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XML Query Language

XML Query Language. Prepared by Prof. Zaniolo, Hung- chih Yang, Ling- Jyh Chen Modified by Fernando Farfán. Motivation. Increasing amounts of information stored, exchanged, and presented as XML. Ability to intelligently query XML data sources.

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XML Query Language

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  1. XML Query Language Prepared by Prof. Zaniolo, Hung-chih Yang, Ling-Jyh Chen Modified by Fernando Farfán

  2. Motivation • Increasing amounts of information stored, exchanged, and presented as XML. • Ability to intelligently query XML data sources. • XML strength: Flexibility representing many kinds of information from diverse sources. • XML query language must retrieve and interpret information from these diverse sources. XML Query Language Tutorial

  3. Desiderata for an XML Query Language • Expressive power • Semantics • Compositionality • Schema • Program manipulation XML Query Language Tutorial

  4. Different Query Languages for XML • XPath & XQL: path expression syntax suitable for hierarchical documents • XML-QL: binding variables and using bound variables to create new structures • SQL: SELECT-FROM-WHERE pattern for restructuring data • OQL: ODMG • Quilt: accept a lot of advantages from above XML query languages, and it’s the immediate ancestor of XQuery XML Query Language Tutorial

  5. What is XQuery Relational databases SQL XML document /databases XQuery XML Query Language Tutorial

  6. What is XQuery (cont.) • Designed to meet the requirements identified by the W3C XML Query Working Group • “XML Query 1.0 Requirements” • “XML Query Use Cases”. • Designed to be a small, easily implementable language. • Flexible enough to query a broad spectrum of XML sources (both databases and documents). • Defines a human-readable syntax for that language. XML Query Language Tutorial

  7. What is XQuery (cont.) • Expression: Basic building block. • Functional language (at least claimed by the spec.) • Strongly-typed language. XML Query Language Tutorial

  8. XQuery vs. XSLT Reinventing the Wheel? • XSLT is document-driven; XQuery is program driven. • XSLT is written in XML; XQuery is not. • An assertion (unproven): XSLT 2.0 can do everything XQuery can do. XML Query Language Tutorial

  9. XQuery Concepts • A query in XQuery is an expression that: • Reads a number of XML documents or fragments • Returns a sequence of well-formed XML fragments XML Query Language Tutorial

  10. The Principal Forms of XQuery Expressions • Primary • Literals, variables, function calls and parentheses (for control precedence). • Path • Locates nodes within a tree, and returns a sequence of distinct nodes in document order. • Sequence • An ordered collection of zero or more items, where an item may be an atomic value or a node. • An item is identical to a sequence of length one containing that item. Sequences are never nested. XML Query Language Tutorial

  11. The Principal Forms of XQuery Expressions (Cont.) • Arithmetic • Arithmetic operators for addition, subtraction, multiplication, division, and modulus. • Comparison • Four kinds of comparisons: value, general, node, and order comparisons. • Logical • A logical expression is either an AND-expression or an OR-expression. • The value of a logical expression is always a Boolean value. XML Query Language Tutorial

  12. The Principal Forms of XQuery Expressions (Cont.) • Constructor • Constructors can create XML structures within a query. • There are constructors for elements, attributes, CDATA sections, processing instructions, and comments. • FLWR • Expression for iteration and for binding variables to intermediate results. • Useful for computing joins between two or more documents and for restructuring data. • Pronounced "flower", stands for the keywords FOR, LET, WHERE, and RETURN, the four clauses found in a FLWR expression. XML Query Language Tutorial

  13. The Principal Forms of XQuery Expressions (Cont.) • Sorting expressions • Provides a way to control the order of items in a sequence. • Conditional expressions • Based on the keywords IF, THEN, and ELSE. • Quantified expressions • support existential and universal quantification. • The value of a quantified expression is always true or false. XML Query Language Tutorial

  14. The Principal Forms of XQuery Expressions (Cont.) • Data types • Runtime type checking and manipulation • Validate • A validate expression validates its argument with respect to the in-scope schema definitions, using the schema validation process described in XML Schema. XML Query Language Tutorial

  15. XQuery Example 1 • Find all books with a price of $39.95 XQuery: document("bib.xml")/bib/book[price = 39.95] Result: <book year="2000"><title>Data on the Web</title><author><last>Abiteboul</last><first>Serge</first></author><author><last>Buneman</last><first>Peter</first></author><author><last>Suciu</last><first>Dan</first></author><publisher>Morgan Kaufmann Publishers</publisher><price> 39.95</price> </book> XML Query Language Tutorial

  16. XQuery Example 2 • Find the title of all books published before 1995 XQuery: document("bib.xml")/bib/book[@year < 1995]/title Result: <title>TCP/IP Illustrated</title> <title>Advanced Programming in the Unix environment</title> XML Query Language Tutorial

  17. XQuery Example 3 (For Loop) • List books published by Addison-Wesley after 1991, including their year and title. XQuery: <bib> { for $b in document("bib.xml")/bib/book where $b/publisher = "Addison-Wesley" and $b/@year > 1991 return <book year="{ $b/@year }"> { $b/title } </book> } </bib> XML Query Language Tutorial

  18. XQuery Example 3 (For Loop) • List books published by Addison-Wesley after 1991, including their year and title… Result: <bib> <book year="1994"> <title>TCP/IP Illustrated</title> </book> <book year="1992"> <title>Advanced Programming in the Unix environment</title> </book> </bib> XML Query Language Tutorial

  19. XQuery Example 4 (Join) • For each book found at both bn.com and amazon.com, list the title of the book and its price from each source. XQuery: <books-with-prices> { for $b in document("bib.xml")//book, $a in document("reviews.xml")//entry where $b/title = $a/title return <book-with-prices> { $b/title } <price-amazon>{ $a/price }</price-amazon> <price-bn>{ $b/price }</price-bn> </book-with-prices> } </books-with-prices> XML Query Language Tutorial

