210 research outputs found
Query Rewriting and Optimization for Ontological Databases
Ontological queries are evaluated against a knowledge base consisting of an
extensional database and an ontology (i.e., a set of logical assertions and
constraints which derive new intensional knowledge from the extensional
database), rather than directly on the extensional database. The evaluation and
optimization of such queries is an intriguing new problem for database
research. In this paper, we discuss two important aspects of this problem:
query rewriting and query optimization. Query rewriting consists of the
compilation of an ontological query into an equivalent first-order query
against the underlying extensional database. We present a novel query rewriting
algorithm for rather general types of ontological constraints which is
well-suited for practical implementations. In particular, we show how a
conjunctive query against a knowledge base, expressed using linear and sticky
existential rules, that is, members of the recently introduced Datalog+/-
family of ontology languages, can be compiled into a union of conjunctive
queries (UCQ) against the underlying database. Ontological query optimization,
in this context, attempts to improve this rewriting process so to produce
possibly small and cost-effective UCQ rewritings for an input query.Comment: arXiv admin note: text overlap with arXiv:1312.5914 by other author
Heuristic Ranking in Tightly Coupled Probabilistic Description Logics
The Semantic Web effort has steadily been gaining traction in the recent
years. In particular,Web search companies are recently realizing that their
products need to evolve towards having richer semantic search capabilities.
Description logics (DLs) have been adopted as the formal underpinnings for
Semantic Web languages used in describing ontologies. Reasoning under
uncertainty has recently taken a leading role in this arena, given the nature
of data found on theWeb. In this paper, we present a probabilistic extension of
the DL EL++ (which underlies the OWL2 EL profile) using Markov logic networks
(MLNs) as probabilistic semantics. This extension is tightly coupled, meaning
that probabilistic annotations in formulas can refer to objects in the
ontology. We show that, even though the tightly coupled nature of our language
means that many basic operations are data-intractable, we can leverage a
sublanguage of MLNs that allows to rank the atomic consequences of an ontology
relative to their probability values (called ranking queries) even when these
values are not fully computed. We present an anytime algorithm to answer
ranking queries, and provide an upper bound on the error that it incurs, as
well as a criterion to decide when results are guaranteed to be correct.Comment: Appears in Proceedings of the Twenty-Eighth Conference on Uncertainty
in Artificial Intelligence (UAI2012
X-som: A flexible ontology mapper
System interoperability is a well known issue, especially for heterogeneous information systems, where ontologybased representations may support automatic and usertransparent integration. In this paper we present X-SOM: an ontology mapping and integration tool. The contribution of our tool is a modular and extensible architecture that automatically combines several matching techniques by means of a neural network, performing also ontology debugging to avoid inconsistencies. Besides describing the tool components, we discuss the prototype implementation, which has been tested against the OAEI 2006 benchmark with promising results.
Semantic pervasive advertising
Abstract. Pervasive advertising targets consumers on-the-move with ads displayed on their mobile devices. As for web advertising, ads are distributed by embedding them into websites and apps, easily flooding consumers with a large number of uninteresting offers. As the pervasive setting amplifies traditional issues such as targeting, cost, and privacy, we argue the need for a new perspective on the problem. We introduce PervADs, a privacy-preserving, user-centric, and pervasive ads-distribution platform which uses semantic technologies to reason about the consumer's context and the intended target of the ads
Peritonitis: laparoscopic approach
BACKGROUND: Laparoscopy has became as the preferred surgical approach to a number of different diseases because it allows a correct diagnosis and treatment at the same time. In abdominal emergencies, both components of treatment – exploration to identify the causative pathology and performance of an appropriate operation – can often be accomplished via laparoscopy. There is still a debate of peritonitis as a contraindication to this kind of approach. Aim of the present work is to illustrate retrospectively the results of a case-control experience of laparoscopic vs. open surgery for abdominal peritonitis emergencies carried out at our institution. METHODS: From January 1992 and January 2002 a total of 935 patients (mean age 42.3 ± 17.2 years) underwent emergent and/or urgent surgery. Among them, 602 (64.3%) were operated on laparoscopically (of whom 112 -18.7% – with peritonitis), according to the presence of a surgical team trained in laparoscopy. Patients with a history of malignancy, more than two previous major abdominal surgeries or massive bowel distension were not treated Laparoscopically. Peritonitis was not considered contraindication to Laparoscopy. RESULTS: The conversion rate was 23.2% in patients with peritonitis and was mainly due to the presence of dense intra-abdominal adhesions. Major complications ranged as high as 5.3% with a postoperative mortality of 1.7%. A definitive diagnosis was accomplished in 85.7% (96 pat.) of cases, and 90.6% (87) of these patients were treated successfully by Laparoscopy. CONCLUSION: Even if limited by its retrospective feature, the present experience let us to consider the Laparoscopic approach to abdominal peritonitis emergencies a safe and effective as conventional surgery, with a higher diagnostic yield and allows for lesser trauma and a more rapid postoperative recovery. Such features make Laparoscopy a challenging alternative to open surgery in the management algorithm for abdominal peritonitis emergencies
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