Mobile Databases: a Selection of Open Issues and Research Directions

International audienceThis paper reports on the main results of a specific action on mobile databases conducted by CNRS in France from October 2001 to December 2002. The objective of this action was to review the state of progress in mobile databases and identify major research directions for the French database community. Rather than provide a survey of all important issues in mobile databases, this paper gives an outline of the directions in which the action participants are now engaged, namely: copy synchronization in disconnected computing, mobile transactions, database embedded in ultra-light devices, data confidentiality, P2P dissemination models and middleware adaptability

Mobilité et bases de données : Etat de l'art et perspectives: 1ère partie. Action spécifique CNRS « Mobilité/Accès aux données »

National audienceThis paper is the result of the collective work done within the CNRS specific action Mobility/Data access with seven french laboratories IMAG-LSR, INT-Evry, LIP6, LORIA, PRiSM, EPFL, LIRMM . All pursuiving research in mobile computing and mobile databases. The action started in October 2001 for an initial period of one year. The activities and results of this action are available online at [AS_BDMobile]. The objective of this paper is to review the state of progress in mobile databases and identify major research directions. However, the research domain is so broad that we cannot pretend to be exhaustive. First, we propose a classification of mobile applications and a characterization of their execution environments. Then, we analyze the following issues: management of localization data, data access models, copy consistency and synchronization, management of embedded data, data confidentiality, and adaptability of software infrastructures to mobility and disconnection. For editorial reasons, this paper is published as a chronicle with two parts of equal importance.Ce document est le résultat d'un travail collectif réalisé par les membres de l'action spécifique CNRS « Mobilité/Accès aux données ». Il fait le point sur l'état d'avancement des travaux réalisés dans le domaine des bases de données mobiles et identifie quelques orientations de recherche jugées particulièrement pertinentes. Compte tenu de la largeur du domaine, ce document ne prétend cependant pas à l'exhaustivité. Après une classification des applications mobiles et une caractérisation de leur environnement d'exécution, les problématiques suivantes sont analysées : gestion des données de localisation, modèles d'accès aux données, cohérence des traitements et synchronisation de copies, gestion de données embarquées, confidentialité des données et enfin adaptabilité des infrastructures logicielles à la mobilité et à la déconnexion

Database Versions to Represent Bitemporal Databases

. We present a new approach to implement an object bitemporal database where both valid-time and transaction-time are represented. It is based on the DataBase Version model, which allows an efficient management of object versions. This facilitates the manipulation of past events and allows a straightforward representation of branching evolution in valid-time. Keywords : bitemporal database, valid-time, transaction time, versions. Introduction In many applications time must be considered and introduced as an information stored in the database, as it has been pointed out in a huge literature (see for instance [Cen]). Among the various temporal dimensions that have been studied in databases, two of them appear particularly important, useful and moreover complementary: the valid-time of a fact which expresses the time when this fact is true in the real world, and the transaction-time which is the time of storing the fact in the database. They gave birth to bitemporal data models, s..

Web page segmentation evaluation

International audienceIn this paper, we present a framework for evaluating segmentation algorithms for Web pages. Web page segmentation consists in dividing a Web page into coherent fragments, called blocks. Each block represents one distinct information element in the page. We define an evaluation model that includes different metrics to evaluate the quality of a segmentation obtained with a given algorithm. Those metrics compute the distance between the obtained segmentation and a manually built segmentation that serves as a ground truth. We apply our framework to four state-of-the-art segmentation algorithms (BOM, Block Fusion, VIPS and JVIPS) on several categories (types) of Web pages. Results show that the tested algorithms usually perform rather well for text extraction, but may have serious problems for the extraction of geometry. They also show that the relative quality of a segmentation algorithm depends on the category of the segmented page

Freshness Control of XML Documents for Query Load Balancing

International audienceWe present an approach for controlling the freshness of replicated XML documents. The main idea is that read-only transactions may accept to read stale data, provided they can express an upper bound on the staleness of the data they read. Controlling the freshness of data accessed by read-only transactions greatly improves load balancing since it allows for choosing a node for executing the transaction even if it is not perfectly fresh. Such a routing is based on detecting which parts of a document are likely to be updated by a given transaction. Due to the rich nature of XML, the problem is quite more complex than for relational SQL data. We present a new algorithm for conflict detection between transactions, needed to estimate freshness of data according to the missing transactions on a node. We also present new freshness measures, in order to take into account the structure/content nature of XML

Block-based Migration from HTML4 Standard to HTML5 Standard in the Context of Web Archives

International audienceWeb archives are not exempt of format obsolescence. In the near future Web pages written in HTML4 format, could be obsolete. We will have to choose between two preservation strategies: emulation or migration. The first option is the most evident, however due to the size of the Web and the amount of information that Web archives handle it is not practical. In the other hand migration to HTML5 format seems plausible. This is a challenge because we need to modify a page (in HTML4 format) and include elements that not even exists in this format (as the HTML5 semantic elements). Using the Web page segmentation we show that, with the appropriate granularity, blocks look alike these semantic elements. We present the use our segmentation tool, BoM (Block-o-Matic), for helping achieve the migration of Web pages from HTML4 format to HTML5 format in the context of Web archives. We also present an evaluation framework for Web page segmentation, that helps to produce metrics needed to compare the original and migrated version. If both versions are similar the migration has been successful. We show the experiments and results obtained on a sample of 40 pages. We made the manual segmentations for each page using our MoB tool. Results shows that in the migration process there is no data loss but in the migrated version (after adding the semantic elements) the margin is changed. This is, it adds whitespace that change the elements position, shifting elements slightly on the page. While this is imperceptible to the human eye, for systems it is difficult to handle without previous knowledge of this situation