The deployment of Description Logics (DLs) and Answer Set Programming (ASP), which are well-known... more The deployment of Description Logics (DLs) and Answer Set Programming (ASP), which are well-known knowledge representation and reasoning formalisms, to a growing range of applications has created the need for novel reasoning algorithms and methods. Recently, knots have been introduced as a tool to facilitate reasoning tasks in extensions of ASP with functions symbols. They were then also fruitfully applied for query answering in Description Logics, hinging on the forest-shaped model property of knowledge bases.
Abstract In this paper, we present the computational model of an agent for CSCL environments, bas... more Abstract In this paper, we present the computational model of an agent for CSCL environments, based on the answer set programming (ASP) formalism. The complete model is formally presented in the declarative language of DLV, a system for implementing ASP models.
Abstract The safe belief semantics uses intermediate logics to define an extension of answer sets... more Abstract The safe belief semantics uses intermediate logics to define an extension of answer sets to all propositional formulas, but only considering one kind of negation. In this work we extend safe beliefs adding the strong negation connective. The main feature of our extension is that strong negation can occur before any formula, and not only at the atomic level.
Abstract. This paper presents the pertinence of the use of the Answer Set Programming (ASP) forma... more Abstract. This paper presents the pertinence of the use of the Answer Set Programming (ASP) formalism for developing a computational model of a software agent for Computer Supported Collaborative Learning (CSCL) environments.
Abstract In this paper we present a logic formalization of amodel which allows us to represent, c... more Abstract In this paper we present a logic formalization of amodel which allows us to represent, create and maintaina Learner Model for CSCL environments in a clear andadequate manner, in order to use it as the set of beliefs anagent holds about its user, supporting the effectivecollaboration between the learners in the community. Ourmodel includes a representation method for theknowledge domain and the agent's beliefs about thelearner, as well as an inference system.
Abstract. Answering conjunctive queries over knowledge bases in Description Logics (DLs) has rece... more Abstract. Answering conjunctive queries over knowledge bases in Description Logics (DLs) has received increasing attention in the last years. In the present paper, we study the computational complexity of deciding conjunctive query entailment in expressive DLs that support transitive roles and role hierarchies, but no inverse roles. We show that the problem is 2-EXPTIME-hard for the DL SH; combining this with the known matching upper bound, we thus precisely characterize the complexity of the problem for SH.
Abstract Answering conjunctive queries (CQs) has been recognized as a key task for the usage of D... more Abstract Answering conjunctive queries (CQs) has been recognized as a key task for the usage of Description Logics (DLs) in a number of applications, and has thus been studied by many authors. In this paper, we present an algorithm for this problem in the DL ALCH which works in exponential time. It improves over previous algorithms which require double exponential time and is worst-case optimal, as already satisfiability testing in ALC is EXPTIME-complete.
Answering conjunctive queries (CQs) has been recognized as an important task for the widening use... more Answering conjunctive queries (CQs) has been recognized as an important task for the widening use of Description Logics (DLs) in a number of applications. The problem has been studied by many authors, who developed a number of different techniques for its solution. We present a novel approach to CQ answering that is based on knots, which are schematic trees of depth at most one that can be used to represent the terminological information represented in a TBox.
Abstract Description Logics (DLs) are the formal foundations of the standard web ontology languag... more Abstract Description Logics (DLs) are the formal foundations of the standard web ontology languages OWL-DL and OWL-Lite. In the Semantic Web and other domains, ontologies are increasingly seen also as a mechanism to access and query data repositories.
Abstract Horn fragments of Description Logics (DLs) have gained popularity because they provide a... more Abstract Horn fragments of Description Logics (DLs) have gained popularity because they provide a beneficial trade-off between expressive power and computational complexity and, more specifically, are usually tractable wrt data complexity. Despite their potential, and partly due to the intricate interaction of nominals (O), inverses (I) and counting (Q), such fragments had not been studied so far for the DLs SHOIQ and SROIQ that underly OWL1and2.
Abstract In this work we describe the theoretical foundations and the implementation of a new aut... more Abstract In this work we describe the theoretical foundations and the implementation of a new automata-based technique for reasoning over expressive Description Logics that is worst-case optimal and lends itself to an efficient implementation. In order to show the feasibility of the approach, we have realized a working prototype of a reasoner based upon these techniques. An experimental evaluation of this prototype shows encouraging results.
Abstract Expressive Description Logics (DLs) have been advocated as formalisms for modeling the d... more Abstract Expressive Description Logics (DLs) have been advocated as formalisms for modeling the domain of interest in various application areas. An important requirement is the ability to answer complex queries beyond instance retrieval, taking into account constraints expressed in a knowledge base.
Abstract. Answering conjunctive queries (CQs) has been recognized as a key task for the usage of ... more Abstract. Answering conjunctive queries (CQs) has been recognized as a key task for the usage of Description Logics (DLs) in a number of applications. The problem has been studied by many authors, who developed a number of different techniques for it. We present a novel method for CQ answering based on knots, which are schematic trees of depth≤ 1. It yields an algorithm for CQ answering that works in exponential time for ALCH and for large classes of CQs in SH.
