XQuery for eXist - eXist: A NoSQL Database and Application Development Platform - page 116

<GroupedItems>
<Group key= "A" >
<item> Apples </item>
<item> Apricots </item>
</Group>
<Group key= "B" >
<item> Bananas </item>
<item> Brambles </item>
</Group>
<Group key= "P" >
<item> Pears </item>
</Group>
</GroupedItems>
Other XQuery Extras
Beside eXist's support for XQuery 1.0 and the majority of XQuery 3.0, it also has a
few interesting features which are currently specific to its XQuery implementation.
The map data type proposed for XQuery 3.1
The map data type in eXist is essentially a key/value lookup table. Keys must be
atomic values (e.g., xs:string , xs:integer , xs:date , etc.). Values can be anything
from a simple numbers to complete XML documents. Here is a basic example of cre‐
ating and using a map:
let $ map1 := map {
"a" := 1 ,
"b" := <XML> this is <i> cool </i></XML>
} return
( $ map1 ( "a" ), $ map1 ( "b" ))
This will return:
1
<XML>this is <i>cool</i></XML>
Working programmatically with maps is possible through the map extension module.
This module allows you to do everything from checking for the existence of keys up
to constructing maps on the fly. Please refer to the online function documentation
for more information.
Maps are immutable, like any other XQuery variables. So, changing
a map using the functions from the map extension module (e.g.,
calling map:remove ) will create a new map.
There is also an article about maps on the eXist wiki .