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about XML/Xquery/RDF

about XML/Xquery/RDF. < h1 > Bibliography </ h1 > < p > < i > Foundations of Databases </ i > Abiteboul, Hull, Vianu <br> Addison Wesley, 1995 < p > < i > Data on the Web </ i > Abiteoul, Buneman, Suciu < br > Morgan Kaufmann, 1999. < bibliography >

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about XML/Xquery/RDF

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  1. about XML/Xquery/RDF

  2. <h1> Bibliography </h1> <p> <i> Foundations of Databases </i> Abiteboul, Hull, Vianu <br> Addison Wesley, 1995 <p> <i> Data on the Web </i> Abiteoul, Buneman, Suciu <br> Morgan Kaufmann, 1999 <bibliography> <book> <title> Foundations… </title> <author> Abiteboul </author> <author> Hull </author> <author> Vianu </author> <publisher> Addison Wesley </publisher> <year> 1995 </year> </book> … </bibliography> HTML vs. XML “Self-describing” -Schema info part of the data -Good for data exchange (albeit baroque for storage)

  3. Why are Database folks so excited about XML? • XML is just a syntax for (self-describing) data • This is still exciting because • No standard syntax for relational data • With XML, we can • Translate any legacy data to XML • Can exchange data in XML format • Ship over the web, input to any application

  4. Jim Hendler XML machine accessible meaning This is what a web-page in natural language looks like for a machine

  5. < > name < > education < > CV < > work < > private Jim Hendler XML machine accessible meaning XML allows “meaningful tags” to be added toparts of the text

  6. < > < name > name <education> < > education < CV > < > CV <work> < > work <private> < > private Jim Hendler XML machine accessible meaning But to your machine, the tags look like this….

  7. Jim Hendler XML machine accessible meaning Schemas help…. < CV > …by relating common termsbetween documents private

  8. name> < > name < > <educ> education < CV > < > CV < > work <> < > <> private Jim Hendler But other people use other schemas Someone else has one like this….

  9. Jim Hendler But other people use other schemas < CV > …which don’t fit in private Moral: There is still need for ontology mapping..

  10. 11/18

  11. The X-standards… • XML: an on-the-wire representation for data • Xquery: a query language for XML • Xschema: a schema description language for XML data • RDF: a language for meta-data description • WSDL/SOAP/UDDI: languages for describing services

  12. XML Terminology • tags: book, title, author, … • start tag: <book>, end tag: </book> • elements: <book>…<book>,<author>…</author> • elements are nested • empty element: <red></red> abbrv. <red/> • an XML document: single root element well formed XML document: if it has matching tags

  13. <h1> Bibliography </h1> <p> <i> Foundations of Databases </i> Abiteboul, Hull, Vianu <br> Addison Wesley, 1995 <p> <i> Data on the Web </i> Abiteoul, Buneman, Suciu <br> Morgan Kaufmann, 1999 • <bibliography> • <book> <title> Foundations… </title> • <author> Abiteboul </author> • <author> Hull </author> • <author> Vianu </author> • <publisher> Addison Wesley </publisher> • <year> 1995 </year> • </book> • … • </bibliography> HTML describes presentation XML describes content

  14. XML Terminology • tags: book, title, author, … • start tag: <book>, end tag: </book> • elements: <book>…<book>,<author>…</author> • elements are nested • empty element: <red></red> abbrv. <red/> • an XML document: single root element well formed XML document: if it has matching tags

  15. More XML: Attributes <bookprice = “55” currency = “USD”> <title> Foundations of Databases </title> <author> Abiteboul </author> … <year> 1995 </year> </book> Attributes are single-valued --No guidance on when to use them

  16. Object identifiers More XML: Oids and References <personid=“o555”> <name> Jane </name> </person> <personid=“o456”> <name> Mary </name> <childrenidref=“o123 o555”/> </person> <personid=“o123” mother=“o456”><name>John</name> </person> oids and references in XML are just syntax

  17. TEXT More Structure XML Less Structure Structured (relational) Data XML vs. Relational Data • XML is meant as a language that supports both Text and Structured Data • Conflicting demands... • XML supports semi-structured data • In essence, the schema can be union of multiple schemas • Easy to represent books with or without prices, books with any number of authors etc. • XML supports free mixing of text and data • using the #PCDATA type • XML is ordered (while relational data is unordered)

  18. DTDs Notice that DTD is not In XML syntax…  <!DOCTYPE paper [ <!ELEMENT paper (section*)> <!ELEMENT section ((title,section*) | text)> <!ELEMENT title (#PCDATA)> <!ELEMENT text (#PCDATA)> ]> Semi- structured <paper> <section> <text> </text> </section> <section> <title> </title> <section> … </section> <section> … </section> </section> </paper>

  19. XML Schemas • More recent proposal (with XML syntax) • unifies previous schema proposals • generalizes DTDs • uses XML syntax • two documents: structure and datatypes • http://www.w3.org/TR/xmlschema-1 • http://www.w3.org/TR/xmlschema-2

  20. RDF: Meta-data Standard for Web <rdf:Descriptionabout=“www.mypage.com”> <about> birds, butterflies, snakes </about> <author> <rdf:Description> <firstname> John </firstname> <lastname> Smith </lastname> </rdf:Description> </author> </rdf:Description> Good’ol semantic networks..?

