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Introduction to XQuery. Bun Yue Professor, CS/CIS UHCL. W3C Recommendations. http://www.w3.org/TR/xquery/ : W3C XQuery http://www.w3.org/TR/xmlquery-use-cases : XQuery use cases. http://www.w3.org/TR/xquery-operators/ : XQuery and XPath functions.

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Introduction to xquery

Introduction to XQuery

Bun Yue

Professor, CS/CIS

UHCL


W3c recommendations

W3C Recommendations

  • http://www.w3.org/TR/xquery/: W3C XQuery http://www.w3.org/TR/xmlquery-use-cases: XQuery use cases.

  • http://www.w3.org/TR/xquery-operators/: XQuery and XPath functions.

  • http://www.w3.org/TR/xpath-datamodel/: XQuery 1.0 and XPath 2.0 Data Model.

  • http://www.w3.org/TR/xpath20/: XPath 2.0.

  • http://www.w3.org/TR/xmlschema-1/: XML Schema Part 1: Structures.

  • http://www.w3.org/TR/xmlschema-2/: XML Schema Part 2: datatypes.


Introduction

Introduction

  • XQuery is designed for effectively query and retrieve information from a diversified XML sources.

  • The XML sources can be one or more XML documents.

  • XQuery is derived from Quilt, and has borrowed features from XPath, XQL, SQL, etc.


Introduction1

Introduction

  • It is a functional language where a query is an expression.

  • There are three faces of the XQuery languages:

    • A "surface" syntax that programmers may probably use.

    • An XML-based syntax that machine may probably use (XQueryX).

    • A formal semantic that XQuery engine implementators use.


Introduction2

Introduction.

  • XQuery 1.0 extends XPath 2.0.

  • The type system of XQuery is based on XML Schema.

  • A limitation of XQuery:

    • No update or insert.

  • The basic building block of XQuery is expressions. (In this sense, like SQL, XQuery is not a full programming language.)


Comparing to sql

Comparing to SQL


Review of xpath 2 0

Review of XPath 2.0

  • The value of an expression is a sequence, which is an ordered list of items.

  • An item can be a node or of atomic value.

  • There are 7 node types:

    • Document

    • Element

    • Attribute

    • Comment

    • Text

    • Processing Instruction

    • Namespace


Xqueryx

XQueryX

For doc("census.xml")//person[@job="Athlete"]

the corresponding XQueryX can be:

<?xml version="1.0"?>

<q:query xmlns:q="http://www.w3.org/2001/06/xqueryx"> 

<q:step q:axis="descendant-or-self">   

<q:function q:name="document">     

<q:constant q:datatype="xs:string">census.xml</q:constant>

</q:function>   

<q:predicatedExpr>     

<q:identifier>person</q:identifier>     

<q:predicate>

<q:function q:name="equals">

<q:step q:axis="attribute">

<q:identifier>job</q:identifier>               </q:step>               <q:constant q:datatype="xs:string">Athlete</q:constant>          </q:function>      </q:predicate>   

</q:predicatedExpr> 

</q:step>

</q:query>


Data types

Data Types

  • XQuery is strongly typed.

  • XQuery types are based on

    • XML Schema: using the namespace prefix xs and url: http://www.w3.org/2001/XMLSchema.

    • XPath functions and operators: using the namespace prefix xdt and url: http://www.w3.org/2004/07/xpath-datatypes


Types

Types


Types1

Types

  • xdt:untyped is used to denote element nodes not yet validated.

  • xdt:untypedAtomic is used to denote atomic types that has not been assigned a more specific type.


Query

Query

  • A query in XQuery is an expression for

    • reading XML documents or fragments and

    • returning a sequence of well-formed XML fragments

  • Everything in XQuery is an expression that is evaluated to a value.


Query expressions

Query expressions

  • Some common forms of XQuery expressions are (these appear in most tutorials):

    • path expressions

    • element constructors

    • FLWR or FLOWR (pronounced as "flower") expressions

    • list expressions

    • conditional expressions

    • quantified expressions

    • datatype expressions


More queries

More Queries

  • Examples of other expressions include:

    • primary expressions

    • sequence expressions

    • arithmetic expressions

    • logical expressions

    • comparison expressions

    • sorting expressions

    • validate expressions


Comments

Comments

  • XQuery comments are embedded within (: and :).


