about XMLXqueryRDF

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about XML/Xquery/RDF
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HTML vs. XML

• lth1gt Bibliography lt/h1gt
• ltpgt ltigt Foundations of Databases lt/igt
• Abiteboul, Hull, Vianu
• ltbrgt Addison Wesley, 1995
• ltpgt ltigt Data on the Web lt/igt
• Abiteoul, Buneman, Suciu
• ltbrgt Morgan Kaufmann, 1999

• ltbibliographygt
• ltbookgt lttitlegt Foundations lt/titlegt
• ltauthorgt Abiteboul lt/authorgt
• ltauthorgt Hull lt/authorgt
• ltauthorgt Vianu lt/authorgt
• ltpublishergt Addison Wesley
  lt/publishergt
• ltyeargt 1995 lt/yeargt
• lt/bookgt
• lt/bibliographygt

Self-describing -Schema info part of