Query containment under constraints is the problem of determining whether the result of one query... more Query containment under constraints is the problem of determining whether the result of one query is contained in the result of another query for every database satisfying a given set of constraints. This problem is of particular importance in information integration and warehousing where, in addition to the constraints derived from the source schemas and the global schema, inter-schema constraints can be used to specify relationships between objects in different schemas. A theoretical framework for tackling this problem using the DLR logic has been established, and in this paper we show how the framework can be extended to a practical decision procedure. The proposed technique is to extend DLR with an Abox (a set of assertions about named individuals and tuples), and to transform query subsumption problems into DLR Abox satisfiability problems. We then show how such problems can be decided, via a reification transformation, using a highly optimised reasoner for the SHIQ description...
Classification is a key ontology reasoning task. Several highly-optimised OWL reasoners are desig... more Classification is a key ontology reasoning task. Several highly-optimised OWL reasoners are designed for different fragments of OWL 2. Combining these delegate reasoners to classify one ontology gives potential benefits, but these may be offset by overheads or redundant subsumption tests. In this paper, we show that with the help of the atomic decomposition, a known ontology partition approach, these redundant subsumption tests can be avoided. We design and implement our classification algorithms and empirically evaluate them.
Comparing the importance of axioms in ontologies is an essential task in a variety of application... more Comparing the importance of axioms in ontologies is an essential task in a variety of applications such as ontology repair and inconsistency management. It guides the choice of axioms to remain in the ontology or which should prevail when a conflict arises. While evaluating the importance of an axiom is difficult, there are different approaches to stratify ontologies by criteria that act as proxies for importance. However, there is little work about how these methods are related and their adequacy considering different applications. In this work, we evaluate specificity and modularity-based stratification approaches, and work towards understanding how they relate. We compare empirically the result of five stratification methods over a corpus of real-world ontologies. In particular, we investigate correlations between their rankings and their ability to distinguish axioms.
Reasoning with SROIQ(D), the logic that underpins the popular Web Ontology Language (OWL), has a ... more Reasoning with SROIQ(D), the logic that underpins the popular Web Ontology Language (OWL), has a high worst case complexity (N2Exptime). Decomposing the ontology into modules prior to classification, and then classifying the composites one-by-one, has been suggested as a way to mitigate this complexity in practice. Modular reasoning is currently motivated by the potential for reducing the hardness of subsumption tests, reducing the number of necessary subsumption tests and integrating efficient delegate reasoners. To date, we have only a limited idea of what we can expect from modularity as an optimisation technique. We present sound evidence that, while the impact of subsumption testing is significant only for a small number of ontologies across a popular collection of 330 ontologies (BioPortal), modularity has a generally positive effect on subsumption test hardness (2-fold mean reduction in our sample). More than 50% of the tests did not change in hardness at all, however, and we observed large differences across reasoners. We conclude (1) that, in general, optimisations targeting subsumption test hardness need to be well motivated because of their comparatively modest overall impact on classification time and (2) that employing modularity for optimisation should not be motivated by beneficial effects on subsumption test hardness alone.
OWL 2 DL is a complex logic with reasoning problems that have a high worst case complexity. Moder... more OWL 2 DL is a complex logic with reasoning problems that have a high worst case complexity. Modern reasoners perform mostly very well on naturally occurring ontologies of varying sizes and complexity. This performance is achieved through a suite of complex optimisations (with complex interactions) and elaborate engineering. While the formal basis of the core reasoner procedures are well understood, many optimisations are less so, and most of the engineering details (and their possible effect on reasoner correctness) are unreviewed by anyone but the reasoner developer. Thus, it is unclear how much confidence should be placed in the correctness of implemented reasoners. To date, there is no principled, correctness unit test-like suite for simple language features and, even if there were, it is unclear that passing such a suite would say much about correctness on naturally occurring ontologies. This problem is not merely theoretical: Divergence in behaviour (thus known bugginess of implementations) has been observed in the OWL Reasoner Evaluation (ORE) contests to the point where a simple, majority voting procedure has been put in place to resolve disagreements. In this paper, we present a new technique for finding and resolving reasoner disagreement. We use justifications to cross check disagreements. Some cases are resolved automatically, others need to be manually verified. We evaluate the technique on a corpus of naturally occurring ontologies and a set of popular reasoners. We successfully identify several correctness bugs across different reasoners, identify causes for most of these, and generate appropriate bug reports and patches to ontologies to work around the bug.