Functions

Functions

  • Supports a collection of about 200 built-in operators and functions to be used within expressions.

  • Input functions in XQuery include doc() and collection(). They are used to identify the sources of the XML documents.


Input functions

Input Functions

  • Input functions:

    • doc()

    • collection().


Prolog

Prolog

  • XQuery may have prologs for declarations. Examples:

    • Variable declarations

    • Function declarations

    • Base-URI declarations

    • Version declarations

    • Module import


Variable declarations

Variable Declarations

  • Format: declare variable $name = expression;

  • E.g.

    declare variable $a := doc("census.xml")//person ;


Path expressions

Path Expressions

  • XQuery 1.0 is a superset of XPath 2.0.

  • An XPath expression is also an XQuery expression


Editix

Editix

  • Use “View > Windows > XQuery Builder”

  • For XQ files, use “XSLT/XQuery > Transform using an XQuery Request…”

    • Specify source xq file, xml file and output file.

    • Use .xml extension. If you use .txt extension, only text node contents are output.


Examples

Examples

declare base-uri "whatever-path";

doc("bib.xml")/*

Return basically bib.xml.


Example

Example

doc("bib.xml")//*

Return many nodes (in a sequence).

  • Results are not well-formed.


Examples1

Examples

doc("bib.xml")//book[@year]

count(doc("census.xml")//person)


Element constructors

Element Constructors

  • Element constructors can be used to construct XML elements.

  • If the name, attributes, and content of the element are all constants, the element constructor is based on standard XML notation and is called a direct element constructor (W3C).


Example1

Example

The XQuery

<authors>

<author>Bun Yue</author>

</authors>

returns

<authors>

<author>Bun Yue</author>

</authors>


Element constructors1

Element Constructors

  • XQuery expressions can be embedded in the direct element constructors within a pair of curly braces, {}.

  • For the characters '{' and '}', use '{{' and '}}' respectively.

  • XQuery expressions may be separated by commas.


Example2

Example

<authors><author>Bun Yue</author>{ doc("bib.xml")//author }</authors>

Adds Bun Yue to the authors of bib.xml.


Computed constructors

Computed Constructors

  • Computed constructors can also be used to declare nodes:

    • Use the keywords element, attribute, document, text, processing-instruction, comment, or namespace to declare the type of the nodes.

    • Specify the node names for those node types with names (element, attribute, processing instruction, and namespace nodes)

    • Use a pair of braces to define the content expressions.

    • Note the use of commas to separate expressions in the context.


Example from w3c

Example (from W3C)

element book {

attribute isbn {"isbn-0060229357" },

element title { "Harold and the Purple Crayon"},

element author {

element first { "Crockett" },

element last {"Johnson" }

}

}


Example result

Example (result)

<book isbn="isbn-0060229357">    <title>Harold and the Purple Crayon</title>    <author>      <first>Crockett</first>      <last>Johnson</last>    </author>

</book>


Dynamic element names

Dynamic Element Names

  • Computed expressions can be used to create elements with dynamic names.


Example3

Example

<result>

{ for $author in doc("bib.xml")//author

return

element {$author/last/text()} {

$author/first

}

}

</result>


Example result1

Example Result

<?xml version="1.0" encoding="UTF-8"?>

<result>

<Stevens>

<first>W.</first>

</Stevens>

<Stevens>

<first>W.</first>

</Stevens>

<Abiteboul>

<first>Serge</first>

</Abiteboul>

<Buneman>

<first>Peter</first>

</Buneman>

<Suciu>

<first>Dan</first>

</Suciu>

</result>


Example4

Example

  • Note that <first> is a child element. See the difference of:

    <result>

    { for $author in doc("bib.xml")//author

    return

    element {$author/last/text()} {

    $author/first/text()

    }

    }

    </result>


Example5

Example

  • This example may also result in a runtime error (as the value of <last> may not be suitable for a QName.


Flwor expressions

FLWOR expressions

  • FLWOR expressions are one of the most important constructs in XQuery.

  • You may compare with the SELECT statement of SQL.