The deployment of Description Logics (DLs) and Answer Set Programming (ASP), which are well-known... more The deployment of Description Logics (DLs) and Answer Set Programming (ASP), which are well-known knowledge representation and reasoning formalisms, to a growing range of applications has created the need for novel reasoning algorithms and methods. Recently, knots have been introduced as a tool to facilitate reasoning tasks in extensions of ASP with functions symbols. They were then also fruitfully applied for query answering in Description Logics, hinging on the forest-shaped model property of knowledge bases.
Abstract In this paper, we present the computational model of an agent for CSCL environments, bas... more Abstract In this paper, we present the computational model of an agent for CSCL environments, based on the answer set programming (ASP) formalism. The complete model is formally presented in the declarative language of DLV, a system for implementing ASP models.
Abstract The safe belief semantics uses intermediate logics to define an extension of answer sets... more Abstract The safe belief semantics uses intermediate logics to define an extension of answer sets to all propositional formulas, but only considering one kind of negation. In this work we extend safe beliefs adding the strong negation connective. The main feature of our extension is that strong negation can occur before any formula, and not only at the atomic level.
Abstract. This paper presents the pertinence of the use of the Answer Set Programming (ASP) forma... more Abstract. This paper presents the pertinence of the use of the Answer Set Programming (ASP) formalism for developing a computational model of a software agent for Computer Supported Collaborative Learning (CSCL) environments.
Abstract In this paper we present a logic formalization of amodel which allows us to represent, c... more Abstract In this paper we present a logic formalization of amodel which allows us to represent, create and maintaina Learner Model for CSCL environments in a clear andadequate manner, in order to use it as the set of beliefs anagent holds about its user, supporting the effectivecollaboration between the learners in the community. Ourmodel includes a representation method for theknowledge domain and the agent's beliefs about thelearner, as well as an inference system.
Abstract. Answering conjunctive queries over knowledge bases in Description Logics (DLs) has rece... more Abstract. Answering conjunctive queries over knowledge bases in Description Logics (DLs) has received increasing attention in the last years. In the present paper, we study the computational complexity of deciding conjunctive query entailment in expressive DLs that support transitive roles and role hierarchies, but no inverse roles. We show that the problem is 2-EXPTIME-hard for the DL SH; combining this with the known matching upper bound, we thus precisely characterize the complexity of the problem for SH.
Abstract Answering conjunctive queries (CQs) has been recognized as a key task for the usage of D... more Abstract Answering conjunctive queries (CQs) has been recognized as a key task for the usage of Description Logics (DLs) in a number of applications, and has thus been studied by many authors. In this paper, we present an algorithm for this problem in the DL ALCH which works in exponential time. It improves over previous algorithms which require double exponential time and is worst-case optimal, as already satisfiability testing in ALC is EXPTIME-complete.
Answering conjunctive queries (CQs) has been recognized as an important task for the widening use... more Answering conjunctive queries (CQs) has been recognized as an important task for the widening use of Description Logics (DLs) in a number of applications. The problem has been studied by many authors, who developed a number of different techniques for its solution. We present a novel approach to CQ answering that is based on knots, which are schematic trees of depth at most one that can be used to represent the terminological information represented in a TBox.
Abstract Description Logics (DLs) are the formal foundations of the standard web ontology languag... more Abstract Description Logics (DLs) are the formal foundations of the standard web ontology languages OWL-DL and OWL-Lite. In the Semantic Web and other domains, ontologies are increasingly seen also as a mechanism to access and query data repositories.
Abstract Horn fragments of Description Logics (DLs) have gained popularity because they provide a... more Abstract Horn fragments of Description Logics (DLs) have gained popularity because they provide a beneficial trade-off between expressive power and computational complexity and, more specifically, are usually tractable wrt data complexity. Despite their potential, and partly due to the intricate interaction of nominals (O), inverses (I) and counting (Q), such fragments had not been studied so far for the DLs SHOIQ and SROIQ that underly OWL1and2.
Abstract In this work we describe the theoretical foundations and the implementation of a new aut... more Abstract In this work we describe the theoretical foundations and the implementation of a new automata-based technique for reasoning over expressive Description Logics that is worst-case optimal and lends itself to an efficient implementation. In order to show the feasibility of the approach, we have realized a working prototype of a reasoner based upon these techniques. An experimental evaluation of this prototype shows encouraging results.
Abstract Expressive Description Logics (DLs) have been advocated as formalisms for modeling the d... more Abstract Expressive Description Logics (DLs) have been advocated as formalisms for modeling the domain of interest in various application areas. An important requirement is the ability to answer complex queries beyond instance retrieval, taking into account constraints expressed in a knowledge base.
Abstract. Answering conjunctive queries (CQs) has been recognized as a key task for the usage of ... more Abstract. Answering conjunctive queries (CQs) has been recognized as a key task for the usage of Description Logics (DLs) in a number of applications. The problem has been studied by many authors, who developed a number of different techniques for it. We present a novel method for CQ answering based on knots, which are schematic trees of depth≤ 1. It yields an algorithm for CQ answering that works in exponential time for ALCH and for large classes of CQs in SH.
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Papers by Magdalena Ortiz