Inconsistency-tolerant semantics for description logics
22 Sep 2010-pp 103-117
TL;DR: It is shown that, if the notion of repair studied in databases is used, inconsistency-tolerant query answering is intractable, even for the simplest form of queries.
Abstract: We address the problem of dealing with inconsistencies in Description Logic (DL) knowledge bases. Our general goal is both to study DL semantical frameworks which are inconsistency-tolerant, and to devise techniques for answering unions of conjunctive queries posed to DL knowledge bases under such inconsistency-tolerant semantics. Our work is inspired by the approaches to consistent query answering in databases, which are based on the idea of living with inconsistencies in the database, but trying to obtain only consistent information during query answering, by relying on the notion of database repair. We show that, if we use the notion of repair studied in databases, inconsistency-tolerant query answering is intractable, even for the simplest form of queries. Therefore, we study different variants of the repair-based semantics, with the goal of reaching a good compromise between expressive power of the semantics and computational complexity of inconsistency-tolerant query answering.
Citations
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TL;DR: MASTRO is a Java tool for ontology-based data access (OBDA) developed at Sapienza Universita di Roma and at the Free University of Bozen-Bolzano that provides optimized algorithms for answering expressive queries, as well as features for intensional reasoning and consistency checking.
Abstract: In this paper we present MASTRO, a Java tool for ontology-based data access (OBDA) developed at Sapienza Universita di Roma and at the Free University of Bozen-Bolzano. MASTRO manages OBDA systems in which the ontology is specified in DL-Lite A,id, a logic of the DL-Lite family of tractable Description Logics specifically tailored to ontology-based data access, and is connected to external JDBC enabled data management systems through semantic mappings that associate SQL queries over the external data to the elements of the ontology. Advanced forms of integrity constraints, which turned out to be very useful in practical applications, are also enabled over the ontologies. Optimized algorithms for answering expressive queries are provided, as well as features for intensional reasoning and consistency checking. MASTRO provides a proprietary API, an OWLAPI compatible interface, and a plugin for the Protege 4 ontology editor. It has been successfully used in several projects carried out in collaboration with important organizations, on which we briefly comment in this paper.
282 citations
Cites background from "Inconsistency-tolerant semantics fo..."
...Theoretical results at the basis of the approach we want to implement can be found in [21]....
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31 Jul 2015
TL;DR: A brief introduction to ontology-mediated query answering using description logic (DL) ontologies, with a focus on DLs for which query answering scales polynomially in the size of the data, as these are best suited for applications requiring large amounts of data.
Abstract: Recent years have seen an increasing interest in ontology-mediated query answering, in which the semantic knowledge provided by an ontology is exploited when querying data. Adding an ontology has several advantages (e.g. simplifying query formulation, integrating data from different sources, providing more complete answers to queries), but it also makes the query answering task more difficult. In this chapter, we give a brief introduction to ontology-mediated query answering using description logic (DL) ontologies. Our focus will be on DLs for which query answering scales polynomially in the size of the data, as these are best suited for applications requiring large amounts of data. We will describe the challenges that arise when evaluating different natural types of queries in the presence of such ontologies, and we will present algorithmic solutions based upon two key concepts, namely, query rewriting and saturation. We conclude the chapter with an overview of recent results and active areas of ongoing research.
145 citations
Proceedings Article•
03 Aug 2013TL;DR: This paper proposes two new families of inconsistency-tolerant semantics which approximate the CQA semantics from above and from below and converge to it in the limit, and shows a general tractability result for all known first-order rewritable ontology languages.
Abstract: A robust system for ontology-based data access should provide meaningful answers to queries even when the data conflicts with the ontology. This can be accomplished by adopting an inconsistency-tolerant semantics, with the consistent query answering (CQA) semantics being the most prominent example. Unfortunately, query answering under the CQA semantics has been shown to be computationally intractable, even when extremely simple ontology languages are considered. In this paper, we address this problem by proposing two new families of inconsistency-tolerant semantics which approximate the CQA semantics from above and from below and converge to it in the limit. We study the data complexity of conjunctive query answering under these new semantics, and show a general tractability result for all known first-order rewritable ontology languages. We also analyze the combined complexity of query answering for ontology languages of the DL-Lite family.
107 citations
Proceedings Article•
22 Jul 2012TL;DR: In order to be able to handle arbitrary conjunctive queries, a novel inconsistency-tolerant semantics is proposed and it is shown that under this semantics, first-order expressibility is always guaranteed.
