�ݺ�ߣshows by User: magkades

�ݺ�ߣshows by User: magkades / http://www.slideshare.net/images/logo.gif �ݺ�ߣshows by User: magkades / Wed, 01 Apr 2015 13:38:19 GMT �ݺ�ߣShare feed for �ݺ�ߣshows by User: magkades thesis-despoina /slideshow/thesisdespoina/46550462 9fe07876-fdb6-4458-b9db-a5c0138efd0c-150401133819-conversion-gate01
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thesis-despoina from Despoina Magka

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0 Computing Stable Models for Nonmonotonic Existential Rules /slideshow/jcai-13slides/27057698 jcai-13-slides-131010065936-phpapp01
We consider function-free existential rules extended with nonmonotonic negation under a stable model semantics. We present new acyclicity and stratiﬁcation conditions that identify a large class of rule sets having ﬁnite, unique stable models, and we show how the addition of constraints on the input facts can further extend this class. Checking these conditions is computationally feasible, and we provide tight complexity bounds. Finally, we demonstrate how these new methods allowed us to solve relevant reasoning problems over a real-world knowledge base from biochemistry using an off-the-shelf answer set programming engine.]]>
We consider function-free existential rules extended with nonmonotonic negation under a stable model semantics. We present new acyclicity and stratiﬁcation conditions that identify a large class of rule sets having ﬁnite, unique stable models, and we show how the addition of constraints on the input facts can further extend this class. Checking these conditions is computationally feasible, and we provide tight complexity bounds. Finally, we demonstrate how these new methods allowed us to solve relevant reasoning problems over a real-world knowledge base from biochemistry using an off-the-shelf answer set programming engine.]]> Thu, 10 Oct 2013 06:59:36 GMT /slideshow/jcai-13slides/27057698 magkades@slideshare.net(magkades) Computing Stable Models for Nonmonotonic Existential Rules magkades We consider function-free existential rules extended with nonmonotonic negation under a stable model semantics. We present new acyclicity and stratiﬁcation conditions that identify a large class of rule sets having ﬁnite, unique stable models, and we show how the addition of constraints on the input facts can further extend this class. Checking these conditions is computationally feasible, and we provide tight complexity bounds. Finally, we demonstrate how these new methods allowed us to solve relevant reasoning problems over a real-world knowledge base from biochemistry using an off-the-shelf answer set programming engine.�� <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/jcai-13-slides-131010065936-phpapp01-thumbnail.jpg?width=120&height=120&fit=bounds" /> We consider function-free existential rules extended with nonmonotonic negation under a stable model semantics. We present new acyclicity and stratiﬁcation conditions that identify a large class of rule sets having ﬁnite, unique stable models, and we show how the addition of constraints on the input facts can further extend this class. Checking these conditions is computationally feasible, and we provide tight complexity bounds. Finally, we demonstrate how these new methods allowed us to solve relevant reasoning problems over a real-world knowledge base from biochemistry using an off-the-shelf answer set programming engine.��

