Implementação de um sistema temporal em um banco de dados orientado a objetos

Orientador: Claudia Bauzer MedeirosDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Ciencia da ComputaçãoResumo: Vários modelos têm sido propostos para incorporar o conceito de Tempo em Banco de Dados. A maioria destes modelos limita-se a incorporar as facilidades temporais em Sis­temas de Bancos de Dados Relacionais. Contudo, a maioria das aplicações que requerem um gerenciamento temporal de dados apresenta uma natureza orientada a objeto. As pesquisas sobre a incorporação de Tempo em Bancos de Dados Orientado a Objetos ainda estão em uma fase inicial. Este trabalho apresenta mais uma contribuição para o desenvolvimento das pesquisas nesta área. A contribuição consiste na implementação de um sistema de gerenciamento de tempo para um banco de dados orientados a objetos. Este sistema, a Camada de Gerenciamento Temporal, foi implementado sobre o sistema O2 e permite a definição e gerenciamento de dados temporais orientado a objetos, bem como o processamento de consultas temporais.Abstract: Many temporal data models have been suggested. A great number of these models is based on incorporating time only for relational databases systems. However, the applications that require temporal data management presents a object-oriented nature. Research on object-oriented database systems is still in its initial phase. This work presents a practical contribution to the research in this area. This contribution consists in the development of a temporal data management system for an object oriented database. This system - The Temporal Management Layer - was built on top of the O2 database system and allows the definition and management of object oriented temporal data, as well as the processing of temporal queries.MestradoMestre em Ciência da Computaçã

Operadores de junção baseados em mecanismos de hash para o processamento de consultas em bancos de dados.

Join algorithms constitute a key element for processing queries on databases. In this paper, the evolution of hash-based join algorithms is investigated. Conventional algorithms such as Simple Hash Join, Grace Hash Join and Hybrid Hash Join which were designed for conventional databases architectures are described and analyzed. Furthermore, algorithms such as Symmetric Hash Join, MobiJoin, Hash-Merge Join and MJoin for implementing the join operator in environments with more complex query processing requirements (e.g. mobile computing environment) are presented and analyzed as well.Os algoritmos de junção constituem um elemento chave para o desempenho do processamento de consultas. Com a evolução dos ambientes de execução de consultas tornou-se necessária o desenvolvimento de algoritmos mais eficientes para implementar o operador de junção. Neste trabalho é realizado um estudo sobre a evolução dos algoritmos de junção baseados na técnica de hashing. Serão analisadas estratégias convencionais como o Simple Hash Join, o Grace Hash Join e o Hybrid Hash Join, projetadas para arquiteturas de bancos de dados convencionais, até aquelas capazes de oferecer suporte a ambientes com processamentos de consultas mais complexos, como os de computação móvel. Os algoritmos hash capazes de atender a algumas das necessidades destes novos ambientes incluem o Symmetric Hash Join, o MobiJoin, o Hash-Merge Join e o MJoin

Ontology-based question answering systems over knowledge bases: a survey

Searching relevant, specific information in big data volumes is quite a challenging task. Despite the numerous strategies in the literature to tackle this problem, this task is usually carried out by resorting to a Question Answering (QA) systems. There are many ways to build a QA system, such as heuristic approaches, machine learning, and ontologies. Recent research focused their efforts on ontology-based methods since the resulting QA systems can benefit from knowledge modeling. In this paper, we present a systematic literature survey on ontology-based QA systems regarding any questions. We also detail the evaluation process carried out in these systems and discuss how each approach differs from the others in terms of the challenges faced and strategies employed. Finally, we present the most prominent research issues still open in the field

Abstract

A multidatabase consists of a collection of autonomous local databases. Systems used to manage multidatabases are called multidatabase systems (MDBSs). In such a system, global transactions are executed under the control of the MDBS. Independently, local transactions are submitted directly to a local DBS (LDBS) by local applications. An MDBS should provide a mechanism to globally manage transactions. However, global transactions are long-living and involve operations on multiple and autonomous local databases. Moreover, MDBSs do not have any information about the existence and execution order of local transactions. Thus, conventional approaches to manage transactions are unsuitable for MDBSs. In this paper, we address the reliability problem in MDBSs. For this purpose, we propose two types of protocols for making MDBSs resilient to failures. One type of protocol should enforce that, when a given global transaction completes its execution, it has the same state (committed or aborted) at every site it has run. The other type determines the actions to be triggered after failures in a multidatabase environment. These protocols can reduce the frequency of global transaction undo after the occurrence of failures, and make the MDBS able to deal with failures which may occur in a multidatabase environment.

