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A Scheme for Integrating Concrete Domains into Concept Languages
, 1991
"... A drawback which concept languages based on klone have is that all the terminological knowledge has to be defined on an abstract logical level. In many applications, one would like to be able to refer to concrete domains and predicates on these domains when defining concepts. Examples for such conc ..."
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Cited by 262 (19 self)
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A drawback which concept languages based on klone have is that all the terminological knowledge has to be defined on an abstract logical level. In many applications, one would like to be able to refer to concrete domains and predicates on these domains when defining concepts. Examples for such concrete domains are the integers, the real numbers, or also nonarithmetic domains, and predicates could be equality, inequality, or more complex predicates. In the present paper we shall propose a scheme for integrating such concrete domains into concept languages rather than describing a particular extension by some specific concrete domain. We shall define a terminological and an assertional language, and consider the important inference problems such as subsumption, instantiation, and consistency. The formal semantics as well as the reasoning algorithms are given on the scheme level. In contrast to existing klone based systems, these algorithms will be not only sound but also complete. The...
Description Logics in Data Management
, 1995
"... Description logics and reasoners, which are descendants of the klone language, have been studied in depth in Artificial Intelligence. After a brief introduction, we survey in this paper their application to the problems of information management, using the framework of an abstract information serve ..."
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Cited by 177 (12 self)
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Description logics and reasoners, which are descendants of the klone language, have been studied in depth in Artificial Intelligence. After a brief introduction, we survey in this paper their application to the problems of information management, using the framework of an abstract information server equipped with several operations  each involving one or more languages. Specifically, we indicate how one can achieve enhanced access to data and knowledge by using descriptions in languages for schema design and integration, queries, answers, updates, rules, and constraints.
A Semantics and Complete Algorithm for Subsumption in the CLASSIC Description Logic
 Journal of Artificial Intelligence Research
, 1994
"... This paper analyzes the correctness of the subsumption algorithm used in classic, a description logicbased knowledge representation system that is being used in practical applications. In order to deal efficiently with individuals in classic descriptions, the developers have had to use an algori ..."
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Cited by 161 (14 self)
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This paper analyzes the correctness of the subsumption algorithm used in classic, a description logicbased knowledge representation system that is being used in practical applications. In order to deal efficiently with individuals in classic descriptions, the developers have had to use an algorithm that is incomplete with respect to the standard, modeltheoretic semantics for description logics. We provide a variant semantics for descriptions with respect to which the current implementation is complete, and which can be independently motivated. The soundness and completeness of the polynomialtime subsumption algorithm is established using description graphs, which are an abstracted version of the implementation structures used in classic, and are of independent interest. 1. Introduction to Description Logics Data and knowledge bases are models of some part of the natural world. Such models are often built from individual objects that are interrelated by relationships and g...
Learning the CLASSIC Description Logic: Theoretical and Experimental Results
 In Principles of Knowledge Representation and Reasoning: Proceedings of the Fourth International Conference (KR94
, 1994
"... We present a series of theoretical and experimental results on the learnability of description logics. We first extend previous formal learnability results on simple description logics to CClassic, a description logic expressive enough to be practically useful. We then experimentally evaluate two e ..."
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Cited by 92 (7 self)
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We present a series of theoretical and experimental results on the learnability of description logics. We first extend previous formal learnability results on simple description logics to CClassic, a description logic expressive enough to be practically useful. We then experimentally evaluate two extensions of a learning algorithm suggested by the formal analysis. The first extension learns CClassic descriptions from individuals. (The formal results assume that examples are themselves descriptions.) The second extension learns disjunctions of CClassic descriptions from individuals. The experiments, which were conducted using several hundred target concepts from a number of domains, indicate that both extensions reliably learn complex natural concepts. 1 INTRODUCTION One wellknown family of formalisms for representing knowledge are description logics, sometimes also called terminological logics or KLONEtype languages. Description logics have been applied in a number of contexts...
Computing Least Common Subsumers in Description Logics
 PROCEEDINGS OF THE 10TH NATIONAL CONFERENCE ON ARTIFICIAL INTELLIGENCE
, 1992
"... Description logics are a popular formalism for knowledge representation and reasoning. This paper introduces a new operation for description logics: computing the "least common subsumer" of a pair of descriptions. This operation computes the largest set of commonalities between two descrip ..."
