Spatial Integrity Constraints in 3D City Models: from Conceptual Definition to SQL Implementation

Several different models have been defined in literature for the definition of 3D city models, from CityGML to Inspire (Annex 3 - Buildings). Such models include a geometrical representation of features together with a semantical classification of them. The semantical characterization of objects encapsulates important meaning and spatial relations which are defined only implicitly or through natural language, such as buildings shall be disjoint or in touch, or a window surface shall be contained in the building boundary. The problem of ensuring the coherence between geometric and semantic information is well known in literature. Many attempts exist which try to extent the OCL language in order to represent spatial constraints for an UML model. However, this approach requires a deep knowledge of the OCL language and the implementation of ad-hoc procedures for the validation of constraints defined at conceptual level. The aim of this paper is the development of a set of templates for expressing spatial 3D constraints between features which does not require any particular knowledge of a formal language. Moreover, the constraints instantiated from these templates can be automatically translated into validation SQL queries, without the need for ad-hoc implementations.