gml:AbstractCurveType is an abstraction of a curve to support the different levels of complexity. The curve may always be viewed as a geometric primitive, i.e. is continuous.
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="AbstractCurveType" abstract="true"><annotation><documentation>gml:AbstractCurveType is an abstraction of a curve to support the different levels of complexity. The curve may always be viewed as a geometric primitive, i.e. is continuous.</documentation></annotation><complexContent><extension base="gml:AbstractGeometricPrimitiveType"/></complexContent></complexType>