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XQuery. John Annechino Steven Pow. Agenda. What is XQuery? Uses of XQuery XQuery vs. XSLT Syntax Built-In Functions FLWOR if-then-else User-Defined Functions Examples Future of XQuery References. What is XQuery?.
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XQuery John Annechino Steven Pow
Agenda • What is XQuery? • Uses of XQuery • XQuery vs. XSLT • Syntax • Built-In Functions • FLWOR • if-then-else • User-Defined Functions • Examples • Future of XQuery • References
What is XQuery? • The best way to explain XQuery is to say that XQuery is to XML what SQL is to database tables. • It is the language for querying XML data. • XQuery is a language for finding and extracting elements and attributes from XML documents. • XQuery is designed to query XML data – not just XML files, but anything that can appear as XML.
Uses of XQuery • Extract information to use in a Web Service • Query XML documents • Read data from databases and generate reports • Transform XML data • Search Web documents for relevant information
XQuery vs. XSLT • XSLT has a “processing engine” that automatically goes through the document tree and applies templates as it finds nodes • With XQuery, the the programmer is responsible for directing the process.
Syntax • Elements, attributes, and variables must be valid XML names • XQuery is built up with XPath expressions • XML Schema datatypes are used • XQuery variable is defined with a $ followed by a name • Comments are delimited by (: and :) (: this is a comment :)
books.xml <bookstore> <book category=“WEB”> <title>Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> <price>39.95</price> </book> <book category=“CHILDREN”> <title>Harry Potter</title> <author>J K. Rowling</author> <year>2005</year> <price>29.99</price> </book> </bookstore>
Built-In Functions doc(‘books.xml’)/bookstore/book[price>30] <book category=“WEB”> <title>Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> <price>39.95</price> </book> XQuery includes over 100 built-in functions
FLWOR • For – binds a variable to each item returned by the in expression • Let – allows variable assignments • Where – used to specify criteria for result • Order by – defines the sort-order • Return – specifies what is to be returned
FLWOR doc(‘books.xml’)/bookstore/book[price>30]/title <title>Learning XML</title> for $x in doc(‘books.xml’)/store/book where $x/price>30 return $x/title <title>Learning XML</title>
FLWOR <ul> { for $x in doc(“books.xml”)/bookstore/book order by $x/title return <li class="{data($x/@category)}">{data($x/title)}</li> } </ul> <ul> <li class=“CHILDREN”>Harry Potter</li> <li class=“WEB”>Learning XML</li> </ul>
if-then-else for $x in doc("books.xml")/bookstore/book return if ($x/@category="CHILDREN") then <child>{data($x/title)}</child> else <adult>{data($x/title)}</adult> <adult>Learning XML</adult> <child>Harry Potter</child>
User-Defined Functions declare function prefix:function_name($parameter AS datatype) AS returnDatatype { (: ...function code here... :) }; XQuery shares the same datatypes as XML Schema, including Date, String, Numeric, and other Misc types
User-Defined Functions declare function local:minPrice( $price as xs:decimal, $discount as xs:decimal) AS xs:decimal { let $disc := ($price * $discount) div 100 return ($price - $disc) }; <minPrice> { local:minPrice($book/price, $book/discount) } </minPrice>
Future of XQuery • XQuery is currently a Working Draft • XQuery is compatible with several W3C standards, such as XML, Namespaces, XSLT, XPath, and XML Schema • XQuery 1.0 is not yet a W3C Recommendation. Hopefully it will be a recommendation in the near future.
References • http://www.w3c.org/XML/Query.html • http://www.w3schools.com/xquery/default.asp • http://www.w3schools.com/xpath/xpath_functions.asp • http://www.xmlmind.com/qizxopen.html • XQuery: The XML Query Language, by Michael Brundage