Abstract: Consistent query answering is a standard approach for producing meaningful query answers when data is inconsistent. Recent work on consistent query answering in the presence of ontologies has shown this problem to be intractable in data complexity even for ontologies expressed in lightweight description logics. In order to better understand the source of this intractability, we investigate the complexity of consistent query answering for simple ontologies consisting only of class subsumption and class disjointness axioms. We show that for conjunctive queries with at most one quantified variable, the problem is first-order expressible; for queries with at most two quantified variables, the problem has polynomial data complexity but may not be first-order expressible; and for three quantified variables, the problem may become co-NP-hard in data complexity. For queries having at most two quantified variables, we further identify a necessary and sufficient condition for first-order expressibility. In order to be able to handle arbitrary conjunctive queries, we propose a novel inconsistency-tolerant semantics and show that under this semantics, first-order expressibility is always guaranteed. We conclude by extending our positive results to DL-Lite ontologies without inverse.
107 citations
Cites background or methods from "Inconsistency-tolerant semantics fo..."
...As mentioned in the introduction, it was shown in (Lembo et al. 2010) that consistent instance checking in DL-Lite is co-NP-hard in data complexity, which means in particular that consistent rewritings need not exist....
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...To obtain positive results for arbitrary conjunctive queries, we propose a novel inconsistency-tolerant semantics which is a sound approximation of the consistent query answering semantics (and a finer approximation than the approximate semantics proposed in (Lembo et al. 2010))....
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...In (Lembo et al. 2010), four different inconsistency-tolerant query answering semantics (AR, IAR, CAR, ICAR) were studied for DL-Lite, and it was shown that CQ answering is coNP-hard in data complexity for AR and CAR semantics, and first-order expressible for the IAR and ICAR semantics (Lembo et al....
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...In (Lembo et al. 2010), four different inconsistency-tolerant query answering semantics (AR, IAR, CAR, ICAR) were studied for DL-Lite, and it was shown that CQ answering is coNP-hard in data complexity for AR and CAR semantics, and first-order expressible for the IAR and ICAR semantics (Lembo et…...
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...Consistent query answering for the DL-Lite family of lightweight DLs was investigated in (Lembo et al. 2010; 2011)....
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TL;DR: This work proposes a different repair-based semantics, and shows that query answering under the new semantics is first-order rewritable in OBDA, even if the ontology is expressed in one of the most expressive members of the DL-Lite family.
98 citations
References
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01 Jan 2003
TL;DR: The Description Logic Handbook as mentioned in this paper provides a thorough account of the subject, covering all aspects of research in this field, namely: theory, implementation, and applications, and can also be used for self-study or as a reference for knowledge representation and artificial intelligence courses.
Abstract: Description logics are embodied in several knowledge-based systems and are used to develop various real-life applications. Now in paperback, The Description Logic Handbook provides a thorough account of the subject, covering all aspects of research in this field, namely: theory, implementation, and applications. Its appeal will be broad, ranging from more theoretically oriented readers, to those with more practically oriented interests who need a sound and modern understanding of knowledge representation systems based on description logics. As well as general revision throughout the book, this new edition presents a new chapter on ontology languages for the semantic web, an area of great importance for the future development of the web. In sum, the book will serve as a unique resource for the subject, and can also be used for self-study or as a reference for knowledge representation and artificial intelligence courses.
5,644 citations
TL;DR: It is shown that, for the DLs of the DL-Lite family, the usual DL reasoning tasks are polynomial in the size of the TBox, and query answering is LogSpace in thesize of the ABox, which is the first result ofPolynomial-time data complexity for query answering over DL knowledge bases.
Abstract: We propose a new family of description logics (DLs), called DL-Lite, specifically tailored to capture basic ontology languages, while keeping low complexity of reasoning. Reasoning here means not only computing subsumption between concepts and checking satisfiability of the whole knowledge base, but also answering complex queries (in particular, unions of conjunctive queries) over the instance level (ABox) of the DL knowledge base. We show that, for the DLs of the DL-Lite family, the usual DL reasoning tasks are polynomial in the size of the TBox, and query answering is LogSpace in the size of the ABox (i.e., in data complexity). To the best of our knowledge, this is the first result of polynomial-time data complexity for query answering over DL knowledge bases. Notably our logics allow for a separation between TBox and ABox reasoning during query evaluation: the part of the process requiring TBox reasoning is independent of the ABox, and the part of the process requiring access to the ABox can be carried out by an SQL engine, thus taking advantage of the query optimization strategies provided by current database management systems. Since even slight extensions to the logics of the DL-Lite family make query answering at least NLogSpace in data complexity, thus ruling out the possibility of using on-the-shelf relational technology for query processing, we can conclude that the logics of the DL-Lite family are the maximal DLs supporting efficient query answering over large amounts of instances.