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Cited by 90 (14 self)
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Description logics are a popular formalism for knowledge representation and reasoning. This paper introduces a new operation for description logics: computing the "least common subsumer" of a pair of descriptions. This operation computes the largest set of commonalities between two descriptions. After arguing for the usefulness of this operation, we analyze it by relating computation of the least common subsumer to the wellunderstood problem of testing subsumption; a close connection is shown in the restricted case of "structural subsumption". We also present a method for computing the least common subsumer of "attribute chain equalities", and analyze the tractability of computing the least common subsumer of a set of descriptionsan important operation in inductive learning.
Explaining Subsumption in Description Logics
, 1994
"... This paper explores the explanation of subsumption reasoning in Description Logics that are implemented using normalization methods, focusing on the perspective of knowledge engineers. The notion of explanation is specified using a prooftheoretic framework for presenting the inferences supported in ..."
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Cited by 44 (10 self)
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This paper explores the explanation of subsumption reasoning in Description Logics that are implemented using normalization methods, focusing on the perspective of knowledge engineers. The notion of explanation is specified using a prooftheoretic framework for presenting the inferences supported in these systems. The problem of overly long explanations is addressed by decomposing them into smaller, independent steps, using the notions of “atomic description” and “atomic justification”. Implementation aspects are explored by considering the design space and some desiderata for explanation modules. This approach has been implemented for the classic knowledge representation system.
The Learnability of Description Logics with Equality Constraints
 Machine Learning
, 1994
"... Although there is an increasing amount of experimental research on learning concepts expressed in firstorder logic, there are still relatively few formal results on the polynomial learnability of firstorder representations from examples. Most previous analyses in the pacmodel have focused on s ..."
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Cited by 37 (3 self)
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Although there is an increasing amount of experimental research on learning concepts expressed in firstorder logic, there are still relatively few formal results on the polynomial learnability of firstorder representations from examples. Most previous analyses in the pacmodel have focused on subsets of Prolog, and only a few highly restricted subsets have been shown to be learnable. In this paper, we will study instead the learnability of the restricted firstorder logics known as "description logics", also sometimes called "terminological logics" or "KLONEtype languages". Description logics are also subsets of predicate calculus, but are expressed using a different syntax, allowing a different set of syntactic restrictions to be explored. We first define a simple description logic, summarize some results on its expressive power, and then analyze its learnability. It is shown that the full logic cannot be tractably learned. However, syntactic restrictions exist that enable tractable learning from positive examples alone, independent of the size of the vocabulary used to describe examples. The learnable sublanguage appears to be incomparable in expressive power to any subset of firstorder logic previously known to be learnable.
CLASSIC Learning
 In Proceedings of the Seventh Annual ACM Conference on Computational Learning Theory
, 1991
"... . Description logics, also called terminological logics, are commonly used in knowledgebased systems to describe objects and their relationships. We investigate the learnability of a typical description logic, Classic, and show that Classic sentences are learnable in polynomial time in the exact lea ..."
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Cited by 31 (1 self)
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. Description logics, also called terminological logics, are commonly used in knowledgebased systems to describe objects and their relationships. We investigate the learnability of a typical description logic, Classic, and show that Classic sentences are learnable in polynomial time in the exact learning model using equivalence queries and membership queries (which are in essence, "subsumption queries"we show a prediction hardness result for the more traditional membership queries that convey information about specific individuals). We show that membership queries alone are insufficient for polynomial time learning of Classic sentences. Combined with earlier negative results (Cohen & Hirsh, 1994a) showing that, given standard complexity theoretic assumptions, equivalence queries alone are insufficient (or random examples alone in the PAC setting are insufficient), this shows that both sources of information are necessary for efficient learning in that neither type alone is sufficie...
Learnability of Description Logics
 IN PROCEEDINGS OF THE FOURTH ANNUAL WORKSHOP ON COMPUTATIONAL LEARNING THEORY
, 1992
"... This paper considers the learnability of subsets of firstorder logic. Prior work has established two boundaries of learnability: Haussler [ 1989 ] has shown that conjunctions in firstorder logic cannot be learned in the Valiant model, even if the form of the conjunction is highly restricted; ..."
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Cited by 9 (5 self)
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This paper considers the learnability of subsets of firstorder logic. Prior work has established two boundaries of learnability: Haussler [ 1989 ] has shown that conjunctions in firstorder logic cannot be learned in the Valiant model, even if the form of the conjunction is highly restricted; on the other hand, Valiant [ 1984 ] has shown that propositional conjunctions are learnable. In this