A data model and query language for spatio-temporal decision support |
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Authors: | Leticia Gómez Bart Kuijpers Alejandro Vaisman |
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Affiliation: | 1.Instituto Tecnológico de Buenos Aires,Buenos Aires,Argentina;2.Hasselt University and Transnational University of Limburg,Diepenbeek,Belgium;3.Universidad de Buenos Aires,Buenos Aires,Argentina |
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Abstract: | In recent years, applications aimed at exploring and analyzing spatial data have emerged, powered by the increasing need of
software that integrates Geographic Information Systems (GIS) and On-Line Analytical Processing (OLAP). These applications
have been called SOLAP (Spatial OLAP). In previous work, the authors have introduced Piet, a system based on a formal data
model that integrates in a single framework GIS, OLAP (On-Line Analytical Processing), and Moving Object data. Real-world
problems are inherently spatio-temporal. Thus, in this paper we present a data model that extends Piet, allowing tracking
the history of spatial data in the GIS layers. We present a formal study of the two typical ways of introducing time into
Piet: timestamping the thematic layers in the GIS, and timestamping the spatial objects in each layer. We denote these strategies
snapshot-based and timestamp-based representations, respectively, following well-known terminology borrowed from temporal databases. We present and discuss
the formal model for both alternatives. Based on the timestamp-based representation, we introduce a formal First-Order spatio-temporal
query language, which we denote Lt,\mathcal{L}_t, able to express spatio-temporal queries over GIS, OLAP, and trajectory data. Finally, we discuss implementation issues, the
update operators that must be supported by the model, and sketch a temporal extension to Piet-QL, the SQL-like query language
that supports Piet. |
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