1,482 citations
"Inconsistency-tolerant semantics fo..." refers background or methods in this paper
...It follows from the results in [4, 13] that query answering in DL-LiteA is inACo, which is a complexity class contained in PTIME, and therefore is tractable in data complexity....
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...In this paper, we will consider DLs specifically tailored towards ODBA, in particular DLs of the DL-Lite family [4], where query answering can be done efficiently with respect to the size of the ABox....
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...We recall that DL-Litecore is the least expressive logic in the DL-Lite family, as it only allows for concept expressions of the form C ::= A|∃R|∃R−, and for TBox assertions of the form C1 v C2, C1 v ¬C2 (for more details, see [4])....
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...We now provide some details about the DL DL-LiteA, a member of the DL-Lite family [4]....
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TL;DR: This paper presents a new ontology language, based on Description Logics, that is particularly suited to reason with large amounts of instances and a novel mapping language that is able to deal with the so-called impedance mismatch problem.
Abstract: Many organizations nowadays face the problem of accessing existing data sources by means of flexible mechanisms that are both powerful and efficient. Ontologies are widely considered as a suitable formal tool for sophisticated data access. The ontology expresses the domain of interest of the information system at a high level of abstraction, and the relationship between data at the sources and instances of concepts and roles in the ontology is expressed by means of mappings. In this paper we present a solution to the problem of designing effective systems for ontology-based data access. Our solution is based on three main ingredients. First, we present a new ontology language, based on Description Logics, that is particularly suited to reason with large amounts of instances. The second ingredient is a novel mapping language that is able to deal with the so-called impedance mismatch problem, i.e., the problem arising from the difference between the basic elements managed by the sources, namely data, and the elements managed by the ontology, namely objects. The third ingredient is the query answering method, that combines reasoning at the level of the ontology with specific mechanisms for both taking into account the mappings and efficiently accessing the data at the sources.
884 citations
"Inconsistency-tolerant semantics fo..." refers background in this paper
...From the fact that the algorithm Compute-IAR-Repair(K) runs in polynomial time and from tractability of UCQ entailment in DL-LiteA [13], the claim follows....
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...It follows from the results in [4, 13] that query answering in DL-LiteA is inACo, which is a complexity class contained in PTIME, and therefore is tractable in data complexity....
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...We are particularly interested in using DLs for the so-called “ontology-based data access” [13] (ODBA), where a DL TBox acts as an ontology used to access a set of data sources....
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Book•
01 Dec 2005
TL;DR: Semantic Acceleration Helping Realize the Semantic Web Vision or "The Practical Web", research/Academic track.
546 citations
01 Jan 2005
TL;DR: In this paper, the authors present an approach for using the Semantic Web for e-Science: Inspiration, Incubation, Irritation, and Semantic Acceleration Helping Realize the semantic Web Vision or "The Practical Web".
