110 research outputs found
Query-based comparison of OBDA specifications
An ontology-based data access (OBDA) system is composed of one or more data sources, an ontology that provides a conceptual view of the data, and declarative mappings that relate the data and ontology schemas. In order to debug and optimize such systems, it is important to be able to analyze and compare OBDA specifications. Recent work in this direction compared specifications using classical notions of equivalence and entailment, but an interesting alternative is to consider query-based notions, in which two specifications are deemed equivalent if they give the same answers to the considered query or class of queries for all possible data sources. In this paper, we define such query-based notions of entailment and equivalence of OBDA specifications and investigate the complexity of the resulting analysis tasks when the ontology is formulated in DL-LiteR
Inconsistency Handling in Ontology-Mediated Query Answering: A Progress Report
International audienceThis paper accompanies an invited talk on inconsistency handling in OMQA and presents a concise summary of the research that has been conducted in the area
Tree-like Queries in OWL 2 QL: Succinctness and Complexity Results
This paper investigates the impact of query topology on the difficulty of
answering conjunctive queries in the presence of OWL 2 QL ontologies. Our first
contribution is to clarify the worst-case size of positive existential (PE),
non-recursive Datalog (NDL), and first-order (FO) rewritings for various
classes of tree-like conjunctive queries, ranging from linear queries to
bounded treewidth queries. Perhaps our most surprising result is a
superpolynomial lower bound on the size of PE-rewritings that holds already for
linear queries and ontologies of depth 2. More positively, we show that
polynomial-size NDL-rewritings always exist for tree-shaped queries with a
bounded number of leaves (and arbitrary ontologies), and for bounded treewidth
queries paired with bounded depth ontologies. For FO-rewritings, we equate the
existence of polysize rewritings with well-known problems in Boolean circuit
complexity. As our second contribution, we analyze the computational complexity
of query answering and establish tractability results (either NL- or
LOGCFL-completeness) for a range of query-ontology pairs. Combining our new
results with those from the literature yields a complete picture of the
succinctness and complexity landscapes for the considered classes of queries
and ontologies.Comment: This is an extended version of a paper accepted at LICS'15. It
contains both succinctness and complexity results and adopts FOL notation.
The appendix contains proofs that had to be omitted from the conference
version for lack of space. The previous arxiv version (a long version of our
DL'14 workshop paper) only contained the succinctness results and used
description logic notatio
Inconsistency Handling in Prioritized Databases with Universal Constraints: Complexity Analysis and Links with Active Integrity Constraints
This paper revisits the problem of repairing and querying inconsistent
databases equipped with universal constraints. We adopt symmetric difference
repairs, in which both deletions and additions of facts can be used to restore
consistency, and suppose that preferred repair actions are specified via a
binary priority relation over (negated) facts. Our first contribution is to
show how existing notions of optimal repairs, defined for simpler denial
constraints and repairs solely based on fact deletion, can be suitably extended
to our richer setting. We next study the computational properties of the
resulting repair notions, in particular, the data complexity of repair checking
and inconsistency-tolerant query answering. Finally, we clarify the
relationship between optimal repairs of prioritized databases and repair
notions introduced in the framework of active integrity constraints. In
particular, we show that Pareto-optimal repairs in our setting correspond to
founded, grounded and justified repairs w.r.t. the active integrity constraints
obtained by translating the prioritized database. Our study also yields useful
insights into the behavior of active integrity constraints.Comment: This is an extended version of a paper appearing at the 20th
International Conference on Principles of Knowledge Representation and
Reasoning (KR 2023). 28 page
Querying and Repairing Inconsistent Prioritized Knowledge Bases: Complexity Analysis and Links with Abstract Argumentation
In this paper, we explore the issue of inconsistency handling over
prioritized knowledge bases (KBs), which consist of an ontology, a set of
facts, and a priority relation between conflicting facts. In the database
setting, a closely related scenario has been studied and led to the definition
of three different notions of optimal repairs (global, Pareto, and completion)
of a prioritized inconsistent database. After transferring the notions of
globally-, Pareto- and completion-optimal repairs to our setting, we study the
data complexity of the core reasoning tasks: query entailment under
inconsistency-tolerant semantics based upon optimal repairs, existence of a
unique optimal repair, and enumeration of all optimal repairs. Our results
provide a nearly complete picture of the data complexity of these tasks for
ontologies formulated in common DL-Lite dialects. The second contribution of
our work is to clarify the relationship between optimal repairs and different
notions of extensions for (set-based) argumentation frameworks. Among our
results, we show that Pareto-optimal repairs correspond precisely to stable
extensions (and often also to preferred extensions), and we propose a novel
semantics for prioritized KBs which is inspired by grounded extensions and
enjoys favourable computational properties. Our study also yields some results
of independent interest concerning preference-based argumentation frameworks.Comment: 27 pages. To appear in the 17th International Conference on
Principles of Knowledge Representation and Reasoning (KR 2020) without the
appendi
Towards a Unified View of AI Planning and Reactive Synthesis
International audienceAutomated planning and reactive synthesis are well-established techniques for sequential decision making. In this paper we examine a collection of AI planning problems with temporally extended goals, specified in Linear Temporal Logic (LTL). We characterize these so-called LTL planning problems as two-player games and thereby establish their correspondence to reactive synthesis problems. This unifying view furthers our understanding of the relationship between plan and program synthesis, establishing complexity results for LTL planning tasks. Building on this correspondence, we identify restricted fragments of LTL for which plan synthesis can be realized more efficiently
Nested Regular Path Queries in Description Logics
Two-way regular path queries (2RPQs) have received increased attention
recently due to their ability to relate pairs of objects by flexibly navigating
graph-structured data. They are present in property paths in SPARQL 1.1, the
new standard RDF query language, and in the XML query language XPath. In line
with XPath, we consider the extension of 2RPQs with nesting, which allows one
to require that objects along a path satisfy complex conditions, in turn
expressed through (nested) 2RPQs. We study the computational complexity of
answering nested 2RPQs and conjunctions thereof (CN2RPQs) in the presence of
domain knowledge expressed in description logics (DLs). We establish tight
complexity bounds in data and combined complexity for a variety of DLs, ranging
from lightweight DLs (DL-Lite, EL) up to highly expressive ones. Interestingly,
we are able to show that adding nesting to (C)2RPQs does not affect worst-case
data complexity of query answering for any of the considered DLs. However, in
the case of lightweight DLs, adding nesting to 2RPQs leads to a surprising jump
in combined complexity, from P-complete to Exp-complete.Comment: added Figure
- âŠ