Nikos dimitrakas – IS4/2i1242/2i4042 spring 2007 1 XML Query Languages Database Systems (4th...

nikos dimitrakas – IS4/2i1242/2i4042 spring 2007

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XML Query Languages

Database Systems (4th edition)

Chapter 30.5, 30.3.3, 30.3.4

Articles & Excerpts

XML Query Languages * 2

XQuery

Computer Environment Tutorials

DB2 & XML

Querying XML Data with XQuery


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XML Query Languages

Languages for querying data stored inside XML structures

•XPath•XSLT•XQuery•XML/SQL (SQL 2003c)•Proprietary languages (IBM, Oracle, etc.)•…


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XPath

• Path expressions for navigating through XML structures

• Possible to set conditions and use wildcards

• Also includes many functions

• Example:– /Book[@Price=500]/Author/@Name


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XSLT• Enables transformations between different XML

structures (mostly used for XML to HTML transformations)

• Example:

<books><book title=“x”>

<author name=“a”/></book><book title=“y”>

<author name=“b”/></book>

</books>

<authors><author>a</author><author>b</author>

</authors>

<xsl:template match=“/”><authors><xsl:for-each select=“books/book/author”>

<author><xsl:value-of select=“name”></author></xsl:for-each></authors>

</xsl:template>


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XQuery

• Query language for XML

• Combines XPath and FLWOR expressions– FLWOR: For Let Where Order by Return

• Supports use of all the functions included in XPath

• Inspired by many other languages like SQL, OQL, Lorel, etc.


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XML/SQL

• SQL 2003 (ISO standard)– Support for XML in “relational” databases

• Storage

• Querying through XQuery

– Support for constructing XML from relational data with SQL


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Proprietary Languages

• Support for XML data and transformations between XML and relational data.

• IBM:– SQL UDFs: Extract-functions, Update-function– Mapping schemes: DAD-files

• Oracle:– SQL UDFs: Extract-functions, existsNode, etc.

• Others


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Example<Test Place="Kista" Deadline="2002.09.21"> <Description version="2.1"> This test is about the effects of computer games on the human brain </Description> <Phase Status="finished" Index="2" Date="2001.03.11"> <Details>Choose the computer games to be used for the test</Details> <Results>Age of Empires</Results> <Results>Flight Simulator</Results> <Results>Tetris</Results> </Phase> <Phase Status="started" Index="3"> <Details>Let users try the computer games</Details> <Results> Many users find Flight Simulator hard due to 3D environment and multiple controls </Results> </Phase> <Phase Status="cancelled" Index="1" Date="2001.01.09"> <Details>Try to get funding from EU</Details> </Phase> <Phase Status="not-started" Index="4"> <Details>Present the results of the test</Details> </Phase></Test>


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XPath

• /• //• @• /element/@attribute• /elementX//elementY• Wildcards * nodes()• Predicates: [predicate]:

– /element[1]– /element[@attribute=value]

• . and .. (current node and parent node)• | (concatenation)


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XPath Examples

• Any Results node:– //Results

• Any Phase that is cancelled– //Phase[@status=‘cancelled’]

• The Date of a Phase that has a Results– //Phase/Results/../@Date

• The Results of the Phase with Index 2 or 3– /Test/Phase[@Index=2]/Results |

/Test/Phase[@Index=3]/Results


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XPath Axes

• child, ancestor, descendant, parent– /Test/child::Phase (equivalent to /Test/Phase)– //Results/ancestor::Test


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XQuery

• For– Loop through a list/set of nodes/values

• Let– Assignments

• Where– Conditions

• Order By– Sort the result

• Return– Construct an output structure


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XQuery

• FLWOR expressions can be nested.

• No clause is compulsory.

• XPath expressions can be used in any clause

• The result can be a valid XML structure, but it doesn’t have to be.

• The function doc() can be used to define the input (XML source), or the execution environment can define an input context.


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XQuery

• Variables start with $:– for $a in //Book/Author– let $n := $a/@Name

• Sets:– for $x in (1, 2, 3)– let $y := (1, 2, 3)

• Evaluating expressions:– Enclose the expression in { }:– <result>{$x*3}</result>


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XQuery – Multiple results

• One result per value in the loop created by the for clause:for $x in (1,2,3)

return <value>{$x}</value>

• Place the result in a new result:<result>{

for $x in (1,2,3)

return <value>{$x}</value>

}</result>


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XQuery/XPath functions

• Sequence functions:– distinct-values(s)– min(s), max(s), sum(s), avg(s)– empty(s), exists(s)– union(s1,s2), instersect(s1,s2), except(s1,s2)– concat(s1,s2)

• Node functions:– name(n), local-name(n), node-name(n)


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• String functions:– matches(s, regexp)– concat(s1,s2)– starts-with(s1,s2), ends-with(s1,s2),

contains(s1,s2) – substring(s, start), substring(s, start, length)– lower-case(s), upper-case(s)– replace(s, pattern, replacement)– tokenize(s, pattern)


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• Other functions:– doc(URI)

– not(e)

