The required n attribute is the number of Id elements in this array.
Source
<xs:element name="SensorIds" type="ArrayReferenceType" minOccurs="0"><xs:annotation><xs:documentation>The optional SensorIds element is a list of the QIF ids of sensors mounted on the tool.</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="ToolWithDetachableSensorsType"><xs:annotation><xs:documentation>The ToolWithDetachableSensorsType defines a tool with detachable sensors.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="ToolBaseType"><xs:sequence><xs:element name="SensorIds" type="ArrayReferenceType" minOccurs="0"><xs:annotation><xs:documentation>The optional SensorIds element is a list of the QIF ids of sensors mounted on the tool.</xs:documentation></xs:annotation></xs:element></xs:sequence></xs:extension></xs:complexContent></xs:complexType>