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Abstract

This thesis is organised as follows: Chapter 2 gives a general introduction to the field of information retrieval, covering its most important aspects. Further, the tasks of distributed and peer-to-peer information retrieval (P2PIR) are introduced, motivating their application and characterising the special challenges that they involve, including a review of existing architectures and search protocols in P2PIR. Finally, chapter 2 presents approaches to evaluating the e ectiveness of both traditional and peer-to-peer IR systems. Chapter 3 contains a detailed account of state-of-the-art information retrieval models and algorithms. This encompasses models for matching queries against document representations, term weighting algorithms, approaches to feedback and associative retrieval as well as distributed retrieval. It thus defines important terminology for the following chapters. The notion of "multi-level association graphs" (MLAGs) is introduced in chapter 4. An MLAG is a simple, graph-based framework that allows to model most of the theoretical and practical approaches to IR presented in chapter 3. Moreover, it provides an easy-to-grasp way of defining and including new entities into IR modeling, such as paragraphs or peers, dividing them conceptually while at the same time connecting them to each other in a meaningful way. This allows for a unified view on many IR tasks, including that of distributed and peer-to-peer search. Starting from related work and a formal defiition of the framework, the possibilities of modeling that it provides are discussed in detail, followed by an experimental section that shows how new insights gained from modeling inside the framework can lead to novel combinations of principles and eventually to improved retrieval effectiveness.

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Footnote

Rez. in: ZfBB 50(2003) H.5, S.295-297 (E. Scheven):"In ihrem Buch »Zeitbegriffe und Zeitcodierungen in allgemeinbibliographischen Datenbanken« entwickelt die Autorin ein theoretisches Modell für ein Zeitretrieval in allgemeinbibliografischen Datenbanken. Dafür untersucht sie die Verwendung von Zeitbegriffen (Epochenbezeichnungen, historiografischen Begriffen) und Zeitcodierungen (Jahreszahlen, Datumsangaben) bei der Indexierung von Dokumenten in allgemeinbibliografischen Datenbanken und deren Retrievalmöglichkeiten. Durch Globalisierung und Internet ist der Zugang zu den Katalogen unterschiedlichster lnstitutionen weit überdie Landesgrenzen hinaus möglich geworden. Dadurch ist der Zwang zur Standardisierung der bibliothekarischen Regeln weltweit verschärft, um Daten-Interoperabilität zu gewährleisten. Hauptziel der Sacherschließung muss immer die optimale Befriedigung der Benutzerbedürfnisse sein. - Kompetente Einführung - Nach einer kurzen geschichtlichen Darstellung der Zeitrechnung an sich und der bibliothekarischen Regelentwicklung wendet sich die Autorin den wichtigsten Sacherschließungswerkzeugen der westlichen WeIt zu, zum einen den beiden internationalen Universalklassifikationen, DDC und UDK, und zum anderen den drei Schlagwortsystemen LCSH, Rameau und SWD,wobei sieden Schwerpunkt auf die verbalen Sacherschließungssysteme legt. LCSH, Rameau und SWD mit RSWK werden kompetent und ausführlich in 164 von 316 Seiten mit ihrer Entwicklungsgeschichte und ihren Unterschieden dargestellt. Jutta Frommeyer ist hier eine gute vergleichende Einführung in die großen verbalen Sacherschließungssysteme gelungen und zwar nicht nur für Anfänger, sondern auch für praxis-erfahrene Sacherschließer. Die Darstellung von Zeitaspekten nach LCSH kann nach sechs verschiedenen Varianten erfolgen. Es gibt keine allgemeinen subdivisions für Zeitangaben. Rameau stimmt in seiner Struktur mit den LCSH überein, weicht aber bei der Indexierung bezüglich der subdivisions von den LCSH ab. Rameau hat eine allgemein zu verwendende Liste (subdivision) mit ca. 40 Unterteilungen für den Zeitaspekt. Nach RSWK wird der Zeitaspekt durch so genannte Zeitschlagwörter wiedergegeben, die wie auch bestimmte Formalschlagwörter durch Jahreszahlen erweitert werden können. Der im Dokument behandelte Zeitabschnitt wird für die Beschlagwortung herangezogen. Vorgegebene Zeituntergliederungen für bestimmte Themenbereiche wie bei LCSH und Rameau gibt es bei RSWK nicht. Zwischen den Schlagwortsystemen gibt es unterschiedliche Indexierungsregeln, wann ein Zeitschlagwort benutzt werden soll oder nicht.

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