XQuery language

1. XQuery language Presented by: Tayeb sbihi supervised by: Dr. H. Haddouti

2. Why XQuery ?? • Other query languages are too specific • XML covers many facets of data modeling • Need a query language to reflect that

3. Why not other languages ?? • Document-oriented • XQL, XPath, XSLT • Relational • SQL • Object • OQL • Semi-structured • XML-QL, Lorel, YATL, UnQL

4. Who made it ?? • Quilt • 3 people • World Wide Web Consortium (W3C) • Query Language Working Group • XML Query Working Group

5. Who (cont.) ?? • 5 stages to W3C “Recommendation” • Working Draft • Last Call Working Draft • Candidate Recommendation • Proposed Recommendation • W3C Recommendation

6. When/Where ?? • W3C Query Language Workshop: Boston, December 1998 • First Draft: April 2001 • Working Draft: Draft 7, June 2001 • Final: ?

7. Origins XQL SQL Xpointer XSL patterns OQL XML - QL Xpath XQL - 99 Quilt XQuery

8. XML Query Requirements General: • Declarative Language • Readable XML Syntax • Protocol Independence • Standard Error Conditions • Support for Future Updates Data Model: • Based on XML Infosets • Namespace Aware • Support for XML Schema Data Types • Support Inter/Intra Document References

9. XML Query Requirements (cont.) Query Functionality: • Operators on All Data Types • Text Operators Across Element Boundaries • Hierarchies and Sequences • Combination of Data from Various Locations • Aggregation and Sorting • Combination of Operators (Queries as Operands) • Support NULL values • Preservation of Structure/Identity • Operations on Names/Schemas • Extensibility & Closure

10. What is XQuery • A language for querying XML • A human-readable syntax for an XML query language • A functional programming language • The product of the W3C’s XML Query Working Group

11. XQuery • Functional Language • Query Represented as an Expression • Expressions can be Nested without Restriction • Input/Output of an XQuery are Instances of the XML • Query Data Model • Based on OQL, SQL, XML-QL, XPath • Readable XML Syntax

12. XQuery 1.0 & XPath 2.0 XQueryX 1.0 XQuery 1.0 XPath 2.0 XQuery 1.0 & Xpath 2.0Formal Semantics XQuery 1.0 & Xpath 2.0Functions & Operators XQuery 1.0 & Xpath 2.0Data Model XQuery 1.0 & Xpath 2.0Requirements & Use Cases XML Schema 1.0 XML 1.0 Namespaces 1.0

13. . Denotes the current node. .. Denotes the parent of the current node. / Denotes the root node, or a separator between steps in a path. // Denotes descendants of the current node. @ Denotes attributes of the current node. * Denotes "any" (node with unrestricted name). [ ] Brackets enclose a Boolean expression that serves as a predicate for a given step. [n] When a predicate consists of an integer, it serves to select the element with the given ordinal number from a list of elements. Symbols

14. XQuery Expressions • Path Expressions • Element Constructors • FLWR Expressions • Expressions with Operators/Functions • Conditional Expressions • Quantified Expressions

15. Path Expression (Q) In the second chapter of the document named "zoo.xml", find the figure(s) with caption "Tree Frogs". document("zoo.xml")//chapter[2]//figure[caption = "Tree Frogs"] • First step locates the root node of a document. • Second step locates the second chapter of the document (ordinal number) • Third step finds figure elements occurring anywhere within the chapter, but retains those figure elements that have a caption with the value "Tree Frogs."

16. XQuery Element Constructor • Start/End Tag + Enclosed List of Expressions • Generate an element with a computed name that contains nested elements: <$tagname> <description> $d </description> <price> $p </price> </$tagname>

17. XQuery For Let Where Return (FLWR) • FOR and LET Clause • Generate a List of Tuples that Preserves Doc Order • WHERE Clause • Applies a Predicate to Eliminate Some Tuples • RETURN Clause • Executed on Resulting Tuples -> Ordered Output List • Syntax: FOR var IN expr WHERE expr RETURN expr LET var := expr

18. FLWR Expressions • A FLWR (pronounced "flower") expression is constructed from FOR, LET, WHERE, and RETURN clauses, which must appear in a specific order. • A FLWR expression binds values to one or more variables and then uses these variables to construct a result.

