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).The following rules shall be adhered to:- Every geometry type shall derive from this abstract type.- Every geometry element (i.e. an element of a geometry type) shall be directly or indirectly in the substitution group of AbstractGeometry.
The attribute gml:id supports provision of a handle for the XML element representing a GML Object. Its use is mandatory for all GML objects. It is of XML type ID, so is constrained to be unique in the XML document within which it occurs.
<complexType name="AbstractGeometryType" abstract="true"><annotation><documentation>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). The following rules shall be adhered to: - Every geometry type shall derive from this abstract type. - Every geometry element (i.e. an element of a geometry type) shall be directly or indirectly in the substitution group of AbstractGeometry.</documentation></annotation><complexContent><extension base="gml:AbstractGMLType"><attributeGroup ref="gml:SRSReferenceGroup"/></extension></complexContent></complexType>