– several date/time functions

– several numeric functions

– data(ns) – Sequence of nodes to sequence of atomic values

– number(n) – The value of a node as a number or NaN

– string(n) – The value of the node as a string

– current-time(), current-date(), current-dateTime()


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XQuery/XPath operators

• +, -, *, div, mod

• =, !=, >, <, <=, >=

• eq, ne, lt, le, gt, ge

• or, and, not

• is, >>, <<


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XQuery functions

• element()– /element() (similar to /*)

• attribute()– /Test/attribute() (similar to /Test/@*)

• node() (follows the standard??)– /node() – element nodes and text nodes– /@node() – attribute nodes


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XQuery – Computed Constructors

• element– element name value:

let $a := “a”, $b := 2

return <x>{element {$a} {$b}}</x>

• attribute– attribute name value:

let $a := “a”, $b := 2

return <x>{attribute {$a} {$b}}</x>


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XQuery – Conditionals

• if-then-elsefor $a in (1 to 5)

return

if ($a mod 2 = 0)

then <even>{$a}</even>

else <odd>{$a}</odd>


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XQuery – Quantifiers

• somefor $a in /Testwhere some $b in $a/Phase/@Status satisfies string($b) = "finished"return $a/Description

• everyfor $a in /Testwhere every $b in $a/Phase/@Status satisfies

string($b) = "finished"return $a/Description


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XQuery – Nesting

• One result becomes the source of another expression:for $x in distinct-values

(for $a in (1 to 5), $b in (1 to 5)

return <sum>{$a + $b}</sum>)

return <unique>{$x}</unique>


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XML/SQL

• Functions for generating XML documents as SQL results:– XMLELEMENT– XMLFOREST– XMLATTRIBUTES– XMLAGG– XMLCONCAT


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Example table structure and dataPERSONpid name yearofbirth

1 John Higgins 19752 Steven Hendry 19733 Mathew Stevens 19824 Ronnie O'Sullivan 19805 Ken Doherty 19746 Steve Davis 19607 Paul Hunter 1983

CARlicencenumber color brand model year owner

ABC123 black NISSAN Cherry 1995 1CCD457 blue FIAT Forza 2001 2DKL998 green SAAB 9000C 1998 3RSQ199 black NISSAN Micra 1999 4WID387 red FIAT Nova 2003 5ROO197 blue SAAB 900i 1982 3TYD226 black NISSAN Cherry 1990 1PTF357 red VOLVO V70 2001 6


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XMLELEMENT• Creates an XML element with a specified name and content:

SELECT XMLELEMENT(NAME "Person", name)FROM Person

<Person>John Higgins</Person>

<Person>Steven Hendry</Person>

<Person>Mathew Stevens</Person>

<Person>Ken Doherty</Person>

<Person>Steve Davis</Person>

<Person>Paul Hunter</Person>

<Person>Ronnie O'Sullivan</Person> (1 result row per element)

DB2: SELECT xml2clob(XMLELEMENT(NAME "Person", name)) FROM Person


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XMLATTRIBUTES• Creates an XML attributes to be placed inside an XML element:

SELECT XMLELEMENT(NAME "Person", XMLATTRIBUTES(yearofbirth), name)FROM Person

<Person YEAROFBIRTH="1975">John Higgins</Person> <Person YEAROFBIRTH="1973">Steven Hendry</Person>

<Person YEAROFBIRTH="1982">Mathew Stevens</Person><Person YEAROFBIRTH="1974">Ken Doherty</Person><Person YEAROFBIRTH="1960">Steve Davis</Person><Person YEAROFBIRTH="1983">Paul Hunter</Person><Person YEAROFBIRTH="1980">Ronnie O'Sullivan</Person>


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XMLATTRIBUTES• SELECT XMLELEMENT(NAME "Person", XMLATTRIBUTES(yearofbirth AS "Year"), name) FROM Person

<Person Year="1975">John Higgins</Person>

<Person Year="1973">Steven Hendry</Person>

<Person Year="1982">Mathew Stevens</Person>

<Person Year="1974">Ken Doherty</Person>

<Person Year="1960">Steve Davis</Person>

<Person Year="1983">Paul Hunter</Person>

<Person Year="1980">Ronnie O'Sullivan</Person>


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XMLATTRIBUTES• SELECT XMLELEMENT(NAME "Person", XMLATTRIBUTES(yearofbirth AS "Year", name))

FROM Person

<Person Year="1975" NAME="John Higgins"></Person>

<Person Year="1973" NAME="Steven Hendry"></Person>

<Person Year="1982" NAME="Mathew Stevens"></Person>

<Person Year="1974" NAME="Ken Doherty"></Person>

<Person Year="1960" NAME="Steve Davis"></Person>

<Person Year="1983" NAME="Paul Hunter"></Person>

<Person Year="1980" NAME="Ronnie O'Sullivan"></Person>


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XMLCONCAT

• Combine more elements as a sequence of element. • This would give us two columns:

SELECT XMLELEMENT(NAME "Name", name), XMLELEMENT(NAME "Year", yearofbirth) FROM Person

• This would give us one column in the result:SELECT XMLCONCAT(XMLELEMENT(NAME "Name", name), XMLELEMENT(NAME "Year", yearofbirth))FROM Person


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XMLCONCAT<Name>John Higgins</Name><Year>1975</Year>

<Name>Steven Hendry</Name><Year>1973</Year>

<Name>Mathew Stevens</Name><Year>1982</Year>

<Name>Ken Doherty</Name><Year>1974</Year>

<Name>Steve Davis</Name><Year>1960</Year>

<Name>Paul Hunter</Name><Year>1983</Year>

<Name>Ronnie O'Sullivan</Name><Year>1980</Year>

• Still multiple rows though


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XMLFOREST• Create multiple elements:

SELECT XMLFOREST(name AS "Name", yearofbirth AS "Year")FROM Person

<Name>John Higgins</Name><Year>1975</Year>

<Name>Steven Hendry</Name><Year>1973</Year>

<Name>Mathew Stevens</Name><Year>1982</Year>

<Name>Ken Doherty</Name><Year>1974</Year>

<Name>Steve Davis</Name><Year>1960</Year>

<Name>Paul Hunter</Name><Year>1983</Year>

<Name>Ronnie O'Sullivan</Name><Year>1980</Year>


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Combinations• Or make this more complete by combining different functions:

SELECT XMLELEMENT(NAME "Person", XMLATTRIBUTES(pid AS "ID"), XMLFOREST(name AS "Name", yearofbirth AS "Year"))

FROM Person

<Person ID="1"><Name>John Higgins</Name><Year>1975</Year></Person>

<Person ID="2"><Name>Steven Hendry</Name><Year>1973</Year></Person>

<Person ID="3"><Name>Mathew Stevens</Name><Year>1982</Year></Person>

<Person ID="5"><Name>Ken Doherty</Name><Year>1974</Year></Person>

<Person ID="6"><Name>Steve Davis</Name><Year>1960</Year></Person>

<Person ID="7"><Name>Paul Hunter</Name><Year>1983</Year></Person>

<Person ID="4"><Name>Ronnie O'Sullivan</Name><Year>1980</Year></Person>


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XMLAGG

• Grouping many rows into one result. Can be used together with a GROUP BY clause.

• Put all the persons in one result row:

SELECT XMLAGG(XMLELEMENT(NAME "Person", name)) FROM Person<Person>John Higgins</Person><Person>Steven Hendry</Person><Person>Mathew Stevens</Person><Person>Ken Doherty</Person><Person>Steve Davis</Person><Person>Paul Hunter</Person><Person>Ronnie O'Sullivan</Person>

• One result row! (though not well-formed XML)


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Combinations

• Put all the persons in one Persons element:SELECT XMLELEMENT(NAME "Persons", XMLAGG(XMLELEMENT(NAME "Person", name)))

FROM Person<Persons><Person>John Higgins</Person><Person>Steven Hendry</Person><Person>Mathew Stevens</Person><Person>Ken Doherty</Person><Person>Steve Davis</Person><Person>Paul Hunter</Person><Person>Ronnie O'Sullivan</Person></Persons>

• One result row! (AND well-formed XML)


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XMLAGG with GROUP BY• One row per group:

SELECT XMLELEMENT(NAME "Color", XMLATTRIBUTES(color), XMLAGG(XMLELEMENT(NAME "Car", licencenumber)))

FROM Car GROUP BY color

<Color COLOR="black"><Car>ABC123</Car><Car>TYD226</Car><Car>RSQ199</Car></Color>

<Color COLOR="blue"><Car>CCD457</Car><Car>ROO197</Car></Color>

<Color COLOR="green"><Car>DKL998</Car></Color>

<Color COLOR="red"><Car>WID387</Car><Car>PTF357</Car></Color>


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Aggregates without XMLAGGSELECT XMLELEMENT(NAME "Color", XMLATTRIBUTES(color, COUNT(*) as "Amount")) FROM Car

GROUP BY color

<Color COLOR="black" Amount="3"></Color>

<Color COLOR="blue" Amount="2"></Color>

<Color COLOR="green" Amount="1"></Color>

<Color COLOR="red" Amount="2"></Color>


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DB2's extra XML support

• Store XML documents

• Query data inside the XML structures

• Change data inside the XML structures

• Validate XML documents against DTDs

• Decompose XML documents into tables


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Query XML data

• Path expressions– simple version of XPath

• extract-functions– two functions for each data type

• 1 singleton function, e.g. extractInteger

• 1 plural function, e.g. extractIntegers


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Update XML data

• Path expressions– simple version of XPath

• update-function– replaces a specified path with a new value– returns the entire XML document


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More Information

• XPath– http://www.w3schools.com/xpath/

• XQuery– http://www.w3schools.com/xquery/– http://www.stylusstudio.com/xml_tutorial.html

• XML/SQL– http://docs.openlinksw.com/virtuoso/

composingxmlinsql.html– http://www.stylusstudio.com/sqlxml_tutorial.html

Nikos dimitrakas – IS4/2i1242/2i4042 spring 2007 1 XML Query Languages Database Systems (4th...

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