Current Geographic Information Systems (GISs) are inadequate for performing spatial analysis, since they force users to formulate their often vague requests by means of crisp selection conditions on spatial data. In fact, SQL extended to support spatial analysis is becoming the de facto standard for GISs; however, it does not allow the formulation of flexible queries. Based on these considerations, we propose the extension of SQL/Spatial in order to make it flexible. Flexibility is obtained by allowing the expression of linguistic predicates defining soft spatial and non-spatial selection conditions admitting degrees of satisfaction. Specifically, this paper proposes an extension of the basic SQL SELECT operator; proposes the definition of some spatial functions to compute gradual topological, distance, and directional properties of spatial objects; introduces a new operator for defining linguistic predicates over spatial properties, and reports the related formal semantics