Very expressive Description Logics in the SH family have worst case complexity ranging from EXPTI... more Very expressive Description Logics in the SH family have worst case complexity ranging from EXPTIME to double NEXPTIME. In spite of this, they are very popular with modellers and serve as the foundation of the Web Ontology Language (OWL), a W3C standard. Highly optimised reasoners handle a wide range of naturally occurring ontologies with relative ease, albeit with some pathological cases. A recent optimisation trend has been modular reasoning, that is, breaking the ontology into hopefully easier subsets with a hopefully smaller overall reasoning time (see MORe and Chainsaw for prominent examples). However, it has been demonstrated that subsets of an OWL ontology may be harder-even much harder-than the whole ontology. This introduces the risk that modular approaches might have even more severe pathological cases than the normal monolithic ones. In this paper, we analyse a number of ontologies from the BioPortal repository in order to isolate cases where random subsets are harder than the whole. For such cases, we then examine whether the module nearest to the random subset also exhibits the pathological behaviour.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 2005
We show how state-of-the-art Semantic Web technology can be used in e-Science, in particular to a... more We show how state-of-the-art Semantic Web technology can be used in e-Science, in particular to automate the classification of proteins in biology. We show that the resulting classification was of comparable quality to one performed by a human expert, and how investigations using the classified data even resulted in the discovery of significant information that had previously been overlooked, leading to the identification of a possible drug-target.
Motivated by medical terminology applications, we investigate the decidability of an expressive a... more Motivated by medical terminology applications, we investigate the decidability of an expressive and prominent description logic (DL), SHIQ, extended with role inclusion axioms of the form R • S˙ T. It is well known that a naive such extension leads to undecidability, and thus we restrict our attention to axioms of the form R • S˙ R or S • R˙ R, which is the most important form of axioms in the applications that motivated this extension. Surprisingly, this extension is still undecidable. However, it turns out that by restricting our attention further to acyclic sets of such axioms, we regain decidability. We present a tableau-based decision procedure for this DL and report on its implementation, which promises to behave well in practice and provides important additional functionality in a medical terminology application.
The Family History Knowledge Base (FHKB) was presented at OWLED in 2008. The FHKB uses a rich obj... more The Family History Knowledge Base (FHKB) was presented at OWLED in 2008. The FHKB uses a rich object property hierarchy, including many OWL 2 features, to derive many entailments on some 450 individuals representing the Stevens family. In the ABox, only parent relationships and some sibling relationships (either isSisterOf or isBrotherOf) are asserted. Using a sparse assertion of brother or sister relationships, together with information about gender, other sibling relationships should be able to be inferred. The inability to do this in OWL has been described as the 'Man-Man' problem, and various workarounds have been discussed. We describe a new solution to this issue, implemented in the reasoner FaCT++. This solution allows to capture axioms such as 'My male siblings are my brothers', and we have added them to the FHKB. The number of entailments about, for instance, sibling relationships increases significantly without increasing the number of asserted facts about members of the Stevens family.
Abstract. The canonical standard description logic reasoning service is classification, that is, ... more Abstract. The canonical standard description logic reasoning service is classification, that is, the generation of the set of atomic subsumptions which are entailed by some ontology. While this consequence relation is well defined and finite, there is significant variance in the composition of that set. For example, it is common (in tools and in discussion) to exclude some tautologies (eg, A⊑, A⊑ A). While for many purposes such divergences are harmless, there are many for which precision about what appears in the classification is essential, for ...
Ontologies are set to play a key rôle in the "Semantic Web" by providing a source of shared and p... more Ontologies are set to play a key rôle in the "Semantic Web" by providing a source of shared and precisely defined terms that can be used in descriptions of web resources. Reasoning over such descriptions will be essential if web resources are to be more accessible to automated processes. SHOQ(D) is an expressive description logic equipped with named individuals and concrete datatypes which has almost exactly the same expressive power as the latest web ontology languages (e.g., OIL and DAML+OIL). We present sound and complete reasoning services for this logic.
