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, ...).