From the viewpoint of Administration and more general users (not necessarily involved in construction activities), it is necessary to exchange information and knowledge between different agents and solutions to a larger scale involving urban districts or the whole city. This task concerns mainly to Knowledge Management Systems to urban scale. City Geographic Mark-up Language (GML3) is an OGC (Open Geospatial Consortium) standard data model and XML-based format for the storage and exchange of virtual 3D city models for exchanging data by using ontologies.