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Practical Reasoning for Expressive Description Logics
, 1999
"... . Description Logics (DLs) are a family of knowledge representation formalisms mainly characterised by constructors to build complex concepts and roles from atomic ones. Expressive role constructors are important in many applications, but can be computationally problematical. We present an algorithm ..."
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Cited by 354 (65 self)
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. Description Logics (DLs) are a family of knowledge representation formalisms mainly characterised by constructors to build complex concepts and roles from atomic ones. Expressive role constructors are important in many applications, but can be computationally problematical. We present an algorithm that decides satis ability of the DL ALC extended with transitive and inverse roles, role hierarchies, and qualifying number restrictions. Early experiments indicate that this algorithm is wellsuited for implementation. Additionally, we show that ALC extended with just transitive and inverse roles is still in PSpace. Finally, we investigate the limits of decidability for this family of DLs.
Linking data to ontologies
 J. on Data Semantics
, 2008
"... 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 t ..."
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Cited by 198 (73 self)
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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 ontologybased 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 socalled 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.
Practical reasoning for very expressive description logics
 Journal of the Interest Group in Pure and Applied Logics 8
, 2000
"... Description Logics (DLs) are a family of knowledge representation formalisms mainly characterised by constructors to build complex concepts and roles from atomic ones. Expressive role constructors are important in many applications, but can be computationally problematical. We present an algorithm t ..."
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Cited by 185 (22 self)
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Description Logics (DLs) are a family of knowledge representation formalisms mainly characterised by constructors to build complex concepts and roles from atomic ones. Expressive role constructors are important in many applications, but can be computationally problematical. We present an algorithm that decides satisfiability of the DL ALC extended with transitive and inverse roles and functional restrictions with respect to general concept inclusion axioms and role hierarchies; early experiments indicate that this algorithm is wellsuited for implementation. Additionally, we show that ALC extended with just transitive and inverse roles is still in PSpace. We investigate the limits of decidability for this family of DLs, showing that relaxing the constraints placed on the kinds of roles used in number restrictions leads to the undecidability of all inference problems. Finally, we describe a number of optimisation techniques that are crucial in obtaining implementations of the decision procedures, which, despite the hight worstcase complexity of the problem, exhibit good performance with reallife problems. 1
Distributed Description Logics: Assimilating Information from Peer Sources
, 2003
"... Due to the availability on the Internet of a wide variety of sources of information on closely related topics, the problem of providing seamless, integrated access to such sources has become (again) a major research challenge. Although this problem has been studied for several decades, especiall ..."
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Cited by 158 (14 self)
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Due to the availability on the Internet of a wide variety of sources of information on closely related topics, the problem of providing seamless, integrated access to such sources has become (again) a major research challenge. Although this problem has been studied for several decades, especially in the database community, there is a need for a more refined approach in those cases where the original sources maintain their own independent view of the world. In particular, we motivate with examples the utility of directed noninjective mappings between the individuals in the domains of multiple Information Sources.
Reasoning with Individuals for the Description Logic SHIQ
, 2000
"... While there has been a great deal of work on the development of reasoning algorithms for expressive description logics, in most cases only Tbox reasoning is considered. In this paper we present an algorithm for combined Tbox and Abox reasoning in the SHIQ description logic. This algorithm is of part ..."
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Cited by 153 (33 self)
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While there has been a great deal of work on the development of reasoning algorithms for expressive description logics, in most cases only Tbox reasoning is considered. In this paper we present an algorithm for combined Tbox and Abox reasoning in the SHIQ description logic. This algorithm is of particular interest as it can be used to decide the problem of (database) conjunctive query containment w.r.t. a schema. Moreover, the realisation of an efficient implementation should be relatively straightforward as it can be based on an existing highly optimised implementation of the Tbox algorithm in the FaCT system.
Data Integration under Integrity Constraints
 Information Systems
, 2002
"... Data integratio n systemspro vide accessto a seto fhetero  geneo us, auto no mo us data so urces thro ugh a so called glo bal schema. There are basically two appro aches fo r designing a data integratio n system. In the glo balcentric appro ach,o ne defines the elementso f the glo bal schema as v ..."
