282 research outputs found
Prioritized Repairing and Consistent Query Answering in Relational Databases
A consistent query answer in an inconsistent database is an answer obtained
in every (minimal) repair. The repairs are obtained by resolving all conflicts
in all possible ways. Often, however, the user is able to provide a preference
on how conflicts should be resolved. We investigate here the framework of
preferred consistent query answers, in which user preferences are used to
narrow down the set of repairs to a set of preferred repairs. We axiomatize
desirable properties of preferred repairs. We present three different families
of preferred repairs and study their mutual relationships. Finally, we
investigate the complexity of preferred repairing and computing preferred
consistent query answers.Comment: Accepted to the special SUM'08 issue of AMA
Exchange-Repairs: Managing Inconsistency in Data Exchange
In a data exchange setting with target constraints, it is often the case that
a given source instance has no solutions. In such cases, the semantics of
target queries trivialize. The aim of this paper is to introduce and explore a
new framework that gives meaningful semantics in such cases by using the notion
of exchange-repairs. Informally, an exchange-repair of a source instance is
another source instance that differs minimally from the first, but has a
solution. Exchange-repairs give rise to a natural notion of exchange-repair
certain answers (XR-certain answers) for target queries. We show that for
schema mappings specified by source-to-target GAV dependencies and target
equality-generating dependencies (egds), the XR-certain answers of a target
conjunctive query can be rewritten as the consistent answers (in the sense of
standard database repairs) of a union of conjunctive queries over the source
schema with respect to a set of egds over the source schema, making it possible
to use a consistent query-answering system to compute XR-certain answers in
data exchange. We then examine the general case of schema mappings specified by
source-to-target GLAV constraints, a weakly acyclic set of target tgds and a
set of target egds. The main result asserts that, for such settings, the
XR-certain answers of conjunctive queries can be rewritten as the certain
answers of a union of conjunctive queries with respect to the stable models of
a disjunctive logic program over a suitable expansion of the source schema.Comment: 29 pages, 13 figures, submitted to the Journal on Data Semantic
An extension of SPARQL for expressing qualitative preferences
In this paper we present SPREFQL, an extension of the SPARQL language that
allows appending a PREFER clause that expresses "soft" preferences over the
query results obtained by the main body of the query. The extension does not
add expressivity and any SPREFQL query can be transformed to an equivalent
standard SPARQL query. However, clearly separating preferences from the "hard"
patterns and filters in the WHERE clause gives queries where the intention of
the client is more cleanly expressed, an advantage for both human readability
and machine optimization. In the paper we formally define the syntax and the
semantics of the extension and we also provide empirical evidence that
optimizations specific to SPREFQL improve run-time efficiency by comparison to
the usually applied optimizations on the equivalent standard SPARQL query.Comment: Accepted to the 2017 International Semantic Web Conference, Vienna,
October 201
A SAT-based System for Consistent Query Answering
An inconsistent database is a database that violates one or more integrity
constraints, such as functional dependencies. Consistent Query Answering is a
rigorous and principled approach to the semantics of queries posed against
inconsistent databases. The consistent answers to a query on an inconsistent
database is the intersection of the answers to the query on every repair, i.e.,
on every consistent database that differs from the given inconsistent one in a
minimal way. Computing the consistent answers of a fixed conjunctive query on a
given inconsistent database can be a coNP-hard problem, even though every fixed
conjunctive query is efficiently computable on a given consistent database.
We designed, implemented, and evaluated CAvSAT, a SAT-based system for
consistent query answering. CAvSAT leverages a set of natural reductions from
the complement of consistent query answering to SAT and to Weighted MaxSAT. The
system is capable of handling unions of conjunctive queries and arbitrary
denial constraints, which include functional dependencies as a special case. We
report results from experiments evaluating CAvSAT on both synthetic and
real-world databases. These results provide evidence that a SAT-based approach
can give rise to a comprehensive and scalable system for consistent query
answering.Comment: 25 pages including appendix, to appear in the 22nd International
Conference on Theory and Applications of Satisfiability Testin
Conditional Dependencies: A Principled Approach to Improving Data Quality
Abstract. Real-life date is often dirty and costs billions of pounds to businesses worldwide each year. This paper presents a promising ap-proach to improving data quality. It effectively detects and fixes inconsis-tencies in real-life data based on conditional dependencies, an extension of database dependencies by enforcing bindings of semantically related data values. It accurately identifies records from unreliable data sources by leveraging relative candidate keys, an extension of keys for relations by supporting similarity and matching operators across relations. In con-trast to traditional dependencies that were developed for improving the quality of schema, the revised constraints are proposed to improve the quality of data. These constraints yield practical techniques for data re-pairing and record matching in a uniform framework.
A Model of User Preferences for Semantic Services Discovery and Ranking
Current proposals on Semantic Web Services discovery and
ranking are based on user preferences descriptions that often come with
insufficient expressiveness, consequently making more difficult or even
preventing the description of complex user desires. There is a lack of a
general and comprehensive preference model, so discovery and ranking
proposals have to provide ad hoc preference descriptions whose expressiveness
depends on the facilities provided by the corresponding technique,
resulting in user preferences that are tightly coupled with the
underlying formalism being used by each concrete solution. In order to
overcome these problems, in this paper an abstract and sufficiently expressive
model for defining preferences is presented, so that they may be
described in an intuitively and user-friendly manner. The proposed model
is based on a well-known query preference model from database systems,
which provides highly expressive constructors to describe and compose
user preferences semantically. Furthermore, the presented proposal is independent
from the concrete discovery and ranking engines selected, and
may be used to extend current Semantic Web Service frameworks, such
as wsmo, sawsdl, or owl-s. In this paper, the presented model is also
validated against a complex discovery and ranking scenario, and a concrete
implementation of the model in wsmo is outlined.Comisión Interministerial de Ciencia y Tecnología TIN2006-00472Comisión Interministerial de Ciencia y Tecnología TIN2009-07366Junta de Andalucía TIC-253
Data-Oriented Declarative Language for Optimizing Business Processes
There is a signifi cant number of declarative languages to describe business
processes. They tend to be used when business processes need to be fl exible and
adaptable, being not possible to use an imperative description. Declarative languages
in business process have been traditionally used to describe the order of
activities, specifi cally the order allowed or prohibited. Unfortunately, none of them
is worried about a declarative description of exchanged data between the activities
and how they can infl uence the model. In this paper, we analyse the data description
capacity of a variety of declarative languages in business processes. Using this
analysis, we have detected the necessity to include data exchanged aspects in the
declarative descriptions. In order to solve the gap, we propose a Data-Oriented
Optimization Declarative LanguagE, called DOODLE, which includes the process
requirements referred to data description, and the possibility to include an optimization
function about the process output data
Complexity Thresholds in Inclusion Logic
Logics with team semantics provide alternative means for logical
characterization of complexity classes. Both dependence and independence logic
are known to capture non-deterministic polynomial time, and the frontiers of
tractability in these logics are relatively well understood. Inclusion logic is
similar to these team-based logical formalisms with the exception that it
corresponds to deterministic polynomial time in ordered models. In this article
we examine connections between syntactical fragments of inclusion logic and
different complexity classes in terms of two computational problems: maximal
subteam membership and the model checking problem for a fixed inclusion logic
formula. We show that very simple quantifier-free formulae with one or two
inclusion atoms generate instances of these problems that are complete for
(non-deterministic) logarithmic space and polynomial time. Furthermore, we
present a fragment of inclusion logic that captures non-deterministic
logarithmic space in ordered models
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