Flwor w3c

FLWOR (W3C)

[42]    FLWORExpr    ::=    (ForClause | LetClause)+ WhereClause? OrderByClause? "return" ExprSingle

[43]    ForClause    ::=    "for" "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle ("," "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle)*

[45]    LetClause    ::=    "let" "$" VarName TypeDeclaration? ":=" ExprSingle ("," "$" VarName TypeDeclaration? ":=" ExprSingle)*

[123]    TypeDeclaration    ::=    "as" SequenceType

[44]    PositionalVar    ::=    "at" "$" VarName

[46]    WhereClause    ::=    "where" Expr

[47]    OrderByClause    ::=    ("order" "by" | "stable" "order" "by") OrderSpecList

[48]    OrderSpecList    ::=    OrderSpec ("," OrderSpec)*

[49]    OrderSpec    ::=    ExprSingle OrderModifier

[50]    OrderModifier    ::=    ("ascending" | "descending")? (("empty" "greatest") | ("empty" "least"))? ("collation" StringLiteral)?


Flwor

FLWOR

  • FLWOR expressions allow:

    • For: Iteration through items in XPath 2.0 sequences. Create a tuple stream where each tuple contains a distinct binding for each variable to a distinct value.

    • Let: Variables binding

    • Where: Predicate application for inclusion in the iteration.

    • Order by: Ordering data set for the iteration.

    • Return: Constructing new result for returning.


For and let

For and Let

  • The for and let clauses produces a tuple stream.

  • A tuple consists of one or more bound variables.

  • A variable begins with the prefix $.

  • A bound variable is one that has been assigned a value.


Example6

Example

declare base-uri “whatever”;

let $a := doc("bib.xml")//author

return

<authors>

{ $a }

</authors>


Example results

Example Results

<?xml version="1.0" encoding="UTF-8"?>

<authors>

<author>

<last>Stevens</last>

<first>W.</first>

</author>

<author>

<last>Stevens</last>

<first>W.</first>

</author>

</authors>


Example note

Example Note

  • In this example:

    • The tuple stream is composed of only one tuple.

    • The variable $b in this tuple is bound to the node sequence of 5 <author> nodes.


Example7

Example

for $a in doc("bib.xml")//author

return

<authors>

{ $a }

</authors>


Example result2

Example Result

<?xml version="1.0" encoding="UTF-8"?>

<authors>

<author>

<last>Stevens</last>

<first>W.</first>

</author>

</authors>

<authors>

<author>

<last>Stevens</last>

<first>W.</first>

</author>

</authors>

</authors>


Example notes

Example Notes

  • In this example:

    • The tuple stream is composed of only five tuples.

    • The variable $b in this tuple is bound to one <author> node at a time.


Example8

Example

for $a in doc("bib.xml")//author,

$b in doc("bib.xml")//author

return

<count/>


Example result3

Example Result

<?xml version="1.0" encoding="UTF-8"?>

<count/>

<count/>

<count/>

<count/>

… (: 25 counts :)


Example note1

Example Note

  • The tuple stream is composed of only 25 tuples.

  • The 25 tuples are:

    • ($a: <author><last>Stevens</last><first>W.</first></author>, $b: <author><last>Stevens</last><first>W.</first></author>)

    • ($a: <author><last>Stevens</last><first>W.</first></author>, $b: <author><last>Stevens</last><first>W.</first></author>)

    • ($a: <author><last>Stevens</last><first>W.</first></author>, $b: <author><last>Abiteboul</last><first>Serge</first></author>)


Example9

Example

for $a in doc("bib.xml")//author,

$b in $a/last

return

<count />


Example result4

Example Result

<?xml version="1.0" encoding="UTF-8"?>

<count/>

<count/>

<count/>

<count/>

<count/>


Example note2

Example Note

  • The tuple stream is composed of only 5 tuples.

