A platform to support object database research

Databases play a key role in an increasingly diverse range of applications and settings. New requirements are continually emerging and may differ substantially from one domain to another, sometimes even to the point of conflict. To address these challenges, database systems are evolving to cater for new application domains. Yet little attention has been given to the process of researching and developing database concepts in response to new requirements. We present a platform designed to support database research in terms of experimentation with different aspects of database systems ranging from the data model to the distribution architecture. Our platform is based on the notion of metamodel extension modules, inspired by proposals for adaptive and configurable database management systems. However, rather than building a tailored system from existing components, we focus on the process of designing new components. To qualitatively evaluate our platform, we present a series of case studies where our approach was used successfully to experiment with concepts designed to support a variety of novel application domains

Functional Ontologies and Their Application to Hydrologic Modeling: Development of an Integrated Semantic and Procedural Knowledge Model and Reasoning Engine

This dissertation represents the research and development of new concepts and techniques for modeling the knowledge about the many concepts we as hydrologists must understand such that we can execute models that operate in terms of conceptual abstractions and have those abstractions translate to the data, tools, and models we use every day. This hydrologic knowledge includes conceptual (i.e. semantic) knowledge, such as the hydrologic cycle concepts and relationships, as well as functional (i.e. procedural) knowledge, such as how to compute the area of a watershed polygon, average basin slope or topographic wetness index. This dissertation is presented as three papers and a reference manual for the software created. Because hydrologic knowledge includes both semantic aspects as well as procedural aspects, we have developed, in the first paper, a new form of reasoning engine and knowledge base that extends the general-purpose analysis and problem-solving capability of reasoning engines by incorporating procedural knowledge, represented as computer source code, into the knowledge base. The reasoning engine is able to compile the code and then, if need be, execute the procedural code as part of a query. The potential advantage to this approach is that it simplifies the description of procedural knowledge in a form that can be readily utilized by the reasoning engine to answer a query. Further, since the form of representation of the procedural knowledge is source code, the procedural knowledge has the full capabilities of the underlying language. We use the term functional ontology to refer to the new semantic and procedural knowledge models. The first paper applies the new knowledge model to describing and analyzing polygons. The second and third papers address the application of the new functional ontology reasoning engine and knowledge model to hydrologic applications. The second paper models concepts and procedures, including running external software, related to watershed delineation. The third paper models a project scenario that includes integrating several models. A key advance demonstrated in this paper is the use of functional ontologies to apply metamodeling concepts in a manner that both abstracts and fully utilizes computational models and data sets as part of the project modeling process

Um estudo de performance de uma ferramenta de Object/Relational Mapping

Dissertação para obtenção do Grau de Mestre em Engenharia InformáticaAtualmente existem inúmeras ferramentas que ajudam no desenvolvimento de aplicações multi-camada, retirando aos programadores a responsabilidade de definir a estrutura e as interações com o sistema de gestão de base de dados que serve de repositório permanente para os dados. Porém, a introdução de mais uma camada entre a aplicação e a base de dados tem necessariamente implicações no desempenho global do sistema. Estes sistemas recorrem por isso a múltiplas estratégias para diminuir o overhead imposto pela sua utilização, incorporando múltiplas soluções de caching. O trabalho reportado nesta dissertação visa realizar um estudo para compreender a dimensão das perdas de performance introduzidas pela utilização de ferramentas de mapeamento objeto relacional numa arquitetura multi-camada e o impacto da utilização dos mecanismos de caching disponíveis nesses sistemas, tanto num contexto centralizado como num contexto distribuído. Para isso iremos medir a produtividade do benchmark TPC-W em duas variantes: uma (standard) que trabalha sobre uma base de dados relacional; e outra (adaptada) que trabalha sobre um sistema de mapeamento objeto-relacional, suportado também pela mesma de dados relacional. Nesta última variante também será testada a inclusão das várias caches suportadas pela ferramenta Object Relational Mapping(ORM) e avaliar os seus potenciais benefícios para o desempenho da aplicação. Da análise da produtividade das duas variantes do benchmark, pretende-se quantificar as perdas de desempenho decorrentes da introdução de mais uma camada entre a aplicação e a base de dados, bem como identificar a origem dessas perdas e potenciais formas de as mitigar.Fundação para a Ciência e Tecnologia - projecto de investigação Synergy-VM (PTDC/EIA-EIA/113613/2009