19. XML Document • <bib> • <book year="1994"> <title>TCP/IP Illustrated</title> <author><last>Stevens</last><first>W.</first></author> <publisher>Addison-Wesley</publisher> • <price> 65.95</price> </book> • <book year="1992"> <title>Advanced Programming in the Unix environment</title> <author><last>Stevens</last><first>W.</first></author> <publisher>Addison-Wesley</publisher> • <price>65.95</price> </book> • <book year="1999"> • <title>The Economics of Technology and Content for Digital TV</title> <editor> <last>Gerbarg</last><first>Darcy</first> <affiliation>CITI</affiliation> </editor> • <publisher>Kluwer Academic Publishers</publisher> <price>129.95</price> • </book> • </bib>

20. FLWR Expressions • (Q) List each publisher and the average price of its books. FOR $p IN distinct(document("bib.xml")//publisher) LET $a := avg(document("bib.xml")//book[publisher = $p]/price) RETURN <publisher> <name> {$p/text()} </name> <avgprice> {$a} </avgprice> </publisher> distinct = a function that eliminates duplicates

21. XQuery Operators and Functions • Infix/Prefix Operators • e.g., Infix Operators BEFORE and AFTER • Parenthesized Expressions • Arithmetic/Logical Operators • Collection Operators • e.g., UNION, INTERSECT, EXCEPT • Functions Can Be Defined in XQuery

22. Conditional Expressions (Q) Make a list of holdings, ordered by title. For journals, include the editor, and for all other holdings, include the author. FOR $h IN //holding RETURN <holding> {$h/title, IF ($h/@type = "Journal") THEN $h/editor ELSE $h/author } </holding> SORTBY (title)

23. If-Then-Else FOR$h IN //holding RETURN <holding> $h/title, IF$h/@type = "Journal" THEN$h/editor ELSE$h/author </holding> SORTBY (title)

24. Quantifiers • Tests for existence of some elements that satisfy a condition • Also used to test whether all elements in a collection satisfy a condition • Key words satisfies and contains

25. XQuery Quantified Expressions (Q) Find titles of books in which both sailing and windsurfing are mentioned in the same paragraph. FOR $b IN //book WHERE SOME $p IN $b//para SATISFIES (contains($p, "sailing") AND contains($p, "windsurfing")) RETURN $b/title

26. Sorting • A sequence can be ordered by means of a SORTBY clause that contains one or more "ordering expressions." (Q)List all books with price greater than $100, in order by first author; within each group of books with the same first author, list the books in order by title. document("bib.xml")//book[price > 100] SORTBY (author[1], title)

27. Sorting in XQuery <publisher_list> FOR$pINdistinct(document("bib.xml")//publisher) RETURN <publisher> <name> $p/text() </name> , FOR$bIN document("bib.xml")//book[publisher = $p] RETURN <book> $b/title , $b/@price </book> SORTBY(price DESCENDING) </publisher> SORTBY(name) </publisher_list>

28. Collections in XQuery • Ordered and unordered collections • /bib/book/author = an ordered collection • Distinct(/bib/book/author) = an unordered collection • LET$a = /bib/book $a is a collection • $b/author  a collection (several authors...) Returns: <result> <author>...</author> <author>...</author> <author>...</author> ... </result> RETURN <result> $b/author </result>

29. Collections in XQuery What about collections in expressions ?$b/@price list of n prices$b/@price * 0.7  list of n numbers$b/@price * $b/@quantity  list of n x m numbers ??$b/@price * ($b/@quant1 + $b/@quant2)  $b/@price * $b/@quant1 + $b/@price * $b/@quant2 !!

30. Group-By in Xquery ?? FOR$bIN document("http://www.bn.com")/bib/book, $yIN$b/@year WHERE$b/publisher="Morgan Kaufmann" RETURNGROUPBY $y WHERE count($b) > 10 IN <year> $y </year>  with GROUPBY count = a (aggregate) function that returns the number of elms SELECT year FROM Bib WHERE Bib.publisher="Morgan Kaufmann" GROUPBY year HAVING count(*) > 10 Equivalent SQL 