Abstract: Invited Paper.- Using the Semantic Web for e-Science: Inspiration, Incubation, Irritation.- Semantic Acceleration Helping Realize the Semantic Web Vision or "The Practical Web".- Semantic Web Public Policy Challenges: Privacy, Provenance, Property and Personhood.- Research/Academic Track.- Constructing Complex Semantic Mappings Between XML Data and Ontologies.- Stable Model Theory for Extended RDF Ontologies.- Towards a Formal Verification of OWL-S Process Models.- Web Service Composition with Volatile Information.- A Large Scale Taxonomy Mapping Evaluation.- RDF Entailment as a Graph Homomorphism.- RitroveRAI: A Web Application for Semantic Indexing and Hyperlinking of Multimedia News.- Querying Ontologies: A Controlled English Interface for End-Users.- Semantic Browsing of Digital Collections.- Decentralized Case-Based Reasoning for the Semantic Web.- Finding and Ranking Knowledge on the Semantic Web.- Choreography in IRS-III - Coping with Heterogeneous Interaction Patterns in Web Services.- Bootstrapping Ontology Alignment Methods with APFEL.- A Strategy for Automated Meaning Negotiation in Distributed Information Retrieval.- On Applying the AGM Theory to DLs and OWL.- A General Diagnosis Method for Ontologies.- Graph-Based Inferences in a Semantic Web Server for the Cartography of Competencies in a Telecom Valley.- Ontology Design Patterns for Semantic Web Content.- Guidelines for Benchmarking the Performance of Ontology Management APIs.- Semantically Rich Recommendations in Social Networks for Sharing, Exchanging and Ranking Semantic Context.- On Partial Encryption of RDF-Graphs.- Seven Bottlenecks to Workflow Reuse and Repurposing.- On Logical Consequence for Collections of OWL Documents.- A Framework for Handling Inconsistency in Changing Ontologies.- Preferential Reasoning on a Web of Trust.- Resolution-Based Approximate Reasoning for OWL DL.- Reasoning with Multi-version Ontologies: A Temporal Logic Approach.- Piggy Bank: Experience the Semantic Web Inside Your Web Browser.- BRAHMS: A WorkBench RDF Store and High Performance Memory System for Semantic Association Discovery.- A Template-Based Markup Tool for Semantic Web Content.- Representing Web Service Policies in OWL-DL.- Information Modeling for End to End Composition of Semantic Web Services.- Searching Dynamic Communities with Personal Indexes.- RUL: A Declarative Update Language for RDF.- Ontologies Are Us: A Unified Model of Social Networks and Semantics.- OMEN: A Probabilistic Ontology Mapping Tool.- On the Properties of Metamodeling in OWL.- A Bayesian Network Approach to Ontology Mapping.- Ontology Change Detection Using a Version Log.- RelExt: A Tool for Relation Extraction from Text in Ontology Extension.- Containment and Minimization of RDF/S Query Patterns.- A String Metric for Ontology Alignment.- An Ontological Framework for Dynamic Coordination.- Introducing Autonomic Behaviour in Semantic Web Agents.- Combining RDF and Part of OWL with Rules: Semantics, Decidability, Complexity.- Benchmarking Database Representations of RDF/S Stores.- Towards Imaging Large-Scale Ontologies for Quick Understanding and Analysis.- Automatic Evaluation of Ontologies (AEON).- A Method to Combine Linguistic Ontology-Mapping Techniques.- Debugging OWL-DL Ontologies: A Heuristic Approach.- Rapid Benchmarking for Semantic Web Knowledge Base Systems.- Using Triples for Implementation: The Triple20 Ontology-Manipulation Tool.- A Little Semantic Web Goes a Long Way in Biology.- Provenance-Based Validation of E-Science Experiments.- Industrial Track.- Semantic Service Integration for Water Resource Management.- Towards a Killer App for the Semantic Web.- Enterprise Architecture Reference Modeling in OWL/RDF.- MediaCaddy - Semantic Web Based On-Demand Content Navigation System for Entertainment.- LKMS - A Legal Knowledge Management System Exploiting Semantic Web Technologies.- Definitions Management: A Semantics-Based Approach for Clinical Documentation in Healthcare Delivery.- Ubiquitous Service Finder Discovery of Services Semantically Derived from Metadata in Ubiquitous Computing.- Ontological Approach to Generating Personalized User Interfaces for Web Services.- On Identifying Knowledge Processing Requirements.- An Application of Semantic Web Technologies to Situation Awareness.- Task Knowledge Based Retrieval for Service Relevant to Mobile User's Activity.- Supporting Rule System Interoperability on the Semantic Web with SWRL.- Automated Business-to-Business Integration of a Logistics Supply Chain Using Semantic Web Services Technology.- A Semantic Search Engine for the International Relation Sector.- Gnowsis Adapter Framework: Treating Structured Data Sources as Virtual RDF Graphs.- Do Not Use This Gear with a Switching Lever! Automotive Industry Experience with Semantic Guides.- The Concept Object Web for Knowledge Management.- Semantic Web Challenge.- The Personal Publication Reader.- DynamicView: Distribution, Evolution and Visualization of Research Areas in Computer Science.- Oyster - Sharing and Re-using Ontologies in a Peer-to-Peer Community.- The FungalWeb Ontology: Semantic Web Challenges in Bioinformatics and Genomics.- CONFOTO: A Semantic Browsing and Annotation Service for Conference Photos.
530 citations