187 research outputs found
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
The tractability frontier of well-designed SPARQL queries
We study the complexity of query evaluation of SPARQL queries. We focus on
the fundamental fragment of well-designed SPARQL restricted to the AND,
OPTIONAL and UNION operators. Our main result is a structural characterisation
of the classes of well-designed queries that can be evaluated in polynomial
time. In particular, we introduce a new notion of width called domination
width, which relies on the well-known notion of treewidth. We show that, under
some complexity theoretic assumptions, the classes of well-designed queries
that can be evaluated in polynomial time are precisely those of bounded
domination width
Relating Structure and Power: Comonadic Semantics for Computational Resources
Combinatorial games are widely used in finite model theory, constraint
satisfaction, modal logic and concurrency theory to characterize logical
equivalences between structures. In particular, Ehrenfeucht-Fraisse games,
pebble games, and bisimulation games play a central role. We show how each of
these types of games can be described in terms of an indexed family of comonads
on the category of relational structures and homomorphisms. The index k is a
resource parameter which bounds the degree of access to the underlying
structure. The coKleisli categories for these comonads can be used to give
syntax-free characterizations of a wide range of important logical
equivalences. Moreover, the coalgebras for these indexed comonads can be used
to characterize key combinatorial parameters: tree-depth for the
Ehrenfeucht-Fraisse comonad, tree-width for the pebbling comonad, and
synchronization-tree depth for the modal unfolding comonad. These results pave
the way for systematic connections between two major branches of the field of
logic in computer science which hitherto have been almost disjoint: categorical
semantics, and finite and algorithmic model theory.Comment: To appear in Proceedings of Computer Science Logic 201
The k-variable property is stronger than H-dimension k
Accepted versio
Composition with Target Constraints
It is known that the composition of schema mappings, each specified by
source-to-target tgds (st-tgds), can be specified by a second-order tgd (SO
tgd). We consider the question of what happens when target constraints are
allowed. Specifically, we consider the question of specifying the composition
of standard schema mappings (those specified by st-tgds, target egds, and a
weakly acyclic set of target tgds). We show that SO tgds, even with the
assistance of arbitrary source constraints and target constraints, cannot
specify in general the composition of two standard schema mappings. Therefore,
we introduce source-to-target second-order dependencies (st-SO dependencies),
which are similar to SO tgds, but allow equations in the conclusion. We show
that st-SO dependencies (along with target egds and target tgds) are sufficient
to express the composition of every finite sequence of standard schema
mappings, and further, every st-SO dependency specifies such a composition. In
addition to this expressive power, we show that st-SO dependencies enjoy other
desirable properties. In particular, they have a polynomial-time chase that
generates a universal solution. This universal solution can be used to find the
certain answers to unions of conjunctive queries in polynomial time. It is easy
to show that the composition of an arbitrary number of standard schema mappings
is equivalent to the composition of only two standard schema mappings. We show
that surprisingly, the analogous result holds also for schema mappings
specified by just st-tgds (no target constraints). This is proven by showing
that every SO tgd is equivalent to an unnested SO tgd (one where there is no
nesting of function symbols). Similarly, we prove unnesting results for st-SO
dependencies, with the same types of consequences.Comment: This paper is an extended version of: M. Arenas, R. Fagin, and A.
Nash. Composition with Target Constraints. In 13th International Conference
on Database Theory (ICDT), pages 129-142, 201
Dependence Logic with Generalized Quantifiers: Axiomatizations
We prove two completeness results, one for the extension of dependence logic
by a monotone generalized quantifier Q with weak interpretation, weak in the
meaning that the interpretation of Q varies with the structures. The second
result considers the extension of dependence logic where Q is interpreted as
"there exists uncountable many." Both of the axiomatizations are shown to be
sound and complete for FO(Q) consequences.Comment: 17 page
Psychosocial and cognitive function in children with nephrotic syndrome: association with disease and treatment variables
BackgroundTo investigate possible differences in emotional/behavioral problems and cognitive function in children with nephrotic syndrome compared to healthy controls and to examine the effect of disease-specific and steroid treatment-specific characteristics on the abovementioned variables.