Computing Stable Models for Nonmonotonic Existential Rules from Despoina Magka

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0 Ontology-Based Classification of Molecules: a Logic Programming Approach /slideshow/ontologybased-classification-of-molecules-a-logic-programming-approach/15450084 swat4lsslides-magka-121202063149-phpapp02
We describe a prototype that performs structure-based classification of molecular structures. The software we present implements a sound and com- plete reasoning procedure of a formalism that extends logic programming and builds upon the DLV deductive databases system. We capture a wide range of chemical classes that are not expressible with OWL-based formalisms such as cyclic molecules, saturated molecules and alkanes. In terms of performance, a no- ticeable improvement is observed in comparison with previous approaches. Our evaluation has discovered subsumptions that are missing from the the manually curated ChEBI ontology as well as discrepancies with respect to existing subclass relations. We illustrate thus the potential of an ontology language which is suit- able for the Life Sciences domain and exhibits an encouraging balance between expressive power and practical feasibility.]]>
We describe a prototype that performs structure-based classification of molecular structures. The software we present implements a sound and com- plete reasoning procedure of a formalism that extends logic programming and builds upon the DLV deductive databases system. We capture a wide range of chemical classes that are not expressible with OWL-based formalisms such as cyclic molecules, saturated molecules and alkanes. In terms of performance, a no- ticeable improvement is observed in comparison with previous approaches. Our evaluation has discovered subsumptions that are missing from the the manually curated ChEBI ontology as well as discrepancies with respect to existing subclass relations. We illustrate thus the potential of an ontology language which is suit- able for the Life Sciences domain and exhibits an encouraging balance between expressive power and practical feasibility.]]> Sun, 02 Dec 2012 06:31:49 GMT /slideshow/ontologybased-classification-of-molecules-a-logic-programming-approach/15450084 magkades@slideshare.net(magkades) Ontology-Based Classification of Molecules: a Logic Programming Approach magkades We describe a prototype that performs structure-based classification of molecular structures. The software we present implements a sound and com- plete reasoning procedure of a formalism that extends logic programming and builds upon the DLV deductive databases system. We capture a wide range of chemical classes that are not expressible with OWL-based formalisms such as cyclic molecules, saturated molecules and alkanes. In terms of performance, a no- ticeable improvement is observed in comparison with previous approaches. Our evaluation has discovered subsumptions that are missing from the the manually curated ChEBI ontology as well as discrepancies with respect to existing subclass relations. We illustrate thus the potential of an ontology language which is suit- able for the Life Sciences domain and exhibits an encouraging balance between expressive power and practical feasibility. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/swat4lsslides-magka-121202063149-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" /> We describe a prototype that performs structure-based classification of molecular structures. The software we present implements a sound and com- plete reasoning procedure of a formalism that extends logic programming and builds upon the DLV deductive databases system. We capture a wide range of chemical classes that are not expressible with OWL-based formalisms such as cyclic molecules, saturated molecules and alkanes. In terms of performance, a no- ticeable improvement is observed in comparison with previous approaches. Our evaluation has discovered subsumptions that are missing from the the manually curated ChEBI ontology as well as discrepancies with respect to existing subclass relations. We illustrate thus the potential of an ontology language which is suit- able for the Life Sciences domain and exhibits an encouraging balance between expressive power and practical feasibility.

Ontology-Based Classification of Molecules: a Logic Programming Approach from Despoina Magka

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0 Classifying Chemicals with Description Graphs and Logic Programming /slideshow/classifying-chemicals-with-description-graphs-and-logic-programming/15313326 slidesowled12-121123061306-phpapp02
OWL 2 is widely used to describe complex objects such as chemical molecules; however, OWL 2 axioms cannot represent `structural' features of chemical entities such as having a ring. A combination of OWL 2, rules and \emph{description graphs} (DGs) has been suggested as a possible solution, but an attempt to apply this formalism in a chemical Semantic Web application has revealed several drawbacks. Based on this experience, we present a radically different approach to modelling complex objects via a novel formalism that we call Description Graph Logic Programs. At the syntactic level, our approach combines DGs, rules, and OWL 2 RL axioms, but we give semantics to our formalism via a translation into logic programs interpreted under stable model semantics. The result is an expressive formalism that is well suited for modelling objects with complex structure, that captures the OWL 2 RL profile, and that thus fits naturally into the Semantic Web landscape. Additionally, we test the practical feasibility of our approach by means of a prototypical implementation which provides encouraging results. ]]>
OWL 2 is widely used to describe complex objects such as chemical molecules; however, OWL 2 axioms cannot represent `structural' features of chemical entities such as having a ring. A combination of OWL 2, rules and \emph{description graphs} (DGs) has been suggested as a possible solution, but an attempt to apply this formalism in a chemical Semantic Web application has revealed several drawbacks. Based on this experience, we present a radically different approach to modelling complex objects via a novel formalism that we call Description Graph Logic Programs. At the syntactic level, our approach combines DGs, rules, and OWL 2 RL axioms, but we give semantics to our formalism via a translation into logic programs interpreted under stable model semantics. The result is an expressive formalism that is well suited for modelling objects with complex structure, that captures the OWL 2 RL profile, and that thus fits naturally into the Semantic Web landscape. Additionally, we test the practical feasibility of our approach by means of a prototypical implementation which provides encouraging results. ]]> Fri, 23 Nov 2012 06:13:05 GMT /slideshow/classifying-chemicals-with-description-graphs-and-logic-programming/15313326 magkades@slideshare.net(magkades) Classifying Chemicals with Description Graphs and Logic Programming magkades OWL 2 is widely used to describe complex objects such as chemical molecules; however, OWL 2 axioms cannot represent `structural' features of chemical entities such as having a ring. A combination of OWL 2, rules and \emph{description graphs} (DGs) has been suggested as a possible solution, but an attempt to apply this formalism in a chemical Semantic Web application has revealed several drawbacks. Based on this experience, we present a radically different approach to modelling complex objects via a novel formalism that we call Description Graph Logic Programs. At the syntactic level, our approach combines DGs, rules, and OWL 2 RL axioms, but we give semantics to our formalism via a translation into logic programs interpreted under stable model semantics. The result is an expressive formalism that is well suited for modelling objects with complex structure, that captures the OWL 2 RL profile, and that thus fits naturally into the Semantic Web landscape. Additionally, we test the practical feasibility of our approach by means of a prototypical implementation which provides encouraging results. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/slidesowled12-121123061306-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" /> OWL 2 is widely used to describe complex objects such as chemical molecules; however, OWL 2 axioms cannot represent `structural' features of chemical entities such as having a ring. A combination of OWL 2, rules and \emph{description graphs} (DGs) has been suggested as a possible solution, but an attempt to apply this formalism in a chemical Semantic Web application has revealed several drawbacks. Based on this experience, we present a radically different approach to modelling complex objects via a novel formalism that we call Description Graph Logic Programs. At the syntactic level, our approach combines DGs, rules, and OWL 2 RL axioms, but we give semantics to our formalism via a translation into logic programs interpreted under stable model semantics. The result is an expressive formalism that is well suited for modelling objects with complex structure, that captures the OWL 2 RL profile, and that thus fits naturally into the Semantic Web landscape. Additionally, we test the practical feasibility of our approach by means of a prototypical implementation which provides encouraging results.

