All geometry elements are derived directly or indirectly from this abstract supertype. A geometry element may have an identifying attribute (gml:id), one or more names (elements identifier and name) and a description (elements description and descriptionReference) . It may be associated with a spatial reference system (attribute group gml:SRSReferenceGroup).<br/>The following rules shall be adhered to:<br/>- Every geometry type shall derive from this abstract type.<br/>- Every geometry element (i.e. an element of a geometry type) shall be directly or indirectly in the substitution group of AbstractGeometry.<br/>