A ictiofauna da ria de Aveiro: estrutura, dinâmica e populações

O objectivo global deste trabalho consistiu em estudar aspectos da estrutura e dinâmica da ictiofauna da Ria de Aveiro, sistema lagunar estuarino com 43 km2 de extensão, em baixa-mar, que sofre influências dulçaquícolas e marinhas e fica situado entre 40º 30’-40º52’N and 8º35’-8º47W no litoral da costa Portuguesa. A ictiofauna foi capturada mensalmente, de Dezembro de 1996 a Novembro de 1997, em nove estações de amostragem dispersas pela laguna, com uma rede de pesca tradicional “chincha”. Foram também registados os seguintes parâmetros abióticos hidrológicos: temperatura, salinidade, oxigénio dissolvido e transparência. A temperatura variou entre 6,5 e 27,6ºC, a salinidade entre 0 e 41‰, o oxigénio dissolvido entre 1,2 e 11,4 mg.l-1 e a transparência entre 7,3 e 100,0%. A variação da salinidade e a transparência da água entre as estações de amostragem, assim como a variação da temperatura, salinidade e oxigénio dissolvido, ao longo dos meses, foram significativas. Foram capturados 14.598 exemplares pertencentes a 43 espécies de 21 famílias de Teleósteos. O número de espécies e densidade da ictiofauna foram mais elevados no Verão e nas estações mais perto da entrada da laguna, em especial na Barra e na Torreira, enquanto que a biomassa sofreu oscilações consideráveis ao longo dos meses e mostrou-se mais elevada nas estações mais afastadas da embocadura. As espécies marinhas sazonais foram as mais numerosas e registaram a maior biomassa e as categorias “marinha juvenil” e “estuarina residente” registaram o maior número de espécies. Mugilidae, Atherinidae e Clupeidae foram as famílias mais abundantes. Seis espécies representaram cerca de 74% da densidade total e cerca de 63% da biomassa total e ocorreram em todas as estações e em todos os meses. Pode-se concluir que a Ria de Aveiro, com elevada variação espacial e sazonal nos parâmetros abióticos, apresenta uma comunidade de peixes rica e representativa, comparada com lagunas costeiras estuarinas Europeias.

DACA: architecture to implement dynamic access control mechanisms on business tier components

Access control is a software engineering challenge in database applications. Currently, there is no satisfactory solution to dynamically implement evolving fine-grained access control mechanisms (FGACM) on business tiers of relational database applications. To tackle this access control gap, we propose an architecture, herein referred to as Dynamic Access Control Architecture (DACA). DACA allows FGACM to be dynamically built and updated at runtime in accordance with the established fine-grained access control policies (FGACP). DACA explores and makes use of Call Level Interfaces (CLI) features to implement FGACM on business tiers. Among the features, we emphasize their performance and their multiple access modes to data residing on relational databases. The different access modes of CLI are wrapped by typed objects driven by FGACM, which are built and updated at runtime. Programmers prescind of traditional access modes of CLI and start using the ones dynamically implemented and updated. DACA comprises three main components: Policy Server (repository of metadata for FGACM), Dynamic Access Control Component (DACC) (business tier component responsible for implementing FGACM) and Policy Manager (broker between DACC and Policy Server). Unlike current approaches, DACA is not dependent on any particular access control model or on any access control policy, this way promoting its applicability to a wide range of different situations. In order to validate DACA, a solution based on Java, Java Database Connectivity (JDBC) and SQL Server was devised and implemented. Two evaluations were carried out. The first one evaluates DACA capability to implement and update FGACM dynamically, at runtime, and, the second one assesses DACA performance against a standard use of JDBC without any FGACM. The collected results show that DACA is an effective approach for implementing evolving FGACM on business tiers based on Call Level Interfaces, in this case JDBC.

Model of access to natural language sources in electronic government

For the actual existence of e-government it is necessary and crucial to provide public information and documentation, making its access simple to citizens. A portion, not necessarily small, of these documents is in an unstructured form and in natural language, and consequently outside of which the current search systems are generally able to cope and effectively handle. Thus, in thesis, it is possible to improve access to these contents using systems that process natural language and create structured information, particularly if supported in semantics. In order to put this thesis to test, this work was developed in three major phases: (1) design of a conceptual model integrating the creation of structured information and making it available to various actors, in line with the vision of e-government 2.0; (2) definition and development of a prototype instantiating the key modules of this conceptual model, including ontology based information extraction supported by examples of relevant information, knowledge management and access based on natural language; (3) assessment of the usability and acceptability of querying information as made possible by the prototype - and in consequence of the conceptual model - by users in a realistic scenario, that included comparison with existing forms of access. In addition to this evaluation, at another level more related to technology assessment and not to the model, evaluations were made on the performance of the subsystem responsible for information extraction. The evaluation results show that the proposed model was perceived as more effective and useful than the alternatives. Associated with the performance of the prototype to extract information from documents, comparable to the state of the art, results demonstrate the feasibility and advantages, with current technology, of using natural language processing and integration of semantic information to improve access to unstructured contents in natural language. The conceptual model and the prototype demonstrator intend to contribute to the future existence of more sophisticated search systems that are also more suitable for e-government. To have transparency in governance, active citizenship, greater agility in the interaction with the public administration, among others, it is necessary that citizens and businesses have quick and easy access to official information, even if it was originally created in natural language.