Classifying Chemicals with Description Graphs and Logic Programming from Despoina Magka

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0 Tractable Extensions of the Description Logic EL with Numerical Datatypes /slideshow/slides-ijcar10/15313321 slidesijcar10-121123061249-phpapp02
We consider extensions of the lightweight description logic (DL) EL with numerical datatypes such as naturals, integers, rationals and reals equipped with relations such as equality and inequalities. It is well-known that the main reasoning problems for such DLs are decid- able in polynomial time provided that the datatypes enjoy the so-called convexity property. Unfortunately many combinations of the numerical relations violate convexity, which makes the usage of these datatypes rather limited in practice. In this paper, we make a more fine-grained complexity analysis of these DLs by considering restrictions not only on the kinds of relations that can be used in ontologies but also on their occurrences, such as allowing certain relations to appear only on the left- hand side of the axioms. To this end, we introduce a notion of safety for a numerical datatype with restrictions (NDR) which guarantees tractabil- ity, extend the EL reasoning algorithm to these cases, and provide a complete classification of safe NDRs for natural numbers, integers, ra- tionals and reals.]]>
We consider extensions of the lightweight description logic (DL) EL with numerical datatypes such as naturals, integers, rationals and reals equipped with relations such as equality and inequalities. It is well-known that the main reasoning problems for such DLs are decid- able in polynomial time provided that the datatypes enjoy the so-called convexity property. Unfortunately many combinations of the numerical relations violate convexity, which makes the usage of these datatypes rather limited in practice. In this paper, we make a more fine-grained complexity analysis of these DLs by considering restrictions not only on the kinds of relations that can be used in ontologies but also on their occurrences, such as allowing certain relations to appear only on the left- hand side of the axioms. To this end, we introduce a notion of safety for a numerical datatype with restrictions (NDR) which guarantees tractabil- ity, extend the EL reasoning algorithm to these cases, and provide a complete classification of safe NDRs for natural numbers, integers, ra- tionals and reals.]]> Fri, 23 Nov 2012 06:12:47 GMT /slideshow/slides-ijcar10/15313321 magkades@slideshare.net(magkades) Tractable Extensions of the Description Logic EL with Numerical Datatypes magkades We consider extensions of the lightweight description logic (DL) EL with numerical datatypes such as naturals, integers, rationals and reals equipped with relations such as equality and inequalities. It is well-known that the main reasoning problems for such DLs are decid- able in polynomial time provided that the datatypes enjoy the so-called convexity property. Unfortunately many combinations of the numerical relations violate convexity, which makes the usage of these datatypes rather limited in practice. In this paper, we make a more fine-grained complexity analysis of these DLs by considering restrictions not only on the kinds of relations that can be used in ontologies but also on their occurrences, such as allowing certain relations to appear only on the left- hand side of the axioms. To this end, we introduce a notion of safety for a numerical datatype with restrictions (NDR) which guarantees tractabil- ity, extend the EL reasoning algorithm to these cases, and provide a complete classification of safe NDRs for natural numbers, integers, ra- tionals and reals. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/slidesijcar10-121123061249-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" /> We consider extensions of the lightweight description logic (DL) EL with numerical datatypes such as naturals, integers, rationals and reals equipped with relations such as equality and inequalities. It is well-known that the main reasoning problems for such DLs are decid- able in polynomial time provided that the datatypes enjoy the so-called convexity property. Unfortunately many combinations of the numerical relations violate convexity, which makes the usage of these datatypes rather limited in practice. In this paper, we make a more fine-grained complexity analysis of these DLs by considering restrictions not only on the kinds of relations that can be used in ontologies but also on their occurrences, such as allowing certain relations to appear only on the left- hand side of the axioms. To this end, we introduce a notion of safety for a numerical datatype with restrictions (NDR) which guarantees tractabil- ity, extend the EL reasoning algorithm to these cases, and provide a complete classification of safe NDRs for natural numbers, integers, ra- tionals and reals.

