The required n attribute is the number of Id elements in this array.
Source
<xs:element name="WeldCharacteristicDefinitionIds" type="ArrayReferenceFullType"><xs:annotation><xs:documentation>The WeldCharacteristicDefinitionIds element is a list of the QIF ids of the weld characteristic definitions.</xs:documentation></xs:annotation></xs:element>
The id attribute is the QIF id of the characteristic, used for referencing.
Source
<xs:complexType name="WeldCompoundCharacteristicDefinitionType"><xs:annotation><xs:documentation>The WeldCompoundCharacteristicDefinitionType defines information that can be common to more than one compound weld characteristic.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="WeldCharacteristicDefinitionBaseType"><xs:sequence><xs:element name="WeldCharacteristicDefinitionIds" type="ArrayReferenceFullType"><xs:annotation><xs:documentation>The WeldCharacteristicDefinitionIds element is a list of the QIF ids of the weld characteristic definitions.</xs:documentation></xs:annotation></xs:element></xs:sequence></xs:extension></xs:complexContent></xs:complexType>