Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 124-138) Also available in print.

Mobility in distributed object systems is useful as it can provide such properties as load balancing, code to data movement, fault tolerance, migration to stable storage, and autonomous semantics. In a widely distributed system, these properties are important as they can help alleviate latency issues and increase performance within the system. Additionally, they provid more flexibility in the programming of distributed systems by relaxing static location restrictions. Location transparency removes the need for client objects to explicitly know or define the location of a server object when communicating. If a server object is capable of migration, relocation transparency maintains reference validity throughout the migration. Several models for providing relocation transparency exist, including the home location, forwarding location, and broadcast models. This thesis proposes a model that uses a distributed registry system and dynamic reference updating to provide location and relocation transparency. A registry system is used to provide location independence by resolving a location independent name to a reference that can be used by a client. A naming system is used to provide correct binding and production of names within the naming restrictions of the system. The thesis proposes that the choice of naming system within a distributed or mobile object system has a large effect on the system's ability to support efficient transparent object relocation. This thesis proposes that a formal analysis of naming systems enables the selection of an appropriate naming system for a distributed or mobile object system given the object system's naming, distribution and transparency requirements. This thesis presents a new classification scheme for naming systems, based on analysis of a broad spectrum of naming systems. A classification of existing mobile and distributed object systems with respect to existing naming models is provided. It is shown that the current models need to be refined and extended to completely and correctly classify the example systems. This thesis proposes extensions and refinements that enable correct and complete classification of mobile and distributed object systems with a need for transparency. The extended naming model is then used to describe a naming system that is capable of implementing any naming system classifiable by the extended model. A classification of a naming system to support the proposed model of location and relocation transparency is presented. A distributed ORB system is designed and implemented to support the distributed namespace and generic naming system implementation. The distributed ORB system is hierarchically structured and is capable of adapting in response to node failure. This ORB system is used to support client and server object integration in the DISCWorld metacomputing environment. The ORB system is used to provide migration, replication and cloning services to the DISCWorld metacomputing environment. A qualitative analysis of the generic naming system and the DISCWorld ORB system is performed. A comparison between the proposed model for location and relocation transparency and existing models is also presented. This comparison shows that the proposed model exhibits better location and relocation performance within the DISCWorld environment. The distributed nature of the ORB system and namespace provides a scalable nature in terms of namespace size, the number of objects within the system, and the frequency of location and relocation requests. / Thesis (Ph.D.)--Engineering (Department of Computer Science), 2000.

Thesis (doctorat)--Institut national agronomique Paris-Grignon, 1989. / Includes bibliographical references (p. 390-411).

Made available in DSpace on 2009-11-18T19:00:49Z (GMT). No. of bitstreams: 1 ACF21E.pdf: 2001646 bytes, checksum: f701f43c8d0badcc2458daf83fd88397 (MD5) Previous issue date: 2007 / Nowadays, the free software has been presented as an alternative to the acquisition structure of proprietors¿ software licenses, being adopted by a large number of companies. This study presents the analysis, through a case study, of a project of proprietors¿ software migration for free platforms. The main purpose was to identify decisive factors of success in the adoption of free softwares for private companies. For this, was used the single case methodology of study, presented by Yin (2005). The theoretical referential approaches issues related to the definitions and the historic of the free software, the resistance to information systems and the change resistance. The idea is to look for the fundamentals to support the researchers understanding of the situations observed in the field. The data found at this research was analyzed using a meta-frame, which has as the main point the Unified Theory of Acceptance and Use of Information Technology, developed by Venkatesh et al. (2003). Also, to complete this meta-frame, were used the Technology Acceptance Model, proposed by Davis (1989), and Interaction¿s Model of system and context of Use, developed by Markus (1983). The researche¿s result has been gotten by the analysis of documentation, interviews, questionnaires, direct observation and participant observation, that made possible the obtaining of valuable group of data on the researched subject. The result of this research allow the establishment of subsidies for the planning and development of project of proprietors¿ softwares migration for free softwares. / Atualmente, o software livre tem se apresentado como uma alternativa à estrutura de aquisição de licenças de softwares proprietários, sendo adotado por um número cada vez maior de empresas. O presente estudo apresenta a análise, através de um estudo de caso, de um projeto de migração de softwares proprietários para plataformas livres. Buscou-se identificar fatores determinantes de sucesso na adoção de softwares livres por empresas privadas. Para tal, foi utilizada a metodologia de estudo de caso único, apresentada por Yin (2005). O referencial teórico aborda questões relacionadas com as definições e o histórico dos softwares livres, resistência e sistemas de informação e resistência a mudanças, buscando levantar uma base teórica para auxiliar o pesquisador no entendimento dos fatores observados em campo. A pesquisa utilizou um meta-frame para análise dos dados levantados. Este meta-frame possui como ponto central o Modelo Unificado de Aceitação e Uso de Tecnologia da Informação, desenvolvido por Venkatesh et al. (2003). Completam este meta-frame o Modelo de Aceitação da Tecnologia, proposto por Davis (1989), e o Modelo da Interação Sistema Contexto de Uso, desenvolvido por Markus (1983). Os resultados da pesquisa foram obtidos através da análise de documentações, entrevistas, questionários, observações diretas e observações particulares, que possibilitaram a obtenção de um conjunto valioso de dados sobre o assunto pesquisado. As conclusões desta pesquisa permitem o estabelecimento de subsídios para o planejamento e desenvolvimento de um projeto de migração de softwares proprietários para softwares livres.

Web Systems are widely used and accepted due to their advantages over traditional desktop applications. Modernization of existing non-Web software towards the Web, however, is a complex and challenging task due to Legacy System characteristics. Independent Software Vendors are struggling to commence Web Migration because of the involved effort and risk. Through systematic field research and problem analysis, this situation is further analyzed, deriving a set of requirements that represent the effort and risk concerns and are used to assess the state of the art in the field. Existing Web Migration research exhibits gaps concerning dedicated approaches for the initial phase and feasibility of the proposed strategies with limited resources and expertise. This thesis proposes a solution to address the shortcomings above and support Independent Software Vendors to commence Web Migration, focusing on effort and risk. The main idea is to provide a set of dedicated solutions to close the identified gaps in the form of a methodology and a supporting toolsuite that transfer paradigms successfully solving similar problems in other areas of computer science into the Web Migration domain. These solutions constitute the proposed approach called Agile Web Migration for SMEs (AWSM), consisting of methods, tools, principles, and formalisms for reverse engineering, risk management, customer impact control, and migration strategy selection. The thesis describes the research on the devised ideas in the context of a collaboration project with an Independent Software Vendor. Applicability and feasibility of the concepts are demonstrated in several evaluation experiments, integrating empirical user studies and objective measurements. The thesis concludes with an evaluation based on requirements assessment and application of the solutions in the application scenario, and it provides an outlook towards future work.:1 Introduction 2 Requirements Analysis 3 State of the Art 4 Addressing Effort and Risk Concerns in Web Migration 5 AWSM Reverse Engineering Method 6 AWSM Risk Management Method 7 AWSM Customer Impact Control Method 8 Evaluation 9 Conclusion and Outlook / Web-basierte Software-Systeme werden weithin verwendet und akzeptiert aufgrund ihrer Vorteile gegenüber traditionellen Desktopanwendungen. Die Modernisierung von Nicht-Web-Software zu Web-Software stellt jedoch wegen der Charakteristika von Legacy-Systemen eine komplexe und herausfordernde Aufgabe dar. Unabhängigen Softwareproduzenten (Independent Software Vendors) fällt es schwer, Web Migration zu initiieren aufgrund des damit einhergehenden Aufwands und Risikos. Durch systematische Primärerhebungen und Problemanalyse wird diese Situation weitergehend untersucht und eine Reihe von Anforderungen abgeleitet, welche die Aufwands- und Riskobedenken repräsentieren und verwendet werden, um den Stand der Technik in diesem Gebiet zu bewerten. Existierende Web Migration Forschung weist Mängel hinsichtlich von dedizierten Ansätzen für die initiale Phase und der Machbarkeit der vorgeschlagenen Strategien mit begrenzten Ressourcen und begrenzter Expertise auf. Diese Dissertation schlägt eine Lösung für die oben ausgeführten Mängel vor, um unabhängige Softwareproduzenten bei der Initiierung einer Web Migration zu unterstützen, welche sich auf ihre Bedenken bezüglich des Aufwands und Risikos fokussiert. Die Grundidee ist es eine Sammlung von dedizierten Lösungen für die identifizierten Mängel in Form einer Methodologie und einer Reihe von unterstützenden Werkzeugen anzubieten, welche Paradigmen, die erfolgreich ähnliche Probleme in anderen Gebieten der Informatik lösen konnten, in die Web Migration Domäne transferieren. Diese Lösungen ergeben den vorgeschlagenen Ansatz, Agile Web Migration for SMEs (AWSM), welcher aus Methoden, Werkzeugen, Prinzipien und Formalismen für Reverse Engineering, Riskomanagement, Customer Impact Control und Migrationsstrategieauswahl bestehen. Die Dissertation beschreibt die Forschung an den im Rahmen einer Industriekooperation mit einem unabhängigen Softwareproduzenten entwickelten Ideen. Anwendbarkeit und Machbarkeit der Konzepte werden in mehreren Evaluationsexperimenten, welche empirische Nutzerstudien mit objektiven Messungen verbinden, demonstriert. Die Dissertation schließt mit einer bewertenden Evaluation basierend auf den Anforderungen und auf dem Einsatz der Lösungen im Anwendungsszenario, sowie einem Ausblick auf weiterführende Arbeiten.:1 Introduction 2 Requirements Analysis 3 State of the Art 4 Addressing Effort and Risk Concerns in Web Migration 5 AWSM Reverse Engineering Method 6 AWSM Risk Management Method 7 AWSM Customer Impact Control Method 8 Evaluation 9 Conclusion and Outlook