File: Data.xml
<inventory id="inv0001" date="2008-12-19" loc="USA">
<car model="A" id="0001" quantity="1" color="navy"/>
<car model="B" id="0002" quantity="1"/>
<car model="B" id="0003" quantity="2"/>
<car model="C" id="0004" quantity="1" color="white"/>
<car model="C" id="0004" quantity="1" color="gray"/>
<car model="A" id="0001" quantity="1" color="black"/>
</inventory>
File: Query.xquery
declare namespace functx = "http://www.wbex.ru";
declare function functx:min-non-empty-string
($stringSeq as xs:string*) as xs:string? {
min($stringSeq[. != ""])
};
(: Example call :)
functx:min-non-empty-string(doc("Data.xml")//car/@model)
Output:
<?xml version="1.0" encoding="UTF-8"?>A