Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 60-61). Also available in electronic version.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 77-84). Also available in electronic version.

Thesis (M.Sc.)--York University, 2004. Graduate Programme in Computer Science. / Typescript. Includes bibliographical references (leaves 112-116). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: LINK NOT YET AVAILABLE.

Thesis (M.S.)--Rochester Institute of Technology, 2007. / Typescript. Includes bibliographical references (leaves 47-48).

Thesis (M.S.) -- Worcester Polytechnic Institute. / Keywords: Continuous query processing; Adaptation policies; Partitioned window join operator. Includes bibliographical references (p.).

abstract: The Resource Description Framework (RDF) is a specification that aims to support the conceptual modeling of metadata or information about resources in the form of a directed graph composed of triples of knowledge (facts). RDF also provides mechanisms to encode meta-information (such as source, trust, and certainty) about facts already existing in a knowledge base through a process called reification. In this thesis, an extension to the current RDF specification is proposed in order to enhance RDF triples with an application specific weight (cost). Unlike reification, this extension treats these additional weights as first class knowledge attributes in the RDF model, which can be leveraged by the underlying query engine. Additionally, current RDF query languages, such as SPARQL, have a limited expressive power which limits the capabilities of applications that use them. Plus, even in the presence of language extensions, current RDF stores could not provide methods and tools to process extended queries in an efficient and effective way. To overcome these limitations, a set of novel primitives for the SPARQL language is proposed to express Top-k queries using traditional query patterns as well as novel predicates inspired by those from the XPath language. Plus, an extended query processor engine is developed to support efficient ranked path search, join, and indexing. In addition, several query optimization strategies are proposed, which employ heuristics, advanced indexing tools, and two graph metrics: proximity and sub-result inter-arrival time. These strategies aim to find join orders that reduce the total query execution time while avoiding worst-case pattern combinations. Finally, extensive experimental evaluation shows that using these two metrics in query optimization has a significant impact on the performance and efficiency of Top-k queries. Further experiments also show that proximity and inter-arrival have an even greater, although sometimes undesirable, impact when combined through aggregation functions. Based on these results, a hybrid algorithm is proposed which acknowledges that proximity is more important than inter-arrival time, due to its more complete nature, and performs a fine-grained combination of both metrics by analyzing the differences between their individual scores and performing the aggregation only if these differences are negligible. / Dissertation/Thesis / M.S. Computer Science 2010

abstract: Most existing approaches to complex event processing over streaming data rely on the assumption that the matches to the queries are rare and that the goal of the system is to identify these few matches within the incoming deluge of data. In many applications, such as stock market analysis and user credit card purchase pattern monitoring, however the matches to the user queries are in fact plentiful and the system has to efficiently sift through these many matches to locate only the few most preferable matches. In this work, we propose a complex pattern ranking (CPR) framework for specifying top-k pattern queries over streaming data, present new algorithms to support top-k pattern queries in data streaming environments, and verify the effectiveness and efficiency of the proposed algorithms. The developed algorithms identify top-k matching results satisfying both patterns as well as additional criteria. To support real-time processing of the data streams, instead of computing top-k results from scratch for each time window, we maintain top-k results dynamically as new events come and old ones expire. We also develop new top-k join execution strategies that are able to adapt to the changing situations (e.g., sorted and random access costs, join rates) without having to assume a priori presence of data statistics. Experiments show significant improvements over existing approaches. / Dissertation/Thesis / M.S. Computer Science 2011

A fim de consultar uma mesma informação em fontes XML heterogêneas seria desejável poder formular uma única consulta em relação a um esquema global conceitual e então traduzi-la automaticamente para consultas XML para cada uma das fontes. CXPath (Conceptual XPath) é uma proposta de linguagem para consultar fontes XML em um nível conceitual. Essa linguagem foi desenvolvida para simplificar o processo de tradução de consultas em nível conceitual para consultas em nível XML. Ao mesmo tempo, a linguagem tem como objetivo a facilidade de aprendizado de sua sintaxe. Por essa razão, sua sintaxe é bastante semelhante à da linguagem XPath utilizada para consultar documentos XML. Nesta dissertação é definido formalmente o mecanismo de tradução de consultas em nível conceitual, escritas em CXPath, para consultas em nível XML, escritas em XPath. É mostrado o tratamento do relacionamento de herança no mecanismo de tradução, e é feita uma discussão sobre a relação entre a expressividade do modelo conceitual e o mecanismo de tradução. Existem situações em que a simples tradução de uma consulta CXPath não contempla alguns resultados, pois as fontes de dados podem ser incompletas. Neste trabalho, o modelo conceitual que constitui o esquema global do sistema de integração de dados é estendido com dependências de inclusão e o mecanismo de resolução de consultas é modificado para lidar com esse tipo de dependência. Mais especificamente, são apresentados mecanismos de reescrita e eliminação de redundâncias de consultas a fim de lidar com essas dependências. Com o aumento de expressividade do esquema global é possível inferir resultados, a partir dos dados disponíveis no sistema de integração, que antes não seriam contemplados com a simples tradução de uma consulta. Também é apresentada a abordagem para integração de dados utilizada nesta dissertação de acordo com o arcabouço formal para integração de dados proposto por (LENZERINI, 2002). De acordo com o autor, tal arcabouço é geral o bastante para capturar todas as abordagens para integração de dados da literatura, o que inclui a abordagem aqui mostrada. / In order to search for the same information in heterogeneous XML data sources, it would be desirable to state a single query against a global conceptual schema and then translate it automatically into an XML query for each specific data source. CXPath (for Conceptual XPath ) has been proposed as a language for querying XML sources at the conceptual level. This language was developed to simplify the translation process of queries at conceptual level to queries at XML level. At the same time, one of the goals of the language design is to facilitate the learning of its syntax. For this reason its syntax is similar to the XPath language used for querying XML documents. In this dissertation, a translation mechanism of queries at conceptual level, written in CXPath, to queries at XML level, written in XPath, is formally defined. The inheritance relationship in the translation mechanism is shown, being discussed the relation between the conceptual model expressivity and the translation mechanism. In some cases, the translation of a CXPath query does not return some of the answers because the data sources may be incomplete. In this work, the conceptual model, which is the basis for the data integration system’s global schema, is improved with inclusion dependencies, and the query answering mechanism is modified to deal with this kind of dependency. More specifically, mechanisms of query rewriting and redundancy elimination are presented to deal with this kind of dependency. This global schema improvement allows infer results, with the data available in the system, that would not be provided with a simple query translation. The approach of data integration used in this dissertation is also presented within the formal framework for data integration proposed by (LENZERINI, 2002). According to the author, that framework is general enough to capture all approaches in the literature, including, in particular, the approach considered in this dissertation.