  21. Querying XML • Requirements: • Need to handle lack of schema. • We may not know much about the data, so we need to navigate the XML. • Need to support both “information retrieval” and “SQL-style” queries. • Ordered vs. un-ordered XML • “Human readable” • like SQL?  • Candidates • Many… based on conflicting requirements • XSL: Makes IR folks happy • XML-QL: Makes DB folks happy • Xquery : W3C’s attempt to make everybody (un)happy

  22. 11/20 Agenda: Xquery examples Information Integration

  23. Xquery Resources • XQuery 1.0: An XML Query Language • W3C Working Draft 20 December 2001 • XML Query Use Cases • W3C Working Draft 20 December 2001 • Microsoft .Net Xquery Language Demo • http://131.107.228.20/ • Supports querying on the documents described in the W3C Use Cases • Xquery Tutorial by Fankhauser & Wadler • www.research.avayalabs.com/user/wadler/papers/xquery-tutorial/ xquery-tutorial.pdf

  24. FLoWeR Expressions Xquery queries are made up of FLWR expressions that work on “paths” • For binds variables to nodes • Let computes aggregates • Where applies a formula to find matching elements • Return constructs the output elements Path expressions are of the form: element//element/element[attrib=value]

  25. Comparison to SQL • Look at the use case description on Xquery manual • Supports all (?) SQL style queries (with different syntax of course) [default queries in the demo] • Has support for • “construction”—outputting the answers in arbitrary XML formats (use case XMP ) • “path expressions” --- navigating the XML tree (use case seq) • Simple text queries [use case text] • Allows queries on “Tag” elements • Removes the “data/meta-data” barrier in queries • 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. [XMP use case 6]

  26. DTD for http://www.bn.com/bib.xml <!ELEMENT bib (book* )> <!ELEMENT book (title, (author+ | editor+ ), publisher, price )> <!ATTLIST book year CDATA #REQUIRED > <!ELEMENT author (last, first )> <!ELEMENT editor (last, first, affiliation )> <!ELEMENT title (#PCDATA )> <!ELEMENT last (#PCDATA )> <!ELEMENT first (#PCDATA )> <!ELEMENT affiliation (#PCDATA )> <!ELEMENT publisher (#PCDATA )> <!ELEMENT price (#PCDATA )>

  27. Example Query Query Result <bib> { for $b in /bib/book where $b/publisher = "Addison-Wesley" and $b/@year > 1991 return <book year={ $b/@year }> { $b/title } </book> } </bib> “For all books after 1991, return with Year changed from a tag to an attribute” <bib> <book year="1994"> <title>TCP/IP Illustrated</title> </book> <book year="1992"> <title>Advanced Programming in the Unix environment</title> </book> </bib>

  28. Example Query (2) • Return the books that cost more at amazon than fatbrain Let $amazon := document(http://www.amazon.com/books.xml), Let $fatbrain := document(http://www.fatbrain.com/books.xml) For $am in $amazon/books/book, $fat in $fatbrain/books/book Where $am/isbn = $fat/isbn and $am/price > $fat/price Return <book>{ $am/title, $am/price, $fat/price }<book> Join

  29. XML frenzy in the DB Community • Now that XML is there, what can we do with it? • Convert all databases from Relational to XML? • Or provide XML views of relational databases? • Develop theory of native XML databases? • Or assume that XML data will be stored in relational databases.. • Issues: What sort of storage mechanisms? What sort of indices?