Tractable Extensions of the Description Logic EL with Numerical Datatypes from Despoina Magka

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0 Acyclicity Conditions and their Application to Query Answering in Description Logics /slideshow/slides-kr12/15313318 slideskr12-121123061224-phpapp01
Answering conjunctive queries (CQs) over a set of facts extended with existential rules is a key problem in knowledge representation and databases. This problem can be solved using the chase (aka materialisation) algorithm; however, CQ answering is undecidable for general existential rules, so the chase is not guaranteed to terminate. Several acyclicity conditions provide sufficient conditions for chase termination. In this paper, we present two novel such conditions—modelfaithful acyclicity (MFA) and model-summarising acyclicity (MSA)—that generalise many of the acyclicity conditions known so far in the literature. Materialisation provides the basis for several widely-used OWL 2 DL reasoners. In order to avoid termination problems, many of these systems handle only the OWL 2 RL profile of OWL 2 DL; furthermore, some systems go beyond OWL 2 RL, but they provide no termination guarantees. In this paper we investigate whether various acyclicity conditions can provide a principled and practical solution to these problems. On the theoretical side, we show that query answering for acyclic ontologies is of lower complexity than for general ontologies. On the practical side, we show that many of the commonly used OWL 2 DL ontologies are MSA, and that the facts obtained via materialisation are not too large. Thus, our results suggest that principled extensions to materialisationbased OWL 2 DL reasoners may be practically feasible.]]>
Answering conjunctive queries (CQs) over a set of facts extended with existential rules is a key problem in knowledge representation and databases. This problem can be solved using the chase (aka materialisation) algorithm; however, CQ answering is undecidable for general existential rules, so the chase is not guaranteed to terminate. Several acyclicity conditions provide sufficient conditions for chase termination. In this paper, we present two novel such conditions—modelfaithful acyclicity (MFA) and model-summarising acyclicity (MSA)—that generalise many of the acyclicity conditions known so far in the literature. Materialisation provides the basis for several widely-used OWL 2 DL reasoners. In order to avoid termination problems, many of these systems handle only the OWL 2 RL profile of OWL 2 DL; furthermore, some systems go beyond OWL 2 RL, but they provide no termination guarantees. In this paper we investigate whether various acyclicity conditions can provide a principled and practical solution to these problems. On the theoretical side, we show that query answering for acyclic ontologies is of lower complexity than for general ontologies. On the practical side, we show that many of the commonly used OWL 2 DL ontologies are MSA, and that the facts obtained via materialisation are not too large. Thus, our results suggest that principled extensions to materialisationbased OWL 2 DL reasoners may be practically feasible.]]> Fri, 23 Nov 2012 06:12:24 GMT /slideshow/slides-kr12/15313318 magkades@slideshare.net(magkades) Acyclicity Conditions and their Application to Query Answering in Description Logics magkades Answering conjunctive queries (CQs) over a set of facts extended with existential rules is a key problem in knowledge representation and databases. This problem can be solved using the chase (aka materialisation) algorithm; however, CQ answering is undecidable for general existential rules, so the chase is not guaranteed to terminate. Several acyclicity conditions provide sufficient conditions for chase termination. In this paper, we present two novel such conditions—modelfaithful acyclicity (MFA) and model-summarising acyclicity (MSA)—that generalise many of the acyclicity conditions known so far in the literature. Materialisation provides the basis for several widely-used OWL 2 DL reasoners. In order to avoid termination problems, many of these systems handle only the OWL 2 RL profile of OWL 2 DL; furthermore, some systems go beyond OWL 2 RL, but they provide no termination guarantees. In this paper we investigate whether various acyclicity conditions can provide a principled and practical solution to these problems. On the theoretical side, we show that query answering for acyclic ontologies is of lower complexity than for general ontologies. On the practical side, we show that many of the commonly used OWL 2 DL ontologies are MSA, and that the facts obtained via materialisation are not too large. Thus, our results suggest that principled extensions to materialisationbased OWL 2 DL reasoners may be practically feasible. <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/slideskr12-121123061224-phpapp01-thumbnail.jpg?width=120&height=120&fit=bounds" /> Answering conjunctive queries (CQs) over a set of facts extended with existential rules is a key problem in knowledge representation and databases. This problem can be solved using the chase (aka materialisation) algorithm; however, CQ answering is undecidable for general existential rules, so the chase is not guaranteed to terminate. Several acyclicity conditions provide sufficient conditions for chase termination. In this paper, we present two novel such conditions—modelfaithful acyclicity (MFA) and model-summarising acyclicity (MSA)—that generalise many of the acyclicity conditions known so far in the literature. Materialisation provides the basis for several widely-used OWL 2 DL reasoners. In order to avoid termination problems, many of these systems handle only the OWL 2 RL profile of OWL 2 DL; furthermore, some systems go beyond OWL 2 RL, but they provide no termination guarantees. In this paper we investigate whether various acyclicity conditions can provide a principled and practical solution to these problems. On the theoretical side, we show that query answering for acyclic ontologies is of lower complexity than for general ontologies. On the practical side, we show that many of the commonly used OWL 2 DL ontologies are MSA, and that the facts obtained via materialisation are not too large. Thus, our results suggest that principled extensions to materialisationbased OWL 2 DL reasoners may be practically feasible.

