Generic (user defined) city objects may be used to model features which are not covered explicitly by the CityGML schema. Generic objects must be used with care; they shall only be used if there is no appropiate thematic class available in the overall CityGML schema. Oherwise, problems concerning semantic interoperability may arise. As subclass of _CityObject, a generic city object inherits all attributes and relations, in particular an id, names, external references, and generalization relations. Generic (user defined) attributes may be used to represent attributes which are not covered explicitly by the CityGML schema. Generic attributes must be used with care; they shall only be used if there is no appropiate attribute available in the overall CityGML schema. Oherwise, problems concerning semantic interoperability may arise. A generic attribute has a name and a value, which has further subclasses (IntAttrribute, StringAttribute, ...).