Hybrid index maintenance for contiguous inverted lists

Index maintenance strategies employed by dynamic text retrieval systems based on inverted files can be divided into two categories: merge-based and in-place update strategies. Within each category, individual update policies can be distinguished based on whether they store their on-disk posting lists in a contiguous or in a discontiguous fashion. Contiguous inverted lists, in general, lead to higher query performance, by minimizing the disk seek overhead at query time, while discontiguous inverted lists lead to higher update performance, requiring less effort during index maintenance operations. In this paper, we focus on retrieval systems with high query load, where the on-disk posting lists have to be stored in a contiguous fashion at all times. We discuss a combination of re-merge and in-place index update, called Hybrid Immediate Merge. The method performs strictly better than the re-merge baseline policy used in our experiments, as it leads to the same query performance, but substantially better update performance. The actual time savings achievable depend on the size of the text collection being indexed; a larger collection results in greater savings. In our experiments, variations of Hybrid Immediate Merge were able to reduce the total index update overhead by up to 73% compared to the re-merge baseline.

An Evaluation of Synchronous Co-operative Distance Learning in the Field: The Importance of Instructional Design

This paper describes an empirical field study on synchronous co-operative distance learning carried out in a large software company. The goal of the study was to make an analysis of the co-operative learning process. Seven small groups consisting of three participants each completed an introductory web-based training about the Linux operating system. Four short synchronous co-operative phases were embedded in the web-based training. An analysis of the group discourses showed a large variation in the learning processes that took place in the different groups. This finding can be explained by the ill-defined instructional design on which the co-operative learning process was based. The methodology used in the present study enables both a detailed analysis of the learning process as well as for the development of task-specific process models that can be used for the re-design of instruction. Une evaluation de l’apprentissage coopératif synchrone sur le champs: l’importance d’un schéma

d’instruction. Cet article décrit une étude de cas empirique sur un enseignement À distance synchrone et coopératif menée dans une grande compagnie productrice de software. Let but de l’étude était de faire une analyse du processus d’apprentissage coopératif. 7 petits groupes comprenant chacun 3 participants ont suivi une formation introductive basée sur le Web sur le systéme opératoire Linux. 4 courtes phases synchrones coopératives étaient comprises dans l’apprentissage basé sur le Web. Une analyse des discourse des groupes a montré de grandes variations dans le processus d’apprentissage qui a eu lieu dans les différents groupes. Ces résultats peuvent être expliqués par le fait que l’élaboration de cette instruction sur laquelle le processus d’apprentissage coopératif étant basé était mal définie. La méthodologie utilisée dans l’étude présente permet À la fois une analyse détaillée du processus d’apprentissage aussi bien que le développement de modéles de tÂches spécifiques que peuvent être utilisés pour la re-élaboration de l’instruction. Ein Feldversuch mit kooperativem synchronem E-Learning: Die Bedeuting des Instruktionsdesigns. In diesem Beitrag wird eine empirische Feldstudie in synchronem kooperativen Distance Learning beschrieben, die in einer

grossen Softwarefirma angestellt wurde. Ziel der Studie war, einen kooperativen Lernprozess zu analysieren. Sieben kleine, aus drei Teilnehmern bestehende Gruppen führten jeweils ein web-basiertes Einführungsprogramm über das Linux Betriebssystem durch. In das web-basierte Training waren vier kurze synchrone kooperative Phasen eingebaut. Eine Analyse der Gruppendiskurse ergab eine grosse Varianz der in den einzelnen Gruppen stattfindenden Lernprozesse. Diese Befund Kann durch den unklaren Unterrichtsentwurf, auf den der kooperative Lernprozess gegründet war, erklärt werden. Die in der angeführten Studie verwendete Methodologie liefert sowohl eine detaillierte Analyse des Lernprozesses als auch die für die Weiterentwicklung des Lernprogramms benötigten aufgabenspezifischen Modelle.     

The role of national archives in constructing national master narratives in Europe

This article analyses the role of national archives for the construction of national master narratives. It starts off by discussing the different origins of national archives, the merits of talking about proto-national archives and the importance of the French revolution for establishing the modern national archive system. It goes on to highlight the difficulties of historians with obtaining access to the archives in the nineteenth century. The importance of archives in authenticating and legitimating the authority of historical work meant that archives became increasingly important for the professionalization of history writing. As history writing saw one of its prime tasks in legitimating the nation-state, archives soon occupied an important position for nation-building projects. They got involved in editing sources regarded as being of national importance, and they played a role in projects of national pedagogy. The article also charts efforts to centralize archives at the national level which resulted in failure almost everywhere. Nevertheless, whilst archives were clearly important for imperial and also subnational projects, it was the national archives that captured the imagination of nation-states in the nineteenth and twentieth centuries. Despite the importance of national archives, the articles goes on to argue that it is striking that most national master narratives in the modern period were not based on archival work.