2004
Conference article
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A unifying framework for flexible information access in taxonomy-based sources
Tzitzikas Y, Meghini C, Spyratos NA taxonomy-based source consists of a taxonomy and a database storing objects that are indexed in terms of the taxonomy. For this kind of sources, we describe a flexible interaction scheme that allows users to retrieve the objects of interest without having to be familiar with the terms of the taxonomy or with the supported query language. Specifically we describe an interaction manager whose functionality unifies several well-known interaction schemes including query by example, answer enlargement/reduction, query relaxation/ restriction, index relaxation/contraction, feedback and adaptation mechanisms.
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2004
Conference article
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Querying articulated sources
Meghini C, Tzitzikas YIn this study we address the problem of answering queries over information sources storing objects which are indexed by terms arranged in a taxonomy. We examine query languages of different expressivity and sources with different kinds of taxonomies. In the simplest kind, the taxonomy includes just term-to-term subsumption links. This case is used as a basis for further developments, in which we consider taxonomies consisting of term-to-queries links. An algorithm for query evaluation is presented for this kind of taxonomies, and it is shown that the addition of negation to the query language leads to intractability. Finally, query-to-query taxonomies are considered.
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2004
Conference article
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Towards a generalized interaction scheme for information access
Tzitzikas Y, Meghini C, Spyratos NWe introduce the formal framework of a generalized interaction scheme for information access between users and information sources. Within this framework we describe an interaction manager which supports more complex interaction schemes than those that are supported by existing systems, including: query by example, answer enlargement/reduction, query relaxation/restriction, index relaxation/contraction, 'relevance' feedback, and adaptation facilities. We give the foundations of this interaction manager from a mathematical point of view, in terms of an abstract view of an information source.
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2006
Journal article
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A unified interaction scheme for information sources
Tzitzikas Y, Meghini C, Spyratos NCommonly, for retrieving the desired information from an information source (knowledge base or information base), the user has to use the query language that is provided by the system. This is a big barrier for many ordinary users and the resulting interaction style is rather inflexible. In this paper we give the theoretical foundations of an interaction scheme that allows users to retrieve the objects of interest without having to be familiar with the conceptual schema of the source or with the supported query language. Specifically, we describe an interaction manager that provides a quite flexible interaction scheme by unifying several well-known interaction schemes. Furthermore, we show how this scheme can be applied to taxonomy-based sources by providing all needed algorithms and reporting their computational complexity.Source: JOURNAL OF INTELLIGENT INFORMATION SYSTEMS, vol. 26 (issue 1), pp. 75-93
DOI: 10.1007/s10844-006-5452-0Metrics:
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Journal of Intelligent Information Systems
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2006
Conference article
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Abduction for extending incomplete information sources
Meghini C, Tzitzikas Y, Spyratos NThe extraction of information from a source containing term-classified objects is plagued with uncertainty, due, among other things, to the possible incompleteness of the source index. To overcome this incompleteness, the study proposes to expand the index of the source, in a way that is as reasonable as possible with respect to the original classification of objects. By equating reasonableness with logical implication, the sought expansion turns out to be an explanation of the index, captured by abduction. We study the general problem of query evaluation on the extended information source, providing a polynomial time algorithm which tackles the general case, in which no hypothesis is made on the structure of the taxonomy. We then specialize the algorithm for two well-know structures: DAGs and trees, showing that each specialization results in a more efficient query evaluation.DOI: 10.1007/11752912_28Metrics:
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doi.org
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2007
Conference article
Open Access
Computing intensions of digital library collections
Meghini C, Spyratos NWe model a Digital Library as a formal context in which objects are documents and attributes are terms describing documents contents. A formal concept is very close to the notion of a collection: the concept extent is the extension of the collection; the concept intent consists of a set of terms, the collection intension. The collection intension can be viewed as a simple conjunctive query which evaluates precisely to the extension. However, for certain collections no concept may exist, in which case the concept that best approximates the extension must be used. In so doing, we may end up with a too imprecise concept, in case too many documents denoted by the intension are outside the extension. We then look for a more precise intension by exploring 3 different query languages: conjunctive queries with negation; disjunctions of negationfree conjunctive queries; and disjunctions of conjunctive queries with negation. We show that a precise description can always be found in one of these languages for any set of documents. However, when disjunction is introduced, uniqueness of the solution is lost. In order to deal with this problem, we define a preferential criterion on queries, based on the conciseness of their expression. We then show that minimal queries are hard to find in the last 2 of the three languages above.DOI: 10.1007/978-3-540-70901-5_5Metrics:
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www.nmis.isti.cnr.it
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2003
Conference article
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An Abduction-based Method for Index Relaxation in Taxonomy-based Sources
Meghini C, Tzitzikas Y, Spiratos NThe extraction of information from a source containing termclassified objects is plagued with uncertainty. In the present paper we deal with this uncertainty in a qualitative way. We view an information source as an agent, operating according to an open world philosophy. The agent knows some facts, but is aware that there could be other facts, compatible with the known ones, that might hold as well, although they are not captured for lack of knowledge. These facts are, indeed, ossibilities. We view possibilities as explanations and resort to abduction in order to define precisely the ossibilities that we want our system to be able to handle. We introduce an operation that extends a taxonomy-based source with possibilities, and then study the property of this operation from a mathematical point of view.DOI: 10.1007/978-3-540-45138-9_53Metrics:
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doi.org
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2003
Conference article
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Ostensive Automatic Schema Mapping for Taxonomy-based Peer-to-Peer Systems
Tzitzikas Y, Meghini CThis paper considers Peer-to-Peer systems in which peers employ taxonomies for describing the contents of their objects and for formulating semantic-based queries to the other peers of the system. As each peer can use its own taxonomy, peers are equipped with intertaxonomy mappings in order to carry out the required translation tasks. As these systems are ad-hoc, the peers should be able to create or revise these mappings on demand and at run-time. For this reason, we introduce an ostensive data-driven method for automatic mapping and specialize it for the case of taxonomies.
