XPath and XQuery 4.0 Tutorial

XML Prague 2026

Juri Leino — Jinntec GmbH

#AMA

Thx

• Intro
• brief Overview of QT4CG activities
• Summaries of changed specs
  • XPath
  • Functions and operators
  • XQuery
  • XSLT*

Agenda

• Process (nested) maps and arrays as easily as node trees
• Full processing of (deep) JSON as a target Syntax and function additions to improve ease of use
• Minimal backwards incompatibility

Moving from 3.1 to 4.0

A late breaking change...

Nodes

Trees of Nodes

<root>
  <child>a</child>
  <child />
</root>

document
- element(root)
  - element(child)
    - text(a)
  - element(child)

$document//child

(
  <child>a</child>,
  <child />
)

XNodes

XTrees

XNodes

GNodes

JNodes

XNodes

GNodes

JTree

XTree

GTree

JNodes

parent a reference to the parent JNode in the tree

value the value of the array member or map entry

key the map key or array index

position needed to handle "mixed" content

JNodes

jtree()

jnode-value()​

jnode-key()

jnode-position()

JNodes

      [ "a", "b", "c"]
      /*[1]
      /..
      /*[last()]
      /string()

JNodes

jtree([ "a", "b", "c"])
      /*[1]
      /..
      /*[last()]
      /string()

JNodes

{
  "fr": {
    "capital": "Paris", 
    "languages": [ "French" ] }, 
  "de": {
     "capital": "Berlin",
     "languages": [ "German" ] }
}
//languages

JNodes

{
  "fr": {
    "capital": "Paris", 
    "languages": [ "French" ] }, 
  "de": {
     "capital": "Berlin",
     "languages": [ "German" ] }
}
//child:get("languages")

JNodes

 {
  "fr": {
    "capital": "Paris", 
    "languages": [ "French" ] }, 
  "de": {
     "capital": "Berlin",
     "languages": [ "German" ] }
}
//languages/jnode-value() 

JNode

XNodes

Fiddle

https://fiddle.basex.org

QT4 Tutorial

XPath

XPath

The map-Keyword

   { "this": "is", "a": "map" }

map

XPath

The map-Keyword

   { "this": "is", "a": "map" }

XPath

Lookups with ?

{ "test 1": 10 }?("test 1")

{ 1: 10 }?1

{ "test": 10 }?test

XPath

Lookups with ?

{ "test 1": 10 }?("test 1")

XPath

Lookups with ?

{ "test 1": 10 }? "test 1"​

XPath

Lookups with ?

{ "test 1": 10 }?($property)

XPath

Lookups with ?

{ "test 1": 10 }? $property

XPath

Arrow operator

EXPR => my:f() => my:g()​

my:g(my:f(EXPR))​

XPath

Arrow operator

XPath

Arrow operator

XPath

ArrowBang

XPath

Arrow shortfalls

function argument order

XPath

Arrow shortfalls

RHS has to be a function call

XPath

Pipeline operator

XPath

string templates

XPath

fn-Keyword

XPath

Focus Functions

XPath

Conditionals I

XPath

Conditionals II

XPath

type checks I

XPath

type checks I

XPath

type checks II

XPath

type checks II

XPath

type checks III

XPath

type checks IV

XPath

Destructuring I

XPath

Destructuring I

XPath

Destructuring II

XPath

Destructuring III

XPath

Methods

Functions and Operators

Position Parameter

fn:filter(
  $input as item()*,
  $predicate as fn(item(), xs:integer) as xs:boolean?
) as item()*

Optional Parameters

declare function my:fn ($a, $b) { $a, $b };

declare function my:fn ($a) { my:fn($a, ()) };

Optional Parameters

declare function my:fn ($a, $b) { $a, $b };

declare function my:fn ($a) { my:fn($a, ()) };

my:fn(12)

Named Parameters

declare function local:many-parameters (
  $a := 1, $b := 1, $c := 1, $d :=1
) {
  $a + $b * $c * $d
};

local:many-parameters()

Named Parameters

declare function local:many-parameters (
  $a := 1, $b := 1, $c := 1, $d :=1
) {
  $a + $b * $c * $d
};

local:many-parameters(c:=2, a:=0)

Options maps/records

doc($uri, $options)

parse-csv("a|b|c", {
    "field-delimiter": "|"
})

XQuery

Context I

• context item -> context value
• set context default value(s)

declare context value as document() external :=
  document { (: the default :) }

Context II

declared namespaces: xs, fn, err

declare namespace array="???";

array:filter([1,-3,4,0], fn {
  math:abs(.) > 1
})

Context II

array:filter([1,-3,4,0], fn {
  math:abs(.) > 1
})

declared namespaces: xs, fn, err, map, array, math

Context II

declare option output:method "json";
array:filter([1,-3,4,0], fn {
  math:abs(.) > 1
})

declared namespaces: xs, fn, err, map, array, math, output

switch I

switch II

Declare Custom Types

declare type my:binary
  as (xs:base64binary | xs:hexBinary);

enum

declare type my:color as enum(
  "red", "green", "blue"
)​

Declare Custom Types

record

declare type my:rectangle as record(
  height as xs:decimal,
  width as xs:decimal
)​

Declare Custom Types

record

declare record my:rectangle (
  height as xs:decimal,
  width as xs:decimal
)​

Declare Custom Types

extendable record

declare record my:rectangle (
  height as xs:decimal,
  width as xs:decimal,
  *
)​