Automated acquisition (learning) of ontologies from data has attracted research interest because ... more Automated acquisition (learning) of ontologies from data has attracted research interest because it can complement manual, expensive construction of ontologies. We investigate the problem of General Terminology Induction in OWL, i.e. acquiring general, expressive TBox axioms (hypotheses) from an ABox (data). We define novel measures designed to rigorously evaluate the quality of hypotheses while respecting the standard semantics of OWL. We propose an informed, data-driven algorithm that constructs class expressions for hypotheses in OWL and guarantees completeness. We empirically evaluate the quality measures on two corpora of ontologies and run a case study with a domain expert to gain insight into applicability of the measures and acquired hypotheses. The results show that the measures capture different quality aspects and not only correct hypotheses can be interesting.
The past 25 years have seen many attempts to introduce defeasible-reasoning capabilities into a d... more The past 25 years have seen many attempts to introduce defeasible-reasoning capabilities into a description logic setting. Many, if not most, of these attempts are based on preferential extensions of description logics, with a significant number of these, in turn, following the so-called KLM approach to defeasible reasoning initially advocated for propositional logic by Kraus, Lehmann, and Magidor. Each of these attempts has its own aim of investigating particular constructions and variants of the (KLM-style) preferential approach. Here our aim is to provide a comprehensive study of the formal foundations of preferential defeasible reasoning for description logics in the KLM tradition. We start by investigating a notion of defeasible subsumption in the spirit of defeasible conditionals as studied by Kraus, Lehmann, and Magidor in the propositional case. In particular, we consider a natural and intuitive semantics for defeasible subsumption, and we investigate KLM-style syntactic pro...
We extend description logics (DLs) with non-monotonic reasoning features. We start by investigati... more We extend description logics (DLs) with non-monotonic reasoning features. We start by investigating a notion of defeasible subsumption in the spirit of defeasible conditionals as studied by Kraus, Lehmann and Magidor in the propositional case. In particular, we consider a natural and intuitive semantics for defeasible subsumption, and investigate KLM-style syntactic properties for both preferential and rational subsumption. Our contribution includes two representation results linking our semantic constructions to the set of preferential and rational properties considered. Besides showing that our semantics is appropriate, these results pave the way for more effective decision procedures for defeasible reasoning in DLs. Indeed, we also analyse the problem of non-monotonic reasoning in DLs at the level of entailment and present an algorithm for the computation of rational closure of a defeasible ontology. Importantly, our algorithm relies completely on classical entailment and shows t...
Description logics are a family of knowledge representation formalisms that are descended from se... more Description logics are a family of knowledge representation formalisms that are descended from semantic networks and frames via the system KL-ONE. During the last decade, it has been shown that the important reasoning problems (like subsumption and satisfiability) in a great variety of description logics can be decided using tableau-like algorithms. This is not very surprising since description logics have turned out to be closely related to propositional modal logics and logics of programs (such as propositional dynamic logic), for which tableau procedures have been quite successful. Nevertheless, due to different underlying intuitions and applications, most description logics differ significantly from run-of-the-mill modal and program logics. Consequently, the research on tableau algorithms in description logics led to new techniques and results, which are, however, also of interest for modal logicians. In this article, we will focus on three features that play an important rôle in description logics (number restrictions, terminological axioms, and role constructors), and show how they can be taken into account by tableau algorithms.
We present an ExpTime decision procedure for the full µ-Calculus (including converse programs) ex... more We present an ExpTime decision procedure for the full µ-Calculus (including converse programs) extended with nominals and a universal program, thus devising a new, highly expressive ExpTime logic. The decision procedure is based on tree automata, and makes explicit the problems caused by nominals and how to overcome them. Roughly speaking, we show how to reason in a logic lacking the tree model property using techniques for logics with the tree model property. The contribution of the paper is twofold: we extend the family of ExpTime logics, and we present a technique to reason in the presence of nominals.
We present a procedure for deciding (database) query containment under constraints. The technique... more We present a procedure for deciding (database) query containment under constraints. The technique is to extend the logic ÄÊ with an ABox, and to transform query subsumption problems into ÄÊ ABox satisfiability problems. Such problems can then be decided, via a reification transformation, using a highly optimised reasoner for the ËÀÁÉ description logic. We use a simple example to support our hypothesis that this procedure will work well with realistic problems.
Description logics class of knowledge representation formalisms r Descended from structured inher... more Description logics class of knowledge representation formalisms r Descended from structured inheritance networks [Brachman 78]. r Tried to overcome ambiguities in semantic networks and frames that were due to their lack of a formal semantics. r Restriction to a small set of "epistemologically adequate" operators for defining concepts (classes). r Importance of well-defined basic inference procedures: subsumption and instance problem.