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2003
Conference article
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Query Evaluation in Peer-to-Peer Networks of Taxonomy-based Sources
Meghini C, Tzitzikas YWe consider the problem of query evaluation in Peer-to-Peer (P2P) systems that support semantic-based retrieval services.We confine ourselves to the case where the peers employ taxonomies for describing the contents of the objects, and articulations, i.e. inter-taxonomy mappings, for bridging the inevitable naming, granularity and contextual heterogeneities that may exist between the taxonomies of the sources. We identify two basic query evaluation approaches: one based on query rewriting, the other based on direct query evaluation. For each approach we present a centralized and a decentralized algorithm for carrying out the query evaluation task. Finally, we present a qualitative comparison of these algorithms and discuss further optimizations. Correctness of the algorithms presented is based on a mathematical analysis of the problem.
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2008
Journal article
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Synthesizing monadic predicates
Meghini C, Spyratos NWe study the problem of determining a concise, quantifier-free monadic predicate for a given set of objects in a given interpretation. We ad- dress both DNF and CNF predicates, as well as important sub-languages thereof. The problem is formalized as the search of a minimal element in a set of predicates equipped with a binary relation. We show that the problem has always a solution, that finding a minimal solution is always hard, but much harder when neither the given set of objects nor its com- plement are the extent of a formal concept (in the sense of Formal Concept Analysis).Source: JOURNAL OF LOGIC AND COMPUTATION, vol. 18 (issue 6), pp. 831-847
DOI: 10.1093/logcom/exn006Metrics:
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Journal of Logic and Computation
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2010
Conference article
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A functionality perspective on digital library interoperability
Meghini C, Athanasopoulos G, Fox E, Ioannidis Y, Kakaletris G, Manola N, Rauber A, Soergel DDigital Library (DL) interoperability requires addressing a variety of issues associated with functionality. We report on the analysis and solutions identified by the Functionality Working Group of the DL.org project during its deliberations on DL interoperability. Ultimately, we hope that work based on our perspective will lead to improved architectures and software, as well as to greater interoperability, for next-generation DL systems.DOI: 10.1007/978-3-642-15464-5_43Metrics:
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2010
Conference article
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Modelling digital libraries based on logic
Meghini C, Spyratos N, Sugibuchi TWe present a data model for digital libraries supporting identification, description and discovery of digital objects. The model is formalized as a first-order theory, certain models of which correspond to the intuitive notion of digital library. Our main objective is to lay the foundations for the design of an API offering the above functionality. Additionally, we use our formal framework to discuss the adequacy of the Resource Description Framework with respect to the requirements of digital libraries.DOI: 10.1007/978-3-642-15464-5_2Project(s): Advanced Search Services and Enhanced Technological Solutions for the European Digital Library
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2007
Conference article
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Viewing Collections as Abstractions
Meghini C, Spyratos NDigital Libraries collections are an abstraction mechanism, endowed with an extension and an intension, similarly to predicates in logic. The extension of a collection is the set of objects that are members of the collection at a given point in time, while the intension is a description of the meaning of the collection, that is the peculiar property that the members of the collection possess and that distinguishes the collection from other collections. This view reconciles the many types of collections found in Digital Library systems, but raises several problems, among which how to automatically derive the intension from a given extension. This problem must be solved e.g. for the creation of a collection from a set of documents. We outline basic results on the problem and then show how intensions can be exploited for carrying out basic tasks on collections, establishing a connection between Digital Library management and data integration.
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2007
Conference article
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CASPAR project and the validation of digital preservation techniques
Meghini C, Et AThe CASPAR project is an Integrated Project part funded by the European Union. It seeks to develop tools and techniques to support the preservation of digitally encoded information. Underpinning the project are the themes of the OAIS Reference Model, and also of validation of that model and of the tools which CASPAR develops. The immediate challenges are from the domains of science, performing arts and cultural heritage. In each of these areas we look at a variety of preservation scenarios in which there are changes to hardware, software, environment and the knowledgebase of the Designated Community. It is believed that CASPAR will be relevant to the preservation not only of these domains but also for many other, perhaps all, types of digital information. CASPAR started in April 2006 and has developed a validation strategy which should be broadly applicable to projects which claim to be able to support digital preservation efforts. The presentation will report on this validation approach.
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