MethodsForty-one patients with nephrotic syndrome (23 boys, age range: 4.4-15.2 years) and 42 sex- and age-matched healthy control subjects (20 boys, age range: 4.1-13.4 years) were enrolled in the study. Disease (severity, age of diagnosis, duration) and steroid treatment (total duration, present methylprednisolone dose and duration of present dose) data were collected. In order to assess children’s emotional/behavioral problems, the Child Behavior Checklist was administered. The Wechsler Intelligence Scale for Children – Third Edition was administered to assess Full-Scale, Verbal, and Performance intelligence quotient (IQ) scores.
ResultsThe patients presented with more internalizing problems (P = 0.015), including withdrawal (P = 0.012) and somatic complaints (P = 0 .011), but not more anxiety/depression or externalizing problems. A significant association was found between severity of disease and somatic complaints (P = 0.017) as well as externalizing problems (P = 0.030). Years of illness were significantly more in those presenting with abnormal anxiety/depression (P = 0.011). Duration of steroid medication was significantly higher among those presenting with abnormal anxiety/depression (P = 0.011) and externalizing problems (P = 0.039). IQ was not associated significantly with disease or steroid treatment variables.
ConclusionsPsychosocial factors and outcomes may be important correlates of children’s nephrotic syndrome and potential targets of thorough assessment and treatment
Psychometric properties of the Farsi translation of the kiddie schedule for affective disorders and schizophrenia-present and lifetime version
BACKGROUND: Semi-structural clinical interviews are very important in the area of mental health research and services. There were no studies of the reliability and validity of the Farsi (Persian) version of Kiddie Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version (K-SADS-PL) in Iran. This study compares the results of face-to-face, semi-structural interview and clinical interview by a child and adolescent psychiatrist. METHOD: Subjects were 109 children and adolescents recruited to the child and adolescent psychiatry outpatient clinic of Hafez Hospital. Order of interview (in-psychiatrist or the semi-structural interview) was determined using random assignment within a counterbalanced framework. After, translation and back translation of K-SADS-PL, the Farsi version of K-SADS-PL was provided and used in the study. The interviewer was unaware of the child and adolescent psychiatrist diagnosis at the time of making the interview. Consensual validity, test-retest and inter-rater reliability, sensitivity, specifity, positive and negative predictive validity for the disorders were studied. RESULTS: Consensual validity of all of the psychiatric disorders was good to excellent. It was highest for panic disorder, conduct disorder, and simple phobia. Consensual validity of anorexia nervosa was 0.49. There was sufficient validity and test-retest and inter-rater reliability and good to excellent sensitivity and specifity and positive and negative predictive validity for nearly all of the disorders. Test-retest reliabilities of attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and tic disorder were 0.81, 0.67, and 0.56; respectively. Inter-rater reliabilities of ADHD, and ODD were 0.69 and 0.69. Tic disorder, post traumatic disorder, panic disorder, and ADHD had the highest positive predictive validities. CONCLUSION: The Farsi version of K-SADS-PL is a valid and reliable interview instrument for use in assessing and diagnosising child and adolescent psychiatric disorders
Answering Non-Monotonic Queries in Relational Data Exchange
Relational data exchange is the problem of translating relational data from a
source schema into a target schema, according to a specification of the
relationship between the source data and the target data. One of the basic
issues is how to answer queries that are posed against target data. While
consensus has been reached on the definitive semantics for monotonic queries,
this issue turned out to be considerably more difficult for non-monotonic
queries. Several semantics for non-monotonic queries have been proposed in the
past few years. This article proposes a new semantics for non-monotonic
queries, called the GCWA*-semantics. It is inspired by semantics from the area
of deductive databases. We show that the GCWA*-semantics coincides with the
standard open world semantics on monotonic queries, and we further explore the
(data) complexity of evaluating non-monotonic queries under the
GCWA*-semantics. In particular, we introduce a class of schema mappings for
which universal queries can be evaluated under the GCWA*-semantics in
polynomial time (data complexity) on the core of the universal solutions.Comment: 55 pages, 3 figure
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