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The Vector Space Model (VSM) is probably the most widely used model for retrieving information from text collections (and recently from over other kinds of corpi). Assuming this model, we study the problem of finding the best query that "names" (or describes) a given (unordered or ordered) set of objects. We formulate several variations of this problem and we provide methods and algorithms for solving them. [ABSTRACT FROM AUTHOR]

Intelligibility, evolution and emulation are some of the key notions for digital information preservation. In this paper we define formally these notions on the basis of modules and inter-module dependencies. Subsequently, we discuss how we can handle the evolution of modules and dependencies. This work can be exploited for building advanced preservation information systems and registries. [ABSTRACT FROM AUTHOR]

The notion of dependency is ubiquitous. This paper approaches this notion from the perspective of digital information preservation. At first, an abstract notion of module and dependency is introduced. Subsequently, and for building preservation information systems, the notion of profile is proposed as a gnomon for deciding representation information adequacy (during input) and intelligibility (during output). Subsequently some general dependency management services for identifying and filling gaps during input and output are described and analyzed (also described as protocols that could be used in the communication between a preservation information system and information consumers and providers). [ABSTRACT FROM AUTHOR]

A faceted taxonomy is a set of taxonomies each describing the application domain from a different (preferably orthogonal) point of view. CTCA is an algebra that allows specifying the set of meaningful compound terms (meaningful conjunctions of terms) over a faceted taxonomy in a flexible and efficient manner. However, taxonomy updates may turn a CTCA expression e ill-formed and may turn the compound terms specified by e to no longer reflect the domain knowledge originally expressed in e. This paper shows how we can revise e after a taxonomy update and reach an expression e′ that is both well-formed and whose semantics (compound terms defined) is as close as possible to the semantics of the original expression e before the update. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

According to the recently emerged, trialogical learning (TL) paradigm, learners are collaboratively developing shared objects of activity in a systematic fashion. In this paper we propose a basic learning scenario according to the TL paradigm. With this scenario as gnomon, we elaborate the technical issues that are raised for supporting it and we propose a flexible novel method for defining various aspects of the group knowledge. [ABSTRACT FROM AUTHOR]

Understanding a large schema without the assistance of persons already familiar with it (and its associated applications), is a hard and very time consuming task that occurs very frequently in reverse engineering and in information integration. In this paper we describe a novel method that can aid the understanding and the visualization of very large ER diagrams that is inspired by the link analysis techniques that are used in Web Searching. Specifically, this method takes as input an ER diagram and returns a smaller (top-k) diagram that consists of the major entity and relationship types of the initial diagram. Concerning the drawing of the resulting top-k graphs in the 2D space, we propose a force-directed placement algorithm especially adapted for ER diagrams. Specifically, we describe and analyze experimentally two different force models and various configurations. The experimental evaluation on large diagrams of real world applications proved the effectiveness of this technique. [ABSTRACT FROM AUTHOR]

The Compound Term Composition Algebra (CTCA) is an algebra with four algebraic operators, whose composition can be used to specify the meaningful (valid) compound terms (conjunctions of terms) in a given faceted taxonomy in an efficient and flexible manner. The "positive" operations allow the derivation of valid compound terms through the declaration of a small set of valid compound terms. The "negative" operations allow the derivation of valid compound terms through the declaration of a small set of invalid compound terms. In this paper, we formally define the model-theoretic semantics of the operations and the closed-world assumptions adopted in each operation. We prove that CTCA is monotonic with respect to both valid and invalid compound terms, meaning that the valid and invalid compound terms of a subexpression are not invalidated by a larger expression. We show that CTCA cannot be directly represented in Description Logics. However, we show how we could design a metasystem on top of Description Logics in order to implement this algebra. Keywords: Faceted Taxonomies, Semantics, Description Logics. [ABSTRACT FROM AUTHOR]

A materialized faceted taxonomy is an information source where the objects of interest are indexed according to a faceted taxonomy. This paper shows how from a materialized faceted taxonomy, we can mine an expression of the Compound Term Composition Algebra that specifies exactly those compound terms that have non-empty interpretation. The mined expressions can be used for encoding compactly (and subsequently reusing) the domain knowledge that is stored in existing materialized faceted taxonomies. Furthermore, expression mining is very crucial for reorganizing taxonomy-based sources which were not initially designed according to a clear faceted approach (like the directories of Google and Yahoo!), so as to have a semantically clear, and compact faceted structure. We analyze this problem and we give an analytical description of all algorithms needed for expression mining. [ABSTRACT FROM AUTHOR]

Building very big taxonomies is a laborious task vulnerable to errors and management/scalability deficiencies. FASTAXON is a system for building very big taxonomies in a quick, flexible and scalable manner that is based on the faceted classification paradigm [4] and the Compound Term Composition Algebra [5]. We sketch the architecture and the functioning of this system and we report our experiences from using this system in real applications. [ABSTRACT FROM AUTHOR]