84,464 research outputs found
An introduction to description logics and query rewriting
This chapter gives an overview of the description logics underlying the OWL 2 Web Ontology Language and its three tractable profiles, OWL 2 RL, OWL 2 EL and OWL 2 QL. We consider the syntax and semantics of these description logics as well as main reasoning tasks and their computational complexity. We also discuss the semantical foundations for fist-order and datalog rewritings of conjunctive queries over knowledge bases given in the OWL2 profiles, and outline the architecture of the ontology-based data access system Ontop
Introduction to the TPLP special issue, logic programming in databases: From Datalog to semantic-web rules
Much has happened in data and knowledge base research since the introduction
of the relational model in Codd (1970) and its strong logical foundations influence
its advances ever since. Logic has been a common ground where Database and
Artificial Intelligence research competed and collaborated with each other for a
long time (Abiteboul et al. 1995). The product of this joint effort has been a set of
logic-based formalisms, such as the Relational Calculus (Codd 1970), Datalog (Ceri
et al. 1990), Description Logics (Baader et al. 2007), etc., capturing not only the
structure but also the semantics of data in an explicit way, thus enabling complex
inference procedures.This special issue contains three rigorously reviewed articles addressing problems
that span from Query Answering to Data Mining. All these contributions have their
roots in the foundational formalisms of Data and Knowledge Bases such as Logic
Programming, Description Logic and Hybrid Logics, representing a clear example
of the effort that the Database and the Semantic-Web communities are producing to
bridge the various schools of thinking in modern Data and Knowledge Management
Some reflections on knowledge representation in the semantic web
The knowledge representation technology Description Logics (DLs) has become an important component of developments around the Semantic Web. It is suggested here that in order to be really useful, the knowledge represented in DLs should in some fundamental way reflect the way the human mind organises and structures the same knowledge. There is a short historical review of some relevant background work in cognitive psychology, including WordNet. This is followed by a brief introduction to the importance of automatic classification in DLs before considering some issues around ontologies
Basic Description Logics
This chapter provides an introduction to Description Logics as a formal language for representing knowledge and reasoning about it. It first gives a short overview of the ideas underlying Description Logics. Then it introduces syntax and semantics, covering the basic constructors that are used in systems or have been introduced in the literature, and the way these constructors can be used to build knowledge bases. Finally, it defines the typical inference problems, shows how they are interrelated, and describes different approaches for effectively solving these problems. Some of the topics that are only briefly mentioned in this chapter will be treated in more detail in subsequent chapters
Named Models in Coalgebraic Hybrid Logic
Hybrid logic extends modal logic with support for reasoning about individual
states, designated by so-called nominals. We study hybrid logic in the broad
context of coalgebraic semantics, where Kripke frames are replaced with
coalgebras for a given functor, thus covering a wide range of reasoning
principles including, e.g., probabilistic, graded, default, or coalitional
operators. Specifically, we establish generic criteria for a given coalgebraic
hybrid logic to admit named canonical models, with ensuing completeness proofs
for pure extensions on the one hand, and for an extended hybrid language with
local binding on the other. We instantiate our framework with a number of
examples. Notably, we prove completeness of graded hybrid logic with local
binding
Hypertableau Reasoning for Description Logics
We present a novel reasoning calculus for the description logic SHOIQ^+---a
knowledge representation formalism with applications in areas such as the
Semantic Web. Unnecessary nondeterminism and the construction of large models
are two primary sources of inefficiency in the tableau-based reasoning calculi
used in state-of-the-art reasoners. In order to reduce nondeterminism, we base
our calculus on hypertableau and hyperresolution calculi, which we extend with
a blocking condition to ensure termination. In order to reduce the size of the
constructed models, we introduce anywhere pairwise blocking. We also present an
improved nominal introduction rule that ensures termination in the presence of
nominals, inverse roles, and number restrictions---a combination of DL
constructs that has proven notoriously difficult to handle. Our implementation
shows significant performance improvements over state-of-the-art reasoners on
several well-known ontologies
A strengthening of rational closure in DLs: reasoning about multiple aspects
We propose a logical analysis of the concept of typicality, central in human
cognition (Rosch,1978). We start from a previously proposed extension of the
basic Description Logic ALC (a computationally tractable fragment of First
Order Logic, used to represent concept inclusions and ontologies) with a
typicality operator T that allows to consistently represent the attribution to
classes of individuals of properties with exceptions (as in the classic example
(i) typical birds fly, (ii) penguins are birds but (iii) typical penguins don't
fly). We then strengthen this extension in order to separately reason about the
typicality with respect to different aspects (e.g., flying, having nice
feather: in the previous example, penguins may not inherit the property of
flying, for which they are exceptional, but can nonetheless inherit other
properties, such as having nice feather)
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