The required n attribute is the number of Id elements in this array.
Source
<xs:element name="ToolIds" type="ArrayReferenceType" minOccurs="0"><xs:annotation><xs:documentation>The optional ToolIds element is a list of the QIF ids of measurement tools associated with the carriage.</xs:documentation></xs:annotation></xs:element>
The required id attribute is the QIF id of the measurement resource, used for referencing.
Source
<xs:complexType name="CarriageType"><xs:annotation><xs:documentation>The CarriageType defines a measurement device carriage.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="MeasurementResourceBaseType"><xs:sequence><xs:element name="ToolIds" type="ArrayReferenceType" minOccurs="0"><xs:annotation><xs:documentation>The optional ToolIds element is a list of the QIF ids of measurement tools associated with the carriage.</xs:documentation></xs:annotation></xs:element></xs:sequence></xs:extension></xs:complexContent></xs:complexType>