  • The 5 tuples are:

    • ($a: <author><last>Stevens</last><first>W.</first></author>, $b: <last>Stevens</last)

    • ($a: <author><last>Stevens</last><first>W.</first></author>, $b: <last>Stevens</last)

    • ($a: <author><last>Abiteboul</last><first>Serge</first></author>, $b: <last>Abiteboul</last)


Example10

Example

for $a in doc("bib.xml")//author,

$b in doc("bib.xml")//author

where $a = $b

return

<result><alast>{ $a/last/text() }</alast><blast>{ $b/last/text() }</blast></result>


Example result5

Example Result

<?xml version="1.0" encoding="UTF-8"?>

<result>

<alast>Stevens</alast>

<blast>Stevens</blast>

</result>

… (: three more times. :)

<result>

<alast>Abiteboul</alast>

<blast>Abiteboul</blast>

</result>

<result>

<alast>Buneman</alast>

<blast>Buneman</blast>

</result>

<result>

<alast>Suciu</alast>

<blast>Suciu</blast>

</result>


Example note3

Example Note

  • The tuple stream is composed of only 7 tuples.

  • The 7 tuples are:

    • ($a: <author><last>Stevens</last><first>W.</first></author>, $b: <author><last>Stevens</last><first>W.</first></author>) (: 4 times)

    • ($a: <author><last>Abiteboul</last><first>Serge</first></author>, $b: <author><last>Abiteboul</last><first>Serge</first></author>)


Example11

Example

<figlist>

{for $f in doc("tree-data.xml")//figure

return

<diagram>

{ $f/@* }

{ $f/title }

</diagram>}

</figlist>


Example result6

Example Result

<?xml version="1.0" encoding="UTF-8"?>

<figlist>

<diagram height="400" width="400">

<title>Traditional client/server architecture</title>

</diagram>

<diagram height="200" width="500">

<title>Graph representations of structures</title>

</diagram>

<diagram height="250" width="400">

<title>Examples of Relations</title>

</diagram>

</figlist>


Example note4

Example Note

  • There are three tuples in the tuple stream of the for clause. Each tuple has one variable: $f, which is bounded to each of the three <figure> elements in the input xml contents respectively.

  • { $f/@* } returns the attributes of the original <figure> elements, which will be put as attributes of the output <figure> element.


Example12

Example

<authors>

{ fn:string-join(for $a in doc("tree-data.xml")//author return $a/text(), ", ") }

</authors>


Example result7

Example Result

<?xml version="1.0" encoding="UTF-8"?>

<authors>Serge Abiteboul, Peter Buneman, Dan Suciu</authors>


Example note5

Example Note

  • fn:string-join takes two arguments:

    • A sequence of string, and

    • A string join separator


Example13

Example

<book>

{for $f in doc("tree-data.xml")//figure

return

<figure>

{ attribute size { [email protected] * [email protected] } }

</figure>}

</book>


Example result8

Example Result

<?xml version="1.0" encoding="UTF-8"?>

<book>

<figure size="160000"/>

<figure size="100000"/>

<figure size="100000"/>

</book>


Example14

Example

<book>

{ for $f in doc("tree-data.xml")//figure

let $size := [email protected] * [email protected]

order by $size

return

<figure>

{ attribute size { $size } }

</figure>}

</book>


Example result9

Example Result

<?xml version="1.0" encoding="UTF-8"?>

<book>

<figure size="100000"/>

<figure size="100000"/>

<figure size="160000"/>

</book>


Exercise 1

Exercise #1

  • Use bib.xml, Show all books published by Addison Wesley.

    <bib>    <book>        <title>TCP/IP Illustrated</title>        <author><last>Stevens</last><first>W.</first></author>    </book>    <book>        <title>Advanced Programming in the Unix environment</title>        <author><last>Stevens</last><first>W.</first></author>    </book></bib>


Exercise 2

Exercise #2

  • All books by Addison-Wesley using different format:

    <bib>    <book author="W. Stevens">        <name>TCP/IP Illustrated</name>    </book>    <book author="W. Stevens">        <name>Advanced Programming in the Unix environment</name>    </book>

    </bib>


Exercise 3

Exercise #3

  • All books written by W. Stevens ordered by years:

    <result>

    <book-title>Advanced Programming in the Unix environment</book-title>

    <book-title>TCP/IP Illustrated</book-title>

    </result>


Exercise 4

Exercise #4

  • All books written by W. Stevens ordered by years in descending order:

    <result>

    <book-title>TCP/IP Illustrated</book-title>

    <book-title>Advanced Programming in the Unix environment</book-title>

    </result>


Exercise 5

Exercise #5

  • Use ft2.xml, return every <person> with its <first> and <last> child elements. Add a child element <numEmail> to include the number of email addresses.