Query containment under constraints is the problem of determining whether the result of one query... more Query containment under constraints is the problem of determining whether the result of one query is contained in the result of another query for every database satisfying a given set of constraints. This problem is of particular importance in information integration and warehousing where, in addition to the constraints derived from the source schemas and the global schema, inter-schema constraints can be used to specify relationships between objects in different schemas. A theoretical framework for tackling this problem using the DLR logic has been established, and in this paper we show how the framework can be extended to a practical decision procedure. The proposed technique is to extend DLR with an Abox (a set of assertions about named individuals and tuples), and to transform query subsumption problems into DLR Abox satisfiability problems. We then show how such problems can be decided, via a reification transformation, using a highly optimised reasoner for the SHIQ description...
Classification is a key ontology reasoning task. Several highly-optimised OWL reasoners are desig... more Classification is a key ontology reasoning task. Several highly-optimised OWL reasoners are designed for different fragments of OWL 2. Combining these delegate reasoners to classify one ontology gives potential benefits, but these may be offset by overheads or redundant subsumption tests. In this paper, we show that with the help of the atomic decomposition, a known ontology partition approach, these redundant subsumption tests can be avoided. We design and implement our classification algorithms and empirically evaluate them.
Comparing the importance of axioms in ontologies is an essential task in a variety of application... more Comparing the importance of axioms in ontologies is an essential task in a variety of applications such as ontology repair and inconsistency management. It guides the choice of axioms to remain in the ontology or which should prevail when a conflict arises. While evaluating the importance of an axiom is difficult, there are different approaches to stratify ontologies by criteria that act as proxies for importance. However, there is little work about how these methods are related and their adequacy considering different applications. In this work, we evaluate specificity and modularity-based stratification approaches, and work towards understanding how they relate. We compare empirically the result of five stratification methods over a corpus of real-world ontologies. In particular, we investigate correlations between their rankings and their ability to distinguish axioms.
Reasoning with SROIQ(D), the logic that underpins the popular Web Ontology Language (OWL), has a ... more Reasoning with SROIQ(D), the logic that underpins the popular Web Ontology Language (OWL), has a high worst case complexity (N2Exptime). Decomposing the ontology into modules prior to classification, and then classifying the composites one-by-one, has been suggested as a way to mitigate this complexity in practice. Modular reasoning is currently motivated by the potential for reducing the hardness of subsumption tests, reducing the number of necessary subsumption tests and integrating efficient delegate reasoners. To date, we have only a limited idea of what we can expect from modularity as an optimisation technique. We present sound evidence that, while the impact of subsumption testing is significant only for a small number of ontologies across a popular collection of 330 ontologies (BioPortal), modularity has a generally positive effect on subsumption test hardness (2-fold mean reduction in our sample). More than 50% of the tests did not change in hardness at all, however, and we observed large differences across reasoners. We conclude (1) that, in general, optimisations targeting subsumption test hardness need to be well motivated because of their comparatively modest overall impact on classification time and (2) that employing modularity for optimisation should not be motivated by beneficial effects on subsumption test hardness alone.
OWL 2 DL is a complex logic with reasoning problems that have a high worst case complexity. Moder... more OWL 2 DL is a complex logic with reasoning problems that have a high worst case complexity. Modern reasoners perform mostly very well on naturally occurring ontologies of varying sizes and complexity. This performance is achieved through a suite of complex optimisations (with complex interactions) and elaborate engineering. While the formal basis of the core reasoner procedures are well understood, many optimisations are less so, and most of the engineering details (and their possible effect on reasoner correctness) are unreviewed by anyone but the reasoner developer. Thus, it is unclear how much confidence should be placed in the correctness of implemented reasoners. To date, there is no principled, correctness unit test-like suite for simple language features and, even if there were, it is unclear that passing such a suite would say much about correctness on naturally occurring ontologies. This problem is not merely theoretical: Divergence in behaviour (thus known bugginess of implementations) has been observed in the OWL Reasoner Evaluation (ORE) contests to the point where a simple, majority voting procedure has been put in place to resolve disagreements. In this paper, we present a new technique for finding and resolving reasoner disagreement. We use justifications to cross check disagreements. Some cases are resolved automatically, others need to be manually verified. We evaluate the technique on a corpus of naturally occurring ontologies and a set of popular reasoners. We successfully identify several correctness bugs across different reasoners, identify causes for most of these, and generate appropriate bug reports and patches to ontologies to work around the bug.
