4,617 research outputs found
Ontology-Based Data Access and Integration
An ontology-based data integration (OBDI) system is an information management system consisting of three components: an ontology, a set of data sources, and the mapping between the two. The ontology is a conceptual, formal description of the domain of interest to a given organization (or a community of users), expressed in terms of relevant concepts, attributes of concepts, relationships between concepts, and logical assertions characterizing the domain knowledge. The data sources are the repositories accessible by the organization where data concerning the domain are stored. In the general case, such repositories are numerous, heterogeneous, each one managed and maintained independently from the others. The mapping is a precise specification of the correspondence between the data contained in the data sources and the elements of the ontology. The main purpose of an OBDI system is to allow information consumers to query the data using the elements in the ontology as predicates.
In the special case where the organization manages a single data source, the term ontology-based data access (ODBA) system is used
Temporal Data Modeling and Reasoning for Information Systems
Temporal knowledge representation and reasoning is a major research field in Artificial
Intelligence, in Database Systems, and in Web and Semantic Web research. The ability to
model and process time and calendar data is essential for many applications like appointment
scheduling, planning, Web services, temporal and active database systems, adaptive
Web applications, and mobile computing applications. This article aims at three complementary
goals. First, to provide with a general background in temporal data modeling
and reasoning approaches. Second, to serve as an orientation guide for further specific
reading. Third, to point to new application fields and research perspectives on temporal
knowledge representation and reasoning in the Web and Semantic Web
A Goal-Directed Implementation of Query Answering for Hybrid MKNF Knowledge Bases
Ontologies and rules are usually loosely coupled in knowledge representation
formalisms. In fact, ontologies use open-world reasoning while the leading
semantics for rules use non-monotonic, closed-world reasoning. One exception is
the tightly-coupled framework of Minimal Knowledge and Negation as Failure
(MKNF), which allows statements about individuals to be jointly derived via
entailment from an ontology and inferences from rules. Nonetheless, the
practical usefulness of MKNF has not always been clear, although recent work
has formalized a general resolution-based method for querying MKNF when rules
are taken to have the well-founded semantics, and the ontology is modeled by a
general oracle. That work leaves open what algorithms should be used to relate
the entailments of the ontology and the inferences of rules. In this paper we
provide such algorithms, and describe the implementation of a query-driven
system, CDF-Rules, for hybrid knowledge bases combining both (non-monotonic)
rules under the well-founded semantics and a (monotonic) ontology, represented
by a CDF Type-1 (ALQ) theory. To appear in Theory and Practice of Logic
Programming (TPLP
Knowledge Transformations between Frame Systems and RDB Systems
For decades, researchers in knowledge representation (KR) have argued for and against various choices in KR formalisms, such as Rules, Frames, Semantic nets, and Formal logic. In this paper, we present a set of transformations that can be used to move knowledge across two fundamentally different KR formalisms: Frame-based systems and Relational database systems (RDBs). We also describe partial implementations of these transformations for a specific pair of such systems: ProtƩgƩ and the Postgres RDB system
The coupled-cluster approach to quantum many-body problem in a three-Hilbert-space reinterpretation
The quantum many-body bound-state problem in its computationally successful
coupled cluster method (CCM) representation is reconsidered. In conventional
practice one factorizes the ground-state wave functions which live in the "physical" Hilbert space using
an elementary ansatz for plus a formal expansion of in an
operator basis of multi-configurational creation operators. In our paper a
reinterpretation of the method is proposed. Using parallels between the CCM and
the so called quasi-Hermitian, alias three-Hilbert-space (THS), quantum
mechanics, the CCM transition from the known microscopic Hamiltonian (denoted
by usual symbol ), which is self-adjoint in , to its
effective lower-case isospectral avatar , is assigned a
THS interpretation. In the opposite direction, a THS-prescribed, non-CCM,
innovative reinstallation of Hermiticity is shown to be possible for the CCM
effective Hamiltonian , which only appears manifestly non-Hermitian in
its own ("friendly") Hilbert space . This goal is achieved via
an ad hoc amendment of the inner product in , thereby yielding
the third ("standard") Hilbert space . Due to the resulting
exact unitary equivalence between the first and third spaces, , the indistinguishability of predictions
calculated in these alternative physical frameworks is guaranteed.Comment: 15 page
Polynomial-Time Reasoning Support for Design and Maintenance of Large-Scale Biomedical Ontologies
Description Logics (DLs) belong to a successful family of knowledge representation formalisms with two key assets: formally well-defined semantics which allows to represent knowledge in an unambiguous way and automated reasoning which allows to infer implicit knowledge from the one given explicitly. This thesis investigates various reasoning techniques for tractable DLs in the EL family which have been implemented in the CEL system. It suggests that the use of the lightweight DLs, in which reasoning is tractable, is beneficial for ontology design and maintenance both in terms of expressivity and scalability. The claim is supported by a case study on the renown medical ontology SNOMED CT and extensive empirical evaluation on several large-scale biomedical ontologies
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