On the effect of human mobility to the design of metropolitan mobile opportunistic networks of sensors

We live in a world where demand for monitoring natural and artificial phenomena is growing. The practical importance of Sensor Networks is continuously increasing in our society due to their broad applicability to tasks such as traffic and air-pollution monitoring, forest-fire detection, agriculture, and battlefield communication. Furthermore, we have seen the emergence of sensor technology being integrated in everyday objects such as cars, traffic lights, bicycles, phones, and even being attached to living beings such as dolphins, trees, and humans. The consequence of this widespread use of sensors is that new sensor network infrastructures may be built out of static (e.g., traffic lights) and mobile nodes (e.g., mobile phones, cars). The use of smart devices carried by people in sensor network infrastructures creates a new paradigm we refer to as Social Networks of Sensors (SNoS). This kind of opportunistic network may be fruitful and economically advantageous where the connectivity, the performance, of the scalability provided by cellular networks fail to provide an adequate quality of service. This paper delves into the issue of understanding the impact of human mobility patterns to the performance of sensor network infrastructures with respect to four different metrics, namely: detection time, report time, data delivery rate, and network coverage area ratio. Moreover, we evaluate the impact of several other mobility patterns (in addition to human mobility) to the performance of these sensor networks on the four metrics above. Finally, we propose possible improvements to the design of sensor network infrastructures

Operadores de junção baseados em mecanismos de hash para o processamento de consultas em bancos de dados.

Join algorithms constitute a key element for processing queries on databases. In this paper, the evolution of hash-based join algorithms is investigated. Conventional algorithms such as Simple Hash Join, Grace Hash Join and Hybrid Hash Join which were designed for conventional databases architectures are described and analyzed. Furthermore, algorithms such as Symmetric Hash Join, MobiJoin, Hash-Merge Join and MJoin for implementing the join operator in environments with more complex query processing requirements (e.g. mobile computing environment) are presented and analyzed as well.Os algoritmos de junção constituem um elemento chave para o desempenho do processamento de consultas. Com a evolução dos ambientes de execução de consultas tornou-se necessária o desenvolvimento de algoritmos mais eficientes para implementar o operador de junção. Neste trabalho é realizado um estudo sobre a evolução dos algoritmos de junção baseados na técnica de hashing. Serão analisadas estratégias convencionais como o Simple Hash Join, o Grace Hash Join e o Hybrid Hash Join, projetadas para arquiteturas de bancos de dados convencionais, até aquelas capazes de oferecer suporte a ambientes com processamentos de consultas mais complexos, como os de computação móvel. Os algoritmos hash capazes de atender a algumas das necessidades destes novos ambientes incluem o Symmetric Hash Join, o MobiJoin, o Hash-Merge Join e o MJoin

XVII Simpósio Brasileiro de Banco de Dados AMDB: An Approach for Sharing Mobile Databases in Dynamically Configurable Environments

We define a Mobile Database Community (MDBC) as a dynamic collection of autonomous mobile databases in which each database user can access databases in the community through a wireless communication infrastructure. New participants may join to an MDBC as they move within communication range of one or more hosts which are members of the MDBC. On other hand, MDBC participants may transiently disconnect from the network due to communication disruptions or to save power. For that reason, an MDBC can be characterized as a dynamically configurable environment. This paper describes an agent-based architecture, called AMDB (Accessing Mobile Databases), which enables such communities to be formed opportunistically over mobile database hosts in ad hoc configurable environments. The AMDB architecture is fully distributed and exploits physical mobility of hosts and logical mobility of database queries and their results across mobile hosts. A prototype of the proposed architecture is currently being developed based on the IBM agent system, called AGLETS. 1