Very expressive Description Logics in the SH family have worst case complexity ranging from EXPTI... more Very expressive Description Logics in the SH family have worst case complexity ranging from EXPTIME to double NEXPTIME. In spite of this, they are very popular with modellers and serve as the foundation of the Web Ontology Language (OWL), a W3C standard. Highly optimised reasoners handle a wide range of naturally occurring ontologies with relative ease, albeit with some pathological cases. A recent optimisation trend has been modular reasoning, that is, breaking the ontology into hopefully easier subsets with a hopefully smaller overall reasoning time (see MORe and Chainsaw for prominent examples). However, it has been demonstrated that subsets of an OWL ontology may be harder-even much harder-than the whole ontology. This introduces the risk that modular approaches might have even more severe pathological cases than the normal monolithic ones. In this paper, we analyse a number of ontologies from the BioPortal repository in order to isolate cases where random subsets are harder than the whole. For such cases, we then examine whether the module nearest to the random subset also exhibits the pathological behaviour.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 2005
We show how state-of-the-art Semantic Web technology can be used in e-Science, in particular to a... more We show how state-of-the-art Semantic Web technology can be used in e-Science, in particular to automate the classification of proteins in biology. We show that the resulting classification was of comparable quality to one performed by a human expert, and how investigations using the classified data even resulted in the discovery of significant information that had previously been overlooked, leading to the identification of a possible drug-target.
Motivated by medical terminology applications, we investigate the decidability of an expressive a... more Motivated by medical terminology applications, we investigate the decidability of an expressive and prominent description logic (DL), SHIQ, extended with role inclusion axioms of the form R • S˙ T. It is well known that a naive such extension leads to undecidability, and thus we restrict our attention to axioms of the form R • S˙ R or S • R˙ R, which is the most important form of axioms in the applications that motivated this extension. Surprisingly, this extension is still undecidable. However, it turns out that by restricting our attention further to acyclic sets of such axioms, we regain decidability. We present a tableau-based decision procedure for this DL and report on its implementation, which promises to behave well in practice and provides important additional functionality in a medical terminology application.
The Family History Knowledge Base (FHKB) was presented at OWLED in 2008. The FHKB uses a rich obj... more The Family History Knowledge Base (FHKB) was presented at OWLED in 2008. The FHKB uses a rich object property hierarchy, including many OWL 2 features, to derive many entailments on some 450 individuals representing the Stevens family. In the ABox, only parent relationships and some sibling relationships (either isSisterOf or isBrotherOf) are asserted. Using a sparse assertion of brother or sister relationships, together with information about gender, other sibling relationships should be able to be inferred. The inability to do this in OWL has been described as the 'Man-Man' problem, and various workarounds have been discussed. We describe a new solution to this issue, implemented in the reasoner FaCT++. This solution allows to capture axioms such as 'My male siblings are my brothers', and we have added them to the FHKB. The number of entailments about, for instance, sibling relationships increases significantly without increasing the number of asserted facts about members of the Stevens family.
Abstract. The canonical standard description logic reasoning service is classification, that is, ... more Abstract. The canonical standard description logic reasoning service is classification, that is, the generation of the set of atomic subsumptions which are entailed by some ontology. While this consequence relation is well defined and finite, there is significant variance in the composition of that set. For example, it is common (in tools and in discussion) to exclude some tautologies (eg, A⊑, A⊑ A). While for many purposes such divergences are harmless, there are many for which precision about what appears in the classification is essential, for ...
Ontologies are set to play a key rôle in the "Semantic Web" by providing a source of shared and p... more Ontologies are set to play a key rôle in the "Semantic Web" by providing a source of shared and precisely defined terms that can be used in descriptions of web resources. Reasoning over such descriptions will be essential if web resources are to be more accessible to automated processes. SHOQ(D) is an expressive description logic equipped with named individuals and concrete datatypes which has almost exactly the same expressive power as the latest web ontology languages (e.g., OIL and DAML+OIL). We present sound and complete reasoning services for this logic.
