Spatial operators

This paper discusses issues related to the integration of spatial operators into the new generation of SQL-like query languages. Starting from spatial data models, current spatial extensions of query languages are briefly rev iewed and research directions are highlighted. A taxonomy of requirements t o be satisfied by spatial operators is proposed with emphasis on users' nee ds and on the introduction of data uncertainty support. Further, spatial op erators are classified into the three important categories of topological, projective, and metric operators and for each of them the state of the art is outlined.