      <result>    <person>      <first>Boris</first>      <last>Becker</last>      <numEmail>2</numEmail>    </person>…

      </result>


Exercise 6

Exercise #6

  • Return all <person> elements with all attributes. The body of the <person> element should be the name of the person in the format of first name and then last name. For ft2.xml, it returns:

      <result>    <person ssn="s123456789" gender="M" luckynumber="7">Boris Becker</person>    <person ssn="s111222333" gender="F" luckynumber="6">Valerie Becker</person>    <person ssn="s123123123" gender="M" luckynumber="4">Chris Becker</person>    <person ssn="s222333444" gender="F">Julie Becker</person>    <person ssn="s555987323" gender="M">John Becker</person>    <person ssn="s887667545" gender="F">Mary Becker</person>

    </result>


Exercise 7

Exercise #7

  • Return all pairs of <first> elements of persons with the same last name, not including pairing with oneself. Each pair of result is embedded in an element with the last name of the persons as the element name. For ft2.xml, it returns:

    <result>   <Becker><first>Boris</first><first>Valerie</first></Becker>   <Becker><first>Boris</first><first>Chris</first></Becker>   <Becker><first>Boris</first><first>Julie</first></Becker>   <Becker><first>Boris</first><first>John</first></Becker>   <Becker><first>Boris</first><first>Mary</first></Becker>   <Becker><first>Valerie</first><first>Boris</first></Becker>

    </result>


Exercise 8

Exercise #8

  • Convert all text nodes to <text /> and all elements with name x to <element name="x" />. For ft2.xml, it returns:

      <result>     <element name="familytree"/>    <text/>    <text/>    <element name="meta"/>

    </result>


Function declarations

Function Declarations

  • XQuery allows user-defined functions in the prolog.

    [26]   FunctionDecl   ::=   "declare" "function" QName "(" ParamList? ")" ("as" SequenceType)? (EnclosedExpr | "external")

    [27]   ParamList   ::=   Param ("," Param)*

    [28]   Param   ::=   "$" QNameTypeDeclaration?

    [118]   TypeDeclaration   ::=   "as" SequenceType


Example factorial i

Example: factorial($i)

declare function local:factorial($i as xs:integer) as xs:integer

{ if ($i < 0) then 0

else if ($i = 0) then 1

else $i * local:factorial($i - 1)

};

local:factorial(6)


Functions1

Functions

  • There is a ; after the function declaration.

  • The namespace prefix local is used for user-defined functions. XQuery predefines the namespace prefix local to the namespace http://www.w3.org/2004/07/xquery-local-functions, and reserves this namespace for use in defining local functions.

  • The types of the arguments and return values should be sequence types.


Types2

Types

  • Sequence type can be:

    • empty(), or

    • ItemType OccurrenceIndicator?

  • OccurrenceIndicator can be +, ? or *.

  • Item type can be:

    • item()

    • atomic type, or

    • kind test.


Kind tests

Kind Tests

  • Important kind tests include

    • node()

    • text()

    • comment()

    • processing-instruction(): with optional name argument.

    • element test

    • attribute test


Element tests

Element Tests

  • Example of element tests are:

    • element(*)

    • element(familytree)

    • element(man, personType)


Functions2

Functions

  • Writing XQuery functions:

    • Functional programming.

    • Many are recursive in nature.

    • Beware of types of parameters and return values.


Example from w3c1

Example from W3C

declare function local:depth($e as node()) as xs:integer

{

(: A node with no children has depth 1 :)

(: Otherwise, add 1 to max depth of children :)

if (fn:empty($e/*)) then 1

else fn:max(for $c in $e/* return local:depth($c)) + 1

};

<result>

{ local:depth(doc("ft2.xml"))

}

</result>


Exercise 9

Exercise #9

  • Write an XQuery function to count the number of elements in an element node (including itself). Try to use a recursive solution.


Exercise 10

Exercise #10

For XML document such as ft2.xml, write a function that returns all child person nodes with parent of social security number $ssn.


Questions

Questions


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