An XML attribute uom ("unit of measure") is required, whose value is a URI which identifies the definition of a ratio scale or units by which the numeric value shall be multiplied, or an interval or position scale on which the value occurs.
<element name="Quantity" substitutionGroup="gml:AbstractScalarValue" nillable="true"><annotation><documentation>An XML attribute uom ("unit of measure") is required, whose value is a URI which identifies the definition of a ratio scale or units by which the numeric value shall be multiplied, or an interval or position scale on which the value occurs.</documentation></annotation><complexType><simpleContent><extension base="gml:MeasureType"><attribute name="nilReason" type="gml:NilReasonType"/></extension></simpleContent></complexType></element>