Declare Custom Types

record with a method

declare record my:rectangle (
  height as xs:decimal,
  width as xs:decimal,
  area as fn(my:rectangle) as xs:decimal := fn ($self) {
    $self?height × $self?width
  }
)​

Declare Custom Types

record with a method that is a focus function

declare record my:rectangle (
  height as xs:decimal,
  width as xs:decimal,
  area as fn(my:rectangle) as xs:decimal := fn {
    ?height × ?width
  }
)​

Declare Custom Types

try-catch with error map

try {
    error(QName("local:error"), 
        "I can't let you do that, Dave.",
        { "custom": true() })
} catch * {
    trace($err:map)
}

Errors

{
  'code': 'local:error',
  'description': 'I can't let you do that, Dave.',
  'value': { "custom": true() },
  'lineNumber': 2,
  'columnNumber': 4,
  'module': 'my-module.xq',
  'stacktrace': …,
   ⋮
}

Errors

try-catch with finally

try {
    let $i := 0 return 1 div $i
} catch * {
    $err:description
} finally {

    message(`1 div {$i}`)
}

Finally

XSLT

<xsl:stylesheet
  xmlns:array="http://www.w3.org/2005/xpath-functions/array"
  xmlns:err="http://www.w3.org/2005/xqt-errors"
  xmlns:fn="http://www.w3.org/2005/xpath-functions"
  xmlns:map="http://www.w3.org/2005/xpath-functions/map"
  xmlns:math="http://www.w3.org/2005/xpath-functions/math"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  exclude-result-prefixes="#all"
  version="4.0"
>
...

<xsl:choose>
  <xsl:when test="$n ge 0">
    <xsl:sequence select="1"/>
  </xsl:when>
  <xsl:otherwise>
    <xsl:sequence select="-1"/>
  </xsl:otherwise>
</xsl:choose>

<xsl:if test="$n ge 0" then="1" else="-1" />

<xsl:variable name="n" select="a"/>
<xsl:choose>
  <xsl:when test="$n = (1, 2, 3, 4)">
    <xsl:sequence select="../small"/>
  </xsl:when>
  <xsl:when test="$n = (5 to 20)">
    <xsl:sequence select="../medium"/>
  </xsl:when>
  <xsl:otherwise>
    <xsl:sequence select="../large"/>
  </xsl:otherwise>
</xsl:choose>

Switch

Text

Switch

<xsl:stylesheet
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  fixed-namespaces="#default"
  exclude-result-prefixes="#all"
  version="4.0">
...

<xsl:choose>
  <xsl:when test="$n lt $low">
    <xsl:sequence select="../below"/>
  </xsl:when>
  <xsl:when test="$n gt $high">
    <xsl:sequence select="../above"/>
  </xsl:when>
  <xsl:otherwise>
    <xsl:sequence select="../within"/>
  </xsl:otherwise>
</xsl:choose>

<xsl:choose>
  <xsl:when test="$n lt $low" select="../below"/>
  <xsl:when test="$n gt $high" select="../above"/>
  <xsl:otherwise select="../within"/>
</xsl:choose>

<xsl:function
  name="f:book-to-json"
  as="map(*)">
  <xsl:param name="book" as="element(book)">
  <xsl:sequence select="{
    'title' : string($book/title),
    'author' : array { $book/author ! string() },
    'date' :
        let $d := $book/publication
        return
          if (current-date() lt xs:date($d))
          then $d
          else 'Don&apos;t release'
  }"/>
</xsl:function>

<xsl:function
  name="f:book-to-json"
  as="map(*)">
  <xsl:param name="book" as="element(book)">
  <xsl:sequence select="{ 'title' : string($book/title), 'author' : array { $book/author ! string() }, 'date' : let $d := $book/publication return if (current-date() lt xs:date($d)) then $d else 'Don&apos;t release' }"/>
</xsl:function>

<xsl:function
  name="f:book-to-json"
  as="map(*)">
  <xsl:param name="book" as="element(book)">
  <xsl:select>
  {
    'title' : string($book/title),
    'author' : array { $book/author ! string() },
    'date' :
        let $d := $book/publication
        return
          if (current-date() lt xs:date($d))
          then $d
          else 'Don&apos;t release'
  }
  </xsl:select>
</xsl:function>

<xsl:for-each-group
  select="1 to 4, 5, 7 to 9, 10 to 12, 14, 15, 20 to 22"
  split-when="$next ne ($group[last()] + 1)">
  <group>{ current-group() }</group>
</xsl:for-each-group>

<xsl:for-each-group
  select="1 to 4, 5, 7 to 9, 10 to 12, 14, 15, 20 to 22"
  split-when="$next ne ($group[last()] + 1)">
  <group>{ current-group() }</group>
</xsl:for-each-group>

<xsl:for-each-group
  select="1 to 4, 5, 7 to 9, 10 to 12, 14, 15, 20 to 22"
  split-when="$next ne ($group[last()] + 1)">
  <group>{ current-group() }</group>
</xsl:for-each-group>

<group>1 2 3 4 5</group>
<group>7 8 9 10 11 12</group>
<group>14 15</group>
<group>20 21 22</group>

<xsl:function name="f:inRange">
  <xsl:param name="n" as="element()"/>
  <xsl:param name="low" required="no" select="0"/>
  <xsl:param name="high" required="no">
    <xsl:call-template name="findNumberLimit"/>
  </xsl:param>
  <!-- the actual function -->
</xsl:function>

101 Fun things to do with QT4

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juri@jinntec.de