Pozzani and Combi proposed ST4SQL, an SQL-based query language extending SQL with new constructs for querying spatio-temporal data. In particular, ST4SQL deals with different temporal and spatial semantics, allowing one to specify how the system has to manage temporal and spatial dimensions for evaluating queries. Moreover, the query language introduces new constructs for grouping data with respect to temporal and spatial dimensions. All proposed constructs take into account data qualified with granularities. In this paper we briefly present ST4SQL and we present, also through some examples, its semantics with respect to the standard SQL one.
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