Advisor: Prof. Zaniolo

1
XML Query Language

• Advisor Prof. Zaniolo
• Hung-chih Yang
• Ling-Jyh Chen

2
Motivation

• As increasing amounts of information are stored,
  exchanged, and presented using XML, the ability
  to intelligently query XML data sources becomes
  increasingly important.
• One of the great strengths of XML is its
  flexibility in representing many different kinds
  of information from diverse sources.
• To exploit this flexibility, an XML query
  language must provide features for retrieving and
  interpreting information from these diverse
  sources.

3
Desiderata for an XML query language

• Expressive power
• Semantics
• Compositionality
• Schema
• Program manipulation

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 its the immediate ancestor
  of XQuery

5
Whats XQuery
SQL
Relational database
XML document /database
XQuery
6
Whats XQuery (cont.)

• XQuery is designed to meet the requirements
  identified by the W3C XML Query Working Group
  XML Query 1.0 Requirements and the use cases in
  XML Query Use Cases.
• XQuery is designed to be a small, easily
  implementable language.
• XQuery is flexible enough to query a broad
  spectrum of XML information sources, including
  both databases and documents.
• XQuery defines a human-readable syntax for that
  language

7
Whats Xquery (cont.)

• The basic building block of XQuery is the
  expression
• XQuery is a functional language (at least the
  spec claimed it to be)
• XQuery is a strongly-typed language

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

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

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The principal forms of XQuery expressions

• Primary
• The basic primitives of the language including
  literals, variables, function calls and the use
  of parentheses to control precedence of operation
• 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.

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The principal forms of XQuery expressions (cont.)

• Arithmetic
• Xquery provides arithmetic operators for
  addition, subtraction, multiplication, division,
  and modulus.
• Comparison
• Xquery provides 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 one of the boolean values
  true or false.

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The principal forms of XQuery expressions (cont.)

• Contructor
• Constructors can create XML structures within a
  query. There are constructors for elements,
  attributes, CDATA sections, processing
  instructions, and comments.
• FLWR
• XQuery provides a FLWR expression for iteration
  and for binding variables to intermediate
  results. This kind of expression is often useful
  for computing joins between two or more documents
  and for restructuring data. The name "FLWR",
  pronounced "flower", stands for the keywords for,
  let, where, and return, the four clauses found in
  a FLWR expression.

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The principal forms of XQuery expressions (cont.)

• Sorting
• A sorting expression provides a way to control
  the order of items in a sequence.
• Conditional
• XQuery supports a conditional expression based on
  the keywords if, then, and else.
• Quantified
• Quantified expressions support existential and
  universal quantification. The value of a
  quantified expression is always true or false.

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The principal forms of XQuery expressions (cont.)

• Datatypes
• 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.

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XQuery Example 1
Xquery Find all books with a price of 39.95

• document("bib.xml")/bib/bookprice 39.95

Result
ltbook year"2000"gt lttitlegtData on the
Weblt/titlegt ltauthorgtltlastgtAbiteboullt/lastgtltfir
stgtSergelt/firstgtlt/authorgt ltauthorgtltlastgtBunema
nlt/lastgtltfirstgtPeterlt/firstgtlt/authorgt
ltauthorgtltlastgtSuciult/lastgtltfirstgtDanlt/firstgtlt/auth
orgt ltpublishergtMorgan Kaufmann
Publisherslt/publishergt ltpricegt
39.95lt/pricegt lt/bookgt
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XQuery Example 2
XQuery Find the title of all books published
before 1995

• document("bib.xml")/bib/book_at_year lt 1995/title

Result
lttitlegtTCP/IP Illustratedlt/titlegt lttitlegtAdvanced
Programming in the Unix environmentlt/titlegt
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XQuery Example 3 (for loop)
XQuery List books published by Addison-Wesley
after 1991, including their year and title.

• ltbibgt
• for b in document("bib.xml")/bib/book
• where b/publisher "Addison-Wesley" and
  b/_at_year gt 1991
• return
• ltbook year" b/_at_year "gt
• b/title
• lt/bookgt
• lt/bibgt

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XQuery Example 3 (for loop)
Result

• ltbibgt
• ltbook year"1994"gt
• lttitlegtTCP/IP Illustratedlt/titlegt
• lt/bookgtltbook year"1992"gt
• lttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt
• lt/bookgt
• lt/bibgt

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XQuery Example 4 (Join)
XQuery For each book found at both bn.com and
amazon.com, list the title of the book and its
price from each source.