Acyclicity Conditions and their Application to Query Answering in Description Logics from Despoina Magka

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0 Modelling Structured Domains with Description Graphs and Logic Programming /slideshow/modelling-structured-domains-with-description-graphs-and-logic-programming/15313293 slideseswc12-121123061040-phpapp02
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]]> Fri, 23 Nov 2012 06:10:39 GMT /slideshow/modelling-structured-domains-with-description-graphs-and-logic-programming/15313293 magkades@slideshare.net(magkades) Modelling Structured Domains with Description Graphs and Logic Programming magkades <img style="border:1px solid #C3E6D8;float:right;" alt="" src="https://cdn.slidesharecdn.com/ss_thumbnails/slideseswc12-121123061040-phpapp02-thumbnail.jpg?width=120&height=120&fit=bounds" />

Modelling Structured Domains with Description Graphs and Logic Programming from Despoina Magka

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0 https://cdn.slidesharecdn.com/profile-photo-magkades-48x48.jpg?cb=1523527831 Research interests: automated reasoning, knowledge representation, semantic technologies, life sciences, description logics, nonmonotonic reasoning. www.cs.ox.ac.uk/isg/people/despoina.magka/ https://cdn.slidesharecdn.com/ss_thumbnails/9fe07876-fdb6-4458-b9db-a5c0138efd0c-150401133819-conversion-gate01-thumbnail.jpg?width=320&height=320&fit=bounds slideshow/thesisdespoina/46550462 thesis-despoina https://cdn.slidesharecdn.com/ss_thumbnails/jcai-13-slides-131010065936-phpapp01-thumbnail.jpg?width=320&height=320&fit=bounds slideshow/jcai-13slides/27057698 Computing Stable Model... https://cdn.slidesharecdn.com/ss_thumbnails/swat4lsslides-magka-121202063149-phpapp02-thumbnail.jpg?width=320&height=320&fit=bounds slideshow/ontologybased-classification-of-molecules-a-logic-programming-approach/15450084 Ontology-Based Classif...