ST4SQL: a spatio-temporal query language dealing with granularities

In many different application fields the amount and importance of spatio-temporal data (i.e., temporally and/or spatially qualified data) is increasing in last years and users need new solutions for their management. A framework for modeling spatio-temporal data in relational databases has been proposed in a previous work. The model is based on the notions of temporal, spatial, and spatio-temporal granularities. Once data have been modeled, they must be queried through query languages able to exploit also their spatio-temporal components. In this paper we propose a spatio-temporal query language, called ST4SQL. The proposed language extends the well-known SQL syntax and the T4SQL, a temporal query language proposed by Combi et al.. ST4SQL deals with different temporal, spatial, and spatio-temporal semantics with respect to temporal and spatial dimensions. These semantics allow one to specify how the system must manage spatio-temporal dimensions for evaluating the queries. Moreover, the query language introduces new constructs for grouping data with respect to temporal and spatial dimensions. Both semantics and grouping constructs take into account and exploit data qualified with spatio-temporal granularities.