• ltbooks-with-pricesgt
• for b in document("bib.xml")//book,
• a in document("reviews.xml")//entry
• where b/title a/title
• return
• ltbook-with-pricesgt
• b/title
• ltprice-amazongt a/price
  lt/price-amazongt
• ltprice-bngt b/price lt/price-bngt
• lt/book-with-pricesgt
• lt/books-with-pricesgt

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XQuery Example 4 (Join)
Result

• ltbooks-with-pricesgt
• ltbook-with-pricesgt
• lttitlegtTCP/IP Illustratedlt/titlegt
• ltprice-amazongtltpricegt65.95lt/pricegtlt/pr
  ice-amazongt
• ltprice-bngtltpricegt 65.95lt/pricegtlt/price
  -bngt
• lt/book-with-pricesgtltbook-with-pricesgt
• lttitlegtAdvanced Programming in the
  Unix environmentlt/titlegt
• ltprice-amazongtltpricegt65.95lt/pricegtlt/pr
  ice-amazongt
• ltprice-bngtltpricegt65.95lt/pricegtlt/price-
  bngt
• lt/book-with-pricesgtltbook-with-pricesgt
• lttitlegtData on the Weblt/titlegt
• ltprice-amazongtltpricegt34.95lt/pricegtlt/pr
  ice-amazongt
• ltprice-bngtltpricegt 39.95lt/pricegtlt/price
  -bngt
• lt/book-with-pricesgt
• lt/books-with-pricesgt

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XQuery Example 5 (Grouping quantifier)
XQuery 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.

• ltresultsgt
• for a in distinct-values(document("bib.com")/
  /author)
• return ltresultgt
• a
• for b in document("http//bib
  .com")/bib/book
• where some ba in b/author
  satisfies deep-equal(ba,a)
• return b/title
• lt/resultgt
• lt/resultsgt

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XQuery Example 5 (Grouping quantifier)

• ltresultsgt
• ltresultgt
• ltauthorgt
• ltlastgtStevenslt/lastgt
• ltfirstgtW.lt/firstgt
• lt/authorgt
• lttitlegtTCP/IP Illustratedlt/titlegt
• lttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt
• lt/resultgt
• ltresultgt
• ltauthorgt
• ltlastgtAbiteboullt/lastgt
• ltfirstgtSergelt/firstgt
• lt/authorgt
• lttitlegtData on the Weblt/titlegt
• lt/resultgt
• lt/resultsgt

Result
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XQuery Example 6 (Sorting)
XQuery List the titles and years of all books
published by Addison-Wesley after 1991, in
alphabetic order.

• ltbibgt
• for b in document("www.bn.com/bib.xml")//book
  
• where b/publisher "Addison-Wesley" and
  b/_at_year gt 1991
• return
• ltbookgt
• b/_at_year
• b/title
• lt/bookgt
• sortby (title)
• lt/bibgt

24
XQuery Example 6 (Sorting)
Result

• ltbibgt
• ltbook year"1992"gt
• lttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt
• lt/bookgt
• ltbook year"1994"gt
• lttitlegtTCP/IP Illustratedlt/titlegt
• lt/bookgt
• lt/bibgt

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XQuery Example 7 (Recursion)
XQuery Convert the sample document from
"partlist" format to "parttree" format.

• define function one_level (element p) returns
  element
• ltpart partid" p/_at_partid " name"
  p/_at_name " gt
• for s in document("partlist.xml")//pa
  rt
• where s/_at_partof p/_at_partid
• return one_level(s)
• lt/partgt
• ltparttreegt
• for p in document("partlist.xml")//partempty
  (_at_partof)
• return one_level(p)
• lt/parttreegt

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XQuery Example 7 (Recursion)
Result

• ltparttreegt
• ltpart partid"0" name"car"gt
• ltpart partid"1" name"engine"gt
• ltpart partid"3" name"piston"/gt
• lt/partgt
• ltpart partid"2" name"door"gt
• ltpart partid"4" name"window"/gt
• ltpart partid"5" name"lock"/gt
• lt/partgt
• lt/partgt
• ltpart partid"10" name"skateboard"gt
• ltpart partid"11" name"board"/gt
• ltpart partid"12" name"wheel"/gt
• lt/partgt
• ltpart partid"20" name"canoe"/gt
• lt/parttreegt

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XQuery Example 8 (Sequence)
XQuery In the Procedure section of Report1, what
Instruments were used in the second Incision?

• for s in document("report1.xml")//sectionsection
  .title "Procedure"
• return (s//incision)2/instrument

Result
ltinstrumentgtelectrocauterylt/instrumentgt
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XQuery practice

• XML Query Language Demo,http//131.107.228.20
• X-Hive. Another nice-looking online
  demo,http//217.77.130.1898080/demos/xquery/inde
  x.html
• Qexo The GNU Kawa implementation of XQuery,
  http//www.gnu.org/software/qexo/

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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
  simplier 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

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Reference

• 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/
• XQuery Tutorialhttp//www.research.avayalabs.com/
  user/wadler/papers/xquery-tutorial/xquery-tutorial
  .pdf
• Don Chamberlin, Jonathan Robie, and Daniela
  Florescu, Quilt An XML Query Language for
  Heterogeneous Data Sources, WebDB 2000, Dallas,
  May 2000