Answering conjunctive queries over ontology-enriched datasets is a core reasoning task for many applications of semantic technologies. Conjunctive query answering is, however, computationally very expensive, which has led to the development of query answering procedures that sacrifice either the expressive power of ontology languages, or the completeness of query answers in order to improve scalability. This thesis describes a hybrid approach to query answering over OWL 2 ontologies that combines a datalog reasoner with a fully-fledged OWL 2 reasoner in order to provide scalable "pay-as-you-go" performance. The key feature of this hybrid approach is that it delegates the bulk of the computation to the datalog reasoner and resorts to expensive OWL 2 reasoning only as necessary to fully answer the query. Although the main goal of this thesis is to efficiently answer queries over OWL 2 ontologies, the technical results are more general and the approach is applicable to first-order knowledge representation languages that can be captured by rules allowing for existential quantification and disjunction in the head; the only assumption is the availability of a datalog reasoner and a fully-fledged reasoner for the language of interest, both of which are used as "black boxes". All techniques proposed in this thesis are implemented in the PAGOdA system, which combines the datalog reasoner RDFox and the OWL 2 reasoner HermiT. An extensive evaluation shows that PAGOdA succeeds in providing scalable pay-as-you-go query answering for a wide range of OWL 2 ontologies, datasets and queries.

A fim de consultar uma mesma informação em fontes XML heterogêneas seria desejável poder formular uma única consulta em relação a um esquema global conceitual e então traduzi-la automaticamente para consultas XML para cada uma das fontes. CXPath (Conceptual XPath) é uma proposta de linguagem para consultar fontes XML em um nível conceitual. Essa linguagem foi desenvolvida para simplificar o processo de tradução de consultas em nível conceitual para consultas em nível XML. Ao mesmo tempo, a linguagem tem como objetivo a facilidade de aprendizado de sua sintaxe. Por essa razão, sua sintaxe é bastante semelhante à da linguagem XPath utilizada para consultar documentos XML. Nesta dissertação é definido formalmente o mecanismo de tradução de consultas em nível conceitual, escritas em CXPath, para consultas em nível XML, escritas em XPath. É mostrado o tratamento do relacionamento de herança no mecanismo de tradução, e é feita uma discussão sobre a relação entre a expressividade do modelo conceitual e o mecanismo de tradução. Existem situações em que a simples tradução de uma consulta CXPath não contempla alguns resultados, pois as fontes de dados podem ser incompletas. Neste trabalho, o modelo conceitual que constitui o esquema global do sistema de integração de dados é estendido com dependências de inclusão e o mecanismo de resolução de consultas é modificado para lidar com esse tipo de dependência. Mais especificamente, são apresentados mecanismos de reescrita e eliminação de redundâncias de consultas a fim de lidar com essas dependências. Com o aumento de expressividade do esquema global é possível inferir resultados, a partir dos dados disponíveis no sistema de integração, que antes não seriam contemplados com a simples tradução de uma consulta. Também é apresentada a abordagem para integração de dados utilizada nesta dissertação de acordo com o arcabouço formal para integração de dados proposto por (LENZERINI, 2002). De acordo com o autor, tal arcabouço é geral o bastante para capturar todas as abordagens para integração de dados da literatura, o que inclui a abordagem aqui mostrada. / In order to search for the same information in heterogeneous XML data sources, it would be desirable to state a single query against a global conceptual schema and then translate it automatically into an XML query for each specific data source. CXPath (for Conceptual XPath ) has been proposed as a language for querying XML sources at the conceptual level. This language was developed to simplify the translation process of queries at conceptual level to queries at XML level. At the same time, one of the goals of the language design is to facilitate the learning of its syntax. For this reason its syntax is similar to the XPath language used for querying XML documents. In this dissertation, a translation mechanism of queries at conceptual level, written in CXPath, to queries at XML level, written in XPath, is formally defined. The inheritance relationship in the translation mechanism is shown, being discussed the relation between the conceptual model expressivity and the translation mechanism. In some cases, the translation of a CXPath query does not return some of the answers because the data sources may be incomplete. In this work, the conceptual model, which is the basis for the data integration system’s global schema, is improved with inclusion dependencies, and the query answering mechanism is modified to deal with this kind of dependency. More specifically, mechanisms of query rewriting and redundancy elimination are presented to deal with this kind of dependency. This global schema improvement allows infer results, with the data available in the system, that would not be provided with a simple query translation. The approach of data integration used in this dissertation is also presented within the formal framework for data integration proposed by (LENZERINI, 2002). According to the author, that framework is general enough to capture all approaches in the literature, including, in particular, the approach considered in this dissertation.