Automated acquisition (learning) of ontologies from data has attracted research interest because ... more Automated acquisition (learning) of ontologies from data has attracted research interest because it can complement manual, expensive construction of ontologies. We investigate the problem of General Terminology Induction in OWL, i.e. acquiring general, expressive TBox axioms (hypotheses) from an ABox (data). We define novel measures designed to rigorously evaluate the quality of hypotheses while respecting the standard semantics of OWL. We propose an informed, data-driven algorithm that constructs class expressions for hypotheses in OWL and guarantees completeness. We empirically evaluate the quality measures on two corpora of ontologies and run a case study with a domain expert to gain insight into applicability of the measures and acquired hypotheses. The results show that the measures capture different quality aspects and not only correct hypotheses can be interesting.
The past 25 years have seen many attempts to introduce defeasible-reasoning capabilities into a d... more The past 25 years have seen many attempts to introduce defeasible-reasoning capabilities into a description logic setting. Many, if not most, of these attempts are based on preferential extensions of description logics, with a significant number of these, in turn, following the so-called KLM approach to defeasible reasoning initially advocated for propositional logic by Kraus, Lehmann, and Magidor. Each of these attempts has its own aim of investigating particular constructions and variants of the (KLM-style) preferential approach. Here our aim is to provide a comprehensive study of the formal foundations of preferential defeasible reasoning for description logics in the KLM tradition. We start by investigating a notion of defeasible subsumption in the spirit of defeasible conditionals as studied by Kraus, Lehmann, and Magidor in the propositional case. In particular, we consider a natural and intuitive semantics for defeasible subsumption, and we investigate KLM-style syntactic pro...
We extend description logics (DLs) with non-monotonic reasoning features. We start by investigati... more We extend description logics (DLs) with non-monotonic reasoning features. We start by investigating a notion of defeasible subsumption in the spirit of defeasible conditionals as studied by Kraus, Lehmann and Magidor in the propositional case. In particular, we consider a natural and intuitive semantics for defeasible subsumption, and investigate KLM-style syntactic properties for both preferential and rational subsumption. Our contribution includes two representation results linking our semantic constructions to the set of preferential and rational properties considered. Besides showing that our semantics is appropriate, these results pave the way for more effective decision procedures for defeasible reasoning in DLs. Indeed, we also analyse the problem of non-monotonic reasoning in DLs at the level of entailment and present an algorithm for the computation of rational closure of a defeasible ontology. Importantly, our algorithm relies completely on classical entailment and shows t...
Description logics are a family of knowledge representation formalisms that are descended from se... more Description logics are a family of knowledge representation formalisms that are descended from semantic networks and frames via the system KL-ONE. During the last decade, it has been shown that the important reasoning problems (like subsumption and satisfiability) in a great variety of description logics can be decided using tableau-like algorithms. This is not very surprising since description logics have turned out to be closely related to propositional modal logics and logics of programs (such as propositional dynamic logic), for which tableau procedures have been quite successful. Nevertheless, due to different underlying intuitions and applications, most description logics differ significantly from run-of-the-mill modal and program logics. Consequently, the research on tableau algorithms in description logics led to new techniques and results, which are, however, also of interest for modal logicians. In this article, we will focus on three features that play an important rôle in description logics (number restrictions, terminological axioms, and role constructors), and show how they can be taken into account by tableau algorithms.
We present an ExpTime decision procedure for the full µ-Calculus (including converse programs) ex... more We present an ExpTime decision procedure for the full µ-Calculus (including converse programs) extended with nominals and a universal program, thus devising a new, highly expressive ExpTime logic. The decision procedure is based on tree automata, and makes explicit the problems caused by nominals and how to overcome them. Roughly speaking, we show how to reason in a logic lacking the tree model property using techniques for logics with the tree model property. The contribution of the paper is twofold: we extend the family of ExpTime logics, and we present a technique to reason in the presence of nominals.
We present a procedure for deciding (database) query containment under constraints. The technique... more We present a procedure for deciding (database) query containment under constraints. The technique is to extend the logic ÄÊ with an ABox, and to transform query subsumption problems into ÄÊ ABox satisfiability problems. Such problems can then be decided, via a reification transformation, using a highly optimised reasoner for the ËÀÁÉ description logic. We use a simple example to support our hypothesis that this procedure will work well with realistic problems.
Description logics class of knowledge representation formalisms r Descended from structured inher... more Description logics class of knowledge representation formalisms r Descended from structured inheritance networks [Brachman 78]. r Tried to overcome ambiguities in semantic networks and frames that were due to their lack of a formal semantics. r Restriction to a small set of "epistemologically adequate" operators for defining concepts (classes). r Importance of well-defined basic inference procedures: subsumption and instance problem.
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Papers by Uli Sattler