I verified with Lizzie DeYoung that portions of an external standard can be referenced in a NIEM adapter. The example below is from the Geo4NIEM adapter, which references the GML Envelope element. It is important to note that the Envelope element is globally scoped and not a locally scoped element. Brian M Wilkins Lead Software Systems Engineer The MITRE Corporation < xs:complexType name =" EnvelopeType " appinfo:externalAdapterTypeIndicator =" true "> < xs:annotation > xs:documentation > A data type for an envelope, which defines an extent using a pair of positions defining opposite corners in arbitrary dimensions. The first direct position is the "lower corner" (a coordinate position consisting of all the minimal ordinates for each dimension for all points within </ xs:documentation > </ xs:annotation > < xs:complexContent > < xs:extension base =" structures:ObjectType "> < xs:sequence > < xs:element ref =" gml:Envelope " minOccurs =" 0 " maxOccurs =" unbounded "> < xs:annotation > < xs:documentation > An envelope which defines an extent using a pair of positions defining opposite corners in arbitrary dimensions. The first direct position is the "lower corner" (a coordinate position consisting of all the minimal ordinates for each dimension for all points within </ xs:documentation > </ xs:annotation > </ xs:element > </ xs:sequence > </ xs:extension > </ xs:complexContent > </ xs:complexType >