Define your own function
Simple function File: Query.xquery declare namespace math = "http://java2s.com"; declare function math:add($op1 as xs:integer, $op2 as xs:integer) as xs:integer { $op1 + $op2 }; declare variable $op1 as xs:integer := 1; declare variable $op2 as xs:integer := 2; <add> <op1>{$op1}</op1> <op2>{$op2}</op2> <result>{math:add($op1, $op2)}</result> </add> Output: <?xml version="1.0" encoding="UTF-8"?> <add> <op1>1</op1> <op2>2</op2> <result>3</result> </add>