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Cited by 115 (22 self)
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Data integratio n systemspro vide accessto a seto fhetero  geneo us, auto no mo us data so urces thro ugh a so called glo bal schema. There are basically two appro aches fo r designing a data integratio n system. In the glo balcentric appro ach,o ne defines the elementso f the glo bal schema as viewso ver the so urces, whereas in the lo calcentric appro ach, o e characterizes the so rces as viewso ver theglo al schema. It is well kno wn that pro cessing queries in the latter appro ach is similar to query answering with inc o plete infoC atio , and, therefo9 is a c o plex task. On theo ther hand, it is a co mmo no pinio n that query pro cessing is much easier in the fo rmer appro ach. In this paper we sho w the surprising result that, when theglo al schema is expressed in the relatio al mo del with integrity c o straints, eveno f simple types, the pr o lemo f inco6 plete info rmatio n implicitly arises, making querypro cessing di#cult in the glo alcentric approC h as well. We thenfo cuso n glo al schemas with key andfo eign key co straints, which represents a situat io which is veryco#=W in practice, and we illustrate techniques fo e#ectively answering queries po sed to the data integratio n system in this case. 1
Learning Object Identification Rules for Information Integration
 Information Systems
, 2001
"... When integrating information from multiple websites, the same data objects can exist in inconsistent text formats across sites, making it di#cult to identify matching objects using exact text match. We have developed an object identification system called Active Atlas, which compares the objects& ..."
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Cited by 111 (9 self)
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When integrating information from multiple websites, the same data objects can exist in inconsistent text formats across sites, making it di#cult to identify matching objects using exact text match. We have developed an object identification system called Active Atlas, which compares the objects' shared attributes in order to identify matching objects. Certain attributes are more important for deciding if a mapping should exist between two objects. Previous methods of object identification have required manual construction of object identification rules or mapping rules for determining the mappings between objects. This manual process is time consuming and errorprone.
The Complexity of Reasoning with Cardinality Restrictions and Nominals in Expressive Description Logics
 JOURNAL OF ARTIFICIAL INTELLIGENCE RESEARCH
, 2000
"... We study the complexity of the combination of the Description Logics ALCQ and ALCQI with a terminological formalism based on cardinality restrictions on concepts. These combinations can naturally be embedded into C², the two variable fragment of predicate logic with counting quantifiers, which yi ..."
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Cited by 77 (0 self)
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We study the complexity of the combination of the Description Logics ALCQ and ALCQI with a terminological formalism based on cardinality restrictions on concepts. These combinations can naturally be embedded into C², the two variable fragment of predicate logic with counting quantifiers, which yields decidability in NExpTime. We show that this approach leads to an optimal solution for ALCQI, as ALCQI with cardinality restrictions has the same complexity as C² (NExpTimecomplete). In contrast, we show that for ALCQ, the problem can be solved in ExpTime. This result is obtained by a reduction of reasoning with cardinality restrictions to reasoning with the (in general weaker) terminological formalism of general axioms for ALCQ extended with nominals . Using the same reduction, we show that, for the extension of ALCQI with nominals, reasoning with general axioms is a NExpTimecomplete problem. Finally, we sharpen this result and show that pure concept satisfiability for A...
Information integration: Conceptual modeling and reasoning support
 In Proceedings of the International Conference on Cooperative Information Systems
, 1998
"... Information Integration is one of the core problems in cooperative information systems. We argue that two critical factors for the design and maintenance of applications requiring Information Integration are conceptual modeling of the domain, and reasoning support over the conceptual representation. ..."
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Cited by 76 (9 self)
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Information Integration is one of the core problems in cooperative information systems. We argue that two critical factors for the design and maintenance of applications requiring Information Integration are conceptual modeling of the domain, and reasoning support over the conceptual representation. In particular, we present a general architecture for Information Integration that explicitly includes a conceptual representation of the application. We illustrate how the architecture can express several integration settings and existing systems. We provide various arguments in favor of the conceptual level in the architecture and of automated reasoning over the conceptual representation. Finally, we present a specific proposal of an integration system which realizes the general architecture and is equipped with decidable reasoning procedures. 1.
FaCT and iFaCT
 Proceedings of the International Workshop on Description Logics, Linköping, Sweden
, 1999
"... scription Logic (DL) classier which has been implemented as a testbed for a sound and complete tableaux satis ability/subsumption testing algorithm. FaCT's novelty lies in its relatively expressive logic and its highly optimised implementation of the tableaux algorithm. iFaCT is an extension ..."
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Cited by 73 (7 self)
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scription Logic (DL) classier which has been implemented as a testbed for a sound and complete tableaux satis ability/subsumption testing algorithm. FaCT's novelty lies in its relatively expressive logic and its highly optimised implementation of the tableaux algorithm. iFaCT is an extension of FaCT that supports reasoning with inverse roles. The resulting logic is particularly interesting as it no longer has the nite model property. Language The logics implemented in FaCT and iFaCT are both based on ALC R, an extension of ALC to include transitive roles [Sattler, 1996]. For compactness, this logic will be called S (due to its relationship with the proposition multimodal logic S4 (m) [Schild, 1991]). FaCT extends S with a hierarchy of roles and functional roles (attributes) to give SHF, while iFaCT adds inverse roles to give SHIF. The constructs used by the two logics are described in Figure 1, where A is an atomic concept, R and S are roles, C and D are concepts, R is the set of transitive role names and F is the set of functional role names (there is an additional restriction that R and F must be disjoint). The meaning of concepts and roles is given by an interpretation I = ( I