THE XML REVOLUTION - TECHNOLOGIES FOR THE FUTURE WEB

List expressions

XQuery expressions manipulate lists of values, for which many operators are supported:

constant lists: (7, 9, <thirteen/>)
integer ranges: i to j
XPath expressions, like all named children of the context node: name
concatenation: ,
set operators: | (or union), intersect, except
functions: remove, index-of, count, avg, max, min, sum, distinct-values ...

When lists are viewed as sets:

XML nodes are compared on node identity
duplicates are removed
the order is preserved

The following query lists each publisher and the average price of their books:

for $p in distinct-values(document("bib.xml")//publisher) let $a := avg(document("bib.xml")//book[publisher = $p]/price) return <publisher> <name>{ $p/text() }</name> <avgprice>{ $a }</avgprice> </publisher>

Compare this with the verbose XQueryX syntax.