Database handle for the object. It is of XML type ID, so is constrained to beunique in the XML document within which it occurs. An external identifier for the object inthe form of a URI may be constructed using standard XML and XPointer methods. This is doneby concatenating the URI for the document, a fragment separator, and the value of the idattribute.
Source
<complexType name="AbstractComponentObjectBaseType" abstract="true"><annotation><documentation>Base type for all component objects where gml:AbstractGML is restricted to only allow for an optional gml:id.</documentation></annotation><complexContent><restriction base="gml:AbstractGMLType"><sequence><sequence><element minOccurs="0" ref="gml:description"/><element minOccurs="0" ref="gml:identifier"/></sequence></sequence></restriction></complexContent></complexType>