One of the challenges raised by the construction of the semantic Web lies in the analysis and management of complex relationships (thematic, spatial and temporal) connecting several resources. The automatic discovery of such relations will improve the current capabilities of existing search engines. Spatial information plays an important role in the resources available on the Web, thus, integrating spatial criteria into queries addressed to search engines would increase the power of expression of the formulation and will improve the search result. However, ontology languages of the semantic Web, OWL in particular, still do not have the expected specific characteristics for a well adapted representation and exploitation of spatial data. We present here ONTOAST, a spatial ontology modeling and reasoning system. ONTOAST manages qualitative spatial relations which can be used to express spatial queries. It also handles the inference of new qualitative relations, thus increasing the spatial...