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="AbstractFeatureBaseType" mixed="false" abstract="true"><complexContent><restriction base="gml:AbstractFeatureType"><sequence><element ref="gml:description" minOccurs="0"/><element minOccurs="0" ref="gml:identifier"/></sequence><attribute ref="gml:id" use="required"><annotation><documentation>The id of this feature. The id must be unique within a DIGGS xml instance.</documentation></annotation></attribute><!-- 2015-04-23 PwD added per http://www.w3.org/TR/xmlschema-1/#d0e2483 Schema Component Constraint: Derivation Valid (Restriction, Complex) 3 --></restriction></complexContent></complexType>