  30. XML middleware for Databases • XML adapters (middle-ware) received significant attention in DB community • SilkRoute (AT&T) • Xperanto (IBM) • Issues: • Need to convert relational data into XML • Tagging (easy) • Need to convert Xquery queries into equivalent SQL queries • Trickier as Xquery supports schema querying

  31. Xquery Tutorial Craig Knoblock University of Southern California

  32. References • XQuery 1.0: An XML Query Language • W3C Working Draft 20 December 2001 • XML Query Use Cases • W3C Working Draft 20 December 2001 • Microsoft .Net Xquery Language Demo • http://131.107.228.20/ • Supports querying on the documents described in the W3C Use Cases • Xquery Tutorial by Fankhauser & Wadler • www.research.avayalabs.com/user/wadler/papers/xquery-tutorial/ xquery-tutorial.pdf

  33. DTD for http://www.bn.com/bib.xml <!ELEMENT bib (book* )> <!ELEMENT book (title, (author+ | editor+ ), publisher, price )> <!ATTLIST book year CDATA #REQUIRED > <!ELEMENT author (last, first )> <!ELEMENT editor (last, first, affiliation )> <!ELEMENT title (#PCDATA )> <!ELEMENT last (#PCDATA )> <!ELEMENT first (#PCDATA )> <!ELEMENT affiliation (#PCDATA )> <!ELEMENT publisher (#PCDATA )> <!ELEMENT price (#PCDATA )>

  34. Data for www.bn.com/bib.xml <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>

  35. Data for www.bn.com/bib.xml (cont.) <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> <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>

  36. Document References • Document can either be referenced explicitly or in the default namespace • In the Microsoft Demo • /Bib = document("http://www.bn.com/bib.xml")/bib • We will use /bib throughout, but you must use the expansion to run the demo • In Theseus the document for xquery is passed as input

  37. Projection • Return the names of all authors of books /bib/book/author = <author><last>Stevens</last><first>W.</first></author> <author><last>Stevens</last><first>W.</first></author> <author><last>Abiteboul</last><first>Serge</first></author> <author><last>Buneman</last><first>Peter</first></author> <author><last>Suciu</last><first>Dan</first></author>

  38. Project (cont.) • The same query can also be written as a for loop /bib/book/author = for $bk in /bib/book return for $aut in $bk/author return $aut = <author><last>Stevens</last><first>W.</first></author> <author><last>Stevens</last><first>W.</first></author> <author><last>Abiteboul</last><first>Serge</first></author> <author><last>Buneman</last><first>Peter</first></author> <author><last>Suciu</last><first>Dan</first></author>

  39. Selection • Return the titles of all books published before 1997 /bib/book[@year < "1997"]/title = <title>TCP/IP Illustrated</title> <title>Advanced Programming in the Unix environment</title>

  40. Selection (cont.) • Return the titles of all books published before 1997 /bib/book[@year < "1997"]/title = for $bk in /bib/book where $bk/@year < "1997" return $bk/title = <title>TCP/IP Illustrated</title> <title>Advanced Programming in the Unix environment</title>

  41. Selection (cont.) • Return book with the title “Data on the Web” /bib/book[title = "Data on the Web"] = <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>

  42. Selection (cont.) • Return the price of the book “Data on the Web” /bib/book[title = "Data on the Web"]/price = <price> 39.95</price> How would you return the book with a price of $39.95?

  43. Selection (cont.) • Return the book with a price of $39.95 for $bk in /bib/book where $bk/price = " 39.95" return $bk = <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>

  44. Construction • Return year and title of all books published before 1997 for $bk in /bib/book where $bk/@year < "1997" return <book>{ $bk/@year, $bk/title }</book> = <book year="1994"> <title>TCP/IP Illustrated</title> </book> <book year="1992"> <title>Advanced Programming in the Unix environment</title> </book>

  45. Grouping • Return titles for each author for $author in distinct(/bib/book/author/last) return <author name={ $author/text() }> { /bib/book[author/last = $author]/title } </author> = <author name="Stevens"> <title>TCP/IP Illustrated</title> <title>Advanced Programming in the Unix environment</title> </author> <author name="Abiteboul"> <title>Data on the Web</title> </author> …

  46. Join • Return the books that cost more at amazon than fatbrain Let $amazon := document(http://www.amazon.com/books.xml), Let $fatbrain := document(http://www.fatbrain.com/books.xml) For $am in $amazon/books/book, $fat in $fatbrain/books/book Where $am/isbn = $fat/isbn and $am/price > $fat/price Return <book>{ $am/title, $am/price, $fat/price }<book>

  47. Example Query 1 <bib> { for $b in /bib/book where $b/publisher = "Addison-Wesley" and $b/@year > 1991 return <book year={ $b/@year }> { $b/title } </book> } </bib> What does this do?

  48. Result Query 1 <bib> <book year="1994"> <title>TCP/IP Illustrated</title> </book> <book year="1992"> <title>Advanced Programming in the Unix environment</title> </book> </bib>

  49. Example Query 2 <results> { for $b in document("http://www.bn.com/bib.xml")/bib/book, $t in $b/title, $a in $b/author return <result> { $t } { $a } </result> } </results>

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