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The fields of application of spatio-temporal systems, i.e., systems that must operate with time-varying spatial properties, are vast and heterogeneous. Since it would be difficult to treat such diversity as a whole, we introduce a classification for spatio-temporal systems based on the properties of the represented objects. Building on this classification, we also claim that features of some complex objects can be derived from those of simpler ones, suggesting an evolutionary approach, starting with the study of simple objects and progressing by enriching them with new features. This paper focuses on the definition of a data model for representation of moving points. The model is based on the decomposition of the trajectory of moving points into sections. The movement within each section of a trajectory is described by a variability function. Since, for most systems, it is not possible to store the exact knowledge about the movement of a mobile, the answers to queries may be imprecise. We propose two additional approaches to deal with imprecision, the superset and the subset semantics, based on a maximum value for the variability function, and a smooth technique to integrate them in the model. Finally, we analyse some functional aspects of the implementation of the data model on a Relational Database Management System (RDBMS) and outline some directions for future research.

Geographical Information Systems were originally intended to deal with snapshots representing a single state of some reality but there axe more and more applications requiring the representation and querying of time-varying information. This work addresses the representation of moving objects on GIS.The continuous nature of movement raises problems for representation in information systems due to the limited capacity of storage systems and the inherently discrete nature of measurement instruments. The stored information has therefore to be partial and does not allow an exact inference of the real-world object's behavior. To cope with this, query operations must take uncertainty into consideration in their semantics in order to give accurate answers to the users.The paper proposes a set of operations to be included in a GIS or a spatial database to make it able to answer queries on the spatio-temporal behavior of moving objects. The operations have been selected according to the requirements of real applications and their semantics with respect to uncertainty is specified. A collection of examples from a case study is included to illustrate the expressiveness of the proposed operations.

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This paper deals with the application of satellite images to characterize some aspects of the circulation dynamics of the Tinto-Odiel estuary using turbidity patterns as ‘natural tracers’. 15 images (Landsat TM and Spot HRV) were processed to provide synoptic, instantaneous views of the circulation patterns under different environmental conditions. In addition, a comparison was made between results of oceanographic field work, using biplanes and fluorescent tracers, and satellite image turbidity patterns used as ‘ground truth’ data for specific hydroclimatic situations. This approach allowed (1) the identification and mapping of dynamic processes of interest during a theoretical tidal cycle, (2) the elaboration of additional information on the ‘flow schemes’ at the mouth of the estuary with improved spatial and temporal resolution, and (3) the supply of basic data to improve the knowledge of exchange processes between estuarine and coastal waters. The results of this study are considered to be useful for the management of the estuarine system

This paper deals with the design and implementation of a data model and operations for dealing with continuously changing spatial data in Oracle 11g object-relational DBMS. The data model relies on abstract data types but we introduce modifications to the internal structure of the spatiotemporal data representations proposed in the literature, to reduce storage requirements and to enable the reuse of data during the execution of queries. We show how to implement spatiotemporal operations relying on the spatial functions released by the underlying DBMS and how to use the alternative data representations to reduce the volume of temporary data created in the evaluation of spatiotemporal operations. We also demonstrate how to use the proposed data types and operations for storage and manipulation of moving objects data using SQL. Finally, we discuss on the advantages and disadvantages of the proposed solutions.

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O termo governance adquiriu, desde os anos 90 do século XX, particular destaque na discussão teórica e na investigação empírica das ciências sociais. O presente artigo visa o esclarecimento do conceito de governance (governação/governança) e, principalmente, perceber as implicações da lógica da governance nas políticas públicas de turismo: enquadrando-a no movimento de reforma do setor público. De seguida, procede-se à identificação do “estado da arte” sobre a governance no turismo – através da análise de um conjunto de artigos selecionados da base de dados Scopus –, para compreender como nesse âmbito se entende o conceito e de que modo a lógica da governance alterou o papel do Estado nas políticas públicas de turismo. Os resultados deste estudo permitem verificar que a distinção entre governação e governança ajuda a melhor compreender os diferentes modos de atuação do Estado, em especial no que concerne às políticas públicas de turismo.