31. JOINS in Relation P (part) P_no descrip qnty S (supplier) s_no name locat SP (Supplies) p_no s_no price

32. XML documents P.XML <parts> <p_tuple> <p_no> 1 </p_no> <descrip> ABC </descrip> <qty> 100 </qty> </p_tuple> </parts> S.XML <supplier> <s_tuple> <s_no> 27 </s_no> <name> IBM </name> <locat> NY </locat> </s_tuple> </supplier> SP.XML <supplies_part> <sp_tuple> <p_no> 2 </p_no> <s_no> 24 </s_no> <price> 5.00 </price> </sp_tuple> </supplies_part>

33. JOINS in XQuery For $sp in document(“sp.xml”)//sp_tuple, $p in document(“p.xml”)//p_tuple[ p_no = $sp/p_no] $s in document(“s.xml”)//s_tuple [s_no = $sp/s_no] Return <sp_pair> { $s/name, $p/descrip } </sp_pair> sortby(name, descrip)

34. Additional Issues • Updates : not implemented • Case sensitivity: all keywords are case sensitive • Type checking: When being processed a query goes through two phases: Analysis Phase & Evaluation Phase. • During the Analysis phase type checking occurs to provide early detection of type errors and to compute the type of the result. • Querying XML documents with cycles

35. <bib> <book year="1994"> <title>TCP/IP Illustrated</title> <author><last>Stevens</last><first>W.</first></author> <publisher>Addison-Wesley</publisher> <price> 65.95</price> </book> <book year="1992"> <title>Advanced Programming in the Unix environment</title> <author><last>Stevens</last><first>W.</first></author> <publisher>Addison-Wesley</publisher> <price>65.95</price> </book> <book year="1999"> <title>The Economics of Technology and Content for Digital TV</title> <editor> <last>Gerbarg</last><first>Darcy</first> <affiliation>CITI</affiliation> </editor> <publisher>Kluwer Academic Publishers</publisher> <price>129.95</price> </book> </bib> Xml document

36. List books published by Addison-Wesley after 1991, including their year and title. <bib> { for $b in document("http://www.bn.com")/bib/book where $b/publisher = "Addison-Wesley" and $b/@year > 1991 return <book year="{ $b/@year }"> { $b/title } </book> } </bib> Xquery example 1

37. Expected Result • <bib> • <book year="1994"> • <title>TCP/IP Illustrated</title> • </book> • <book year="1992"> • <title>Advanced Programming in the Unix environment</title> • </book> • </bib>

38. Create a flat list of all the title-author pairs, with each pair enclosed in a "result" element. <results> { for $b in document("http://www.bn.com")/bib/book, $t in $b/title, $a in $b/author return <result> { $t } { $a } </result> } </results> XQuery Example 2

39. <results> <result> <title>TCP/IP Illustrated</title> <author> <last>Stevens</last> <first>W.</first> </author> Expected Results

40. For each book found at both bn.com and amazon.com, list the title of the book and its price from each source: <books-with-prices> { for $b in document("www.bn.com/bib.xml")//book, $a in document("www.amazon.com/reviews.xml")//entry where $b/title = $a/title return <book-with-prices> { $b/title } <price-amazon>{ $a/price/text() }</price-amazon> <price-bn>{ $b/price/text() }</price-bn> </book-with-prices> } </books-with-prices> XQuery example 3

41. For each book that has at least one author, list the title and first two authors, and an empty "et-al" element if the book has additional authors. <bib> { for $b in document("www.bn.com/bib.xml")//book where count($b/author) > 0 return <book> { $b/title } { for $a in $b/author[position()<=2] return $a } { if (count($b/author) > 2) then <et-al/> else () } </book> } </bib> XQuery Example 4

42. <book> <title>Data on the Web</title> <author> <last>Abiteboul</last> <first>Serge</first> </author> <author> <last>Buneman</last> <first>Peter</first> </author> <et-al/> </book> Result

43. Xquery example 5 • List the titles and years of all books published by Addison-Wesley after 1991, in alphabetic order. • <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> sort by (title) } </bib>

44. References • W3C XQuery http://www.w3.org/TR/xquery.html • W3C XML Query Use Cases http://www.w3.org/TR/xmlquery-use-cases.html • W3C XML Query Requirements http://www.w3.org/TR/xmlquery-req.html • W3C XML Query Data Model http://www.w3.org/TR/query-datamodel.html • W3C XML Query Algebra http://www.w3.org/TR/query-algebra.html

45. Q/A Session Your questions and feedback are most welcome......