Analyzing user feedback of on-line communities

The economic success of the World Wide Web makes it a highly competitive environment for web businesses. For this reason, it is crucial for web business owners to learn what their customers want. This thesis provides a conceptual framework and an implementation of a system that helps to better understand the behavior and potential interests of web site visitors by accounting for both explicit and implicit feedback. This thesis is divided into two parts. The first part is rooted in computer science and information systems and uses graph theory and an extended click-stream analysis to define a framework and a system tool that is useful for analyzing web user behavior by calculating the interests of the users. The second part is rooted in behavioral economics, mathematics, and psychology and is investigating influencing factors on different types of web user choices. In detail, a model for the cognitive process of rating products on the Web is defined and an importance hierarchy of the influencing factors is discovered. Both parts make use of techniques from a variety of research fields and, therefore, contribute to the area of Web Science.Welche Interessen verfolgen meine Webseiten-Nutzer? Diese Frage beschäftigt viele Betreiber von Online-Unternehmen. Um in einem solch hart umkämpften Markt wie dem des Internetbusiness erfolgreich bestehen zu können, ist es für die Entscheidungsträger dieser Unternehmen ausschlaggebend zu verstehen, welche Ziele ihre Kunden verfolgen. Hauptziel der vorliegenden Arbeit ist es, diese Frage mit Hilfe eines konzeptionellen Bezugssystems und der Implementierung eines Systems zu beantworten. Beide Elemente berücksichtigen sowohl das Verhalten, als auch das explizite und das implizite Feedback der Webseiten-Nutzer. Der vorgeschlagene Lösungsansatz unterstützt Betreiber von Online-Unternehmen dabei ihre Kunden besser zu verstehen. Dies geschieht durch das Beobachten und Auswerten des Kundenverhaltens, um daraus die vermuteten Kundeninteressen zu berechnen. Außerdem werden, um den Prozess des Feedbackgebens besser zu verstehen, diejenigen Faktoren untersucht, die die Auswahl des Webseiten-Nutzers beim Feedbackgeben beeinflussen. Folgende Forschungsfragen werden in dieser Arbeit im Hinblick auf unterschiedliche Aspekte des Feedbacks von Webseiten-Nutzern untersucht: * Was lernen wir aus der Analyse des explizit und des implizit durch die Webseiten-Nutzer ausgeführten Feedbacks? * Was sind die wichtigsten Faktoren, die das Feedback von Webseiten-Nutzern beeinflussen

Efficient Reorganisation of Hybrid Index Structures Supporting Multimedia Search Criteria

This thesis describes the development and setup of hybrid index structures. They are access methods for retrieval techniques in hybrid data spaces which are formed by one or more relational or normalised columns in conjunction with one non-relational or non-normalised column. Examples for these hybrid data spaces are, among others, textual data combined with geographical ones or data from enterprise content management systems. However, all non-relational data types may be stored as well as image feature vectors or comparable types. Hybrid index structures are known to function efficiently regarding retrieval operations. Unfortunately, little information is available about reorganisation operations which insert or update the row tuples. The fundamental research is mainly executed in simulation based environments. This work is written ensuing from a previous thesis that implements hybrid access structures in realistic database surroundings. During this implementation it has become obvious that retrieval works efficiently. Yet, the restructuring approaches require too much effort to be set up, e.g., in web search engine environments where several thousands of documents are inserted or modified every day. These search engines rely on relational database systems as storage backends. Hence, the setup of these access methods for hybrid data spaces is required in real world database management systems. This thesis tries to apply a systematic approach for the optimisation of the rearrangement algorithms inside realistic scenarios. Thus, a measurement and evaluation scheme is created which is repeatedly deployed to an evolving state and a model of hybrid index structures in order to optimise the regrouping algorithms to make a setup of hybrid index structures in real world information systems possible. Thus, a set of input corpora is selected which is applied to the test suite as well as an evaluation scheme. To sum up, it can be said that this thesis describes input sets, a test suite including an evaluation scheme as well as optimisation iterations on reorganisation algorithms reflecting a theoretical model framework to provide efficient reorganisations of hybrid index structures supporting multimedia search criteria