  20. XQuery Example 4 (Join) • For each book found at both bn.com and amazon.com, list the title of the book and its price from each source. Result: <books-with-prices> <book-with-prices> <title>TCP/IP Illustrated</title> <price-amazon><price>65.95</price></price-amazon> <price-bn><price> 65.95</price></price-bn> </book-with-prices><book-with-prices> <title>Advanced Programming in the Unix environment</title> <price-amazon><price>65.95</price></price-amazon> <price-bn><price>65.95</price></price-bn> </book-with-prices><book-with-prices> <title>Data on the Web</title> <price-amazon><price>34.95</price></price-amazon> <price-bn><price> 39.95</price></price-bn> </book-with-prices> </books-with-prices> XML Query Language Tutorial

  21. XQuery Example 5 (Grouping + quantifier) • For each author in the bibliography, list the author's name and the titles of all books by that author, grouped inside a "result" element. XQuery: <results> { for $a in distinct-values(document("bib.com")//author) return <result> { $a } { for $b in document("http://bib.com")/bib/book where some $ba in $b/author satisfies deep-equal($ba,$a) return $b/title } </result> } </results> XML Query Language Tutorial

  22. XQuery Example 5 (Grouping + quantifier) • For each author in the bibliography, list the author's name and the titles of all books by that author, grouped inside a "result" element. Result: <results> <result> <author> <last>Stevens</last> <first>W.</first> </author> <title>TCP/IP Illustrated</title> <title>Advanced Programming in the Unix environment</title> </result> <result> <author> <last>Abiteboul</last> <first>Serge</first> </author> <title>Data on the Web</title> </result> …… </results> XML Query Language Tutorial

  23. XQuery Example 6 (Sorting) • List the titles and years of all books published by Addison-Wesley after 1991, in alphabetic order. XQuery: <bib> { for $b in document("www.bn.com/bib.xml")//book where $b/publisher = "Addison-Wesley" and $b/@year > 1991 return <book> { $b/@year } { $b/title } </book> sortby (title) } </bib> XML Query Language Tutorial

  24. XQuery Example 6 (Sorting) • List the titles and years of all books published by Addison-Wesley after 1991, in alphabetic order. Result: <bib> <book year="1992"> <title>Advanced Programming in the Unix environment</title> </book> <book year="1994"> <title>TCP/IP Illustrated</title> </book> </bib> XML Query Language Tutorial

  25. XQuery Example 7 (Recursion) • Convert the sample document from "partlist" format to "parttree" format. XQuery: define function one_level (element $p) returns element { <part partid="{ $p/@partid }" name="{ $p/@name }" > { for $s in document("partlist.xml")//part where $s/@partof = $p/@partid return one_level($s) } </part> } <parttree> { for $p in document("partlist.xml")//part[empty(@partof)] return one_level($p) } </parttree> XML Query Language Tutorial

  26. XQuery Example 7 (Recursion) • Convert the sample document from "partlist" format to "parttree" format. Result: <parttree> <part partid="0" name="car"> <part partid="1" name="engine"> <part partid="3" name="piston"/> </part> <part partid="2" name="door"> <part partid="4" name="window"/> <part partid="5" name="lock"/> </part> </part> <part partid="10" name="skateboard"> <part partid="11" name="board"/> <part partid="12" name="wheel"/> </part> <part partid="20" name="canoe"/> </parttree> XML Query Language Tutorial

  27. XQuery Example 8 (Sequence) • In the Procedure section of Report1, what Instruments were used in the second Incision? XQuery: for $s in document("report1.xml")//section[section.title = "Procedure"] return ($s//incision)[2]/instrument Result: <instrument>electrocautery</instrument> XML Query Language Tutorial

  28. XQuery Support on RDBMSs • Oracle XQuery Engine • http://www.oracle.com/technology/tech/xml/xquery/index.html • Introduction to XQuery in SQL Server 2005 • http://msdn.microsoft.com/en-us/library/ms345122(SQL.90).aspx • Query DB2 XML data with XQuery • http://www.ibm.com/developerworks/data/library/techarticle/dm-0604saracco/ • DataDirect: Data Integration Suite – MySQL Database Support • http://www.datadirect.com/products/data-integration/datasources/databases/mysql/index.ssp XML Query Language Tutorial

  29. Conclusion • XQuery is a simple substitution of XSLT, JSP, ASP, Servlet, CGI, PHP, etc. • XQuery programs can accomplish most tasks of other tools aforementioned, and yet is much simpler to learn and easier to write. • Possible direction is to extend XQuery for UPDATE and INSERT to an XML database • Still lack of support from industry till now XML Query Language Tutorial

  30. References • Jonathan Pinnock, et al. “Professional XML, 2nd edition”, ISBN: 1861005059, WROX Publishers, 2001 • Serge Abiteboul, Peter Buneman and Dan Suciu, “Data on the Web: from Relations to Semistructured Data and XML”, ISBN 1-55860-622-X, Morgan Kaufmann Publishers, 2000 • World Wide Web Consortium, “XQuery 1.0. An XML Query Language”, W3C Working Draft, Apr. 30, 2002 • World Wide Web Consortium, “XML Path Language (XPath) Version 1.0”, W3C Recommendation, Nov. 16, 1999 • Qexo: The GNU Kawa implementation of XQuery, http://www.gnu.org/software/qexo/ • Don Chamberlin, Jonathan Robie, and Daniela Florescu, “Quilt: An XML Query Language for Heterogeneous Data Sources”, WebDB 2000, Dallas, May 2000 XML Query Language Tutorial

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