view-update problem. The unveiled relationships allow us to
obtain new complexity results for query causality -the main focus of our work-
and also for the two other areas.Comment: To appear in Proc. UAI Causal Inference Workshop, 2015. One example
was fixe
Querying Data Exchange Settings Beyond Positive Queries
Data exchange, the problem of transferring data from a source schema to a
target schema, has been studied for several years.
The semantics of answering positive queries over the target schema has been
defined in early work, but little attention has been paid to more general
queries. A few proposals of semantics for more general queries exist but they
either do not properly extend the standard semantics under positive queries,
giving rise to counterintuitive answers, or they make query answering
undecidable even for the most important data exchange settings, e.g., with
weakly-acyclic dependencies.
The goal of this paper is to provide a new semantics for data exchange that
is able to deal with general queries. At the same time, we want our semantics
to coincide with the classical one when focusing on positive queries, and to
not trade-off too much in terms of complexity of query answering. We show that
query answering is undecidable in general under the new semantics, but it is
\co\NP\complete when the dependencies are weakly-acyclic.
Moreover, in the latter case, we show that exact answers under our semantics
can be computed by means of logic programs with choice, thus exploiting
existing efficient systems. For more efficient computations, we also show that
our semantics allows for the construction of a representative target instance,
similar in spirit to a universal solution, that can be exploited for computing
approximate answers in polynomial time. Under consideration in Theory and
Practice of Logic Programming (TPLP).Comment: Under consideration in Theory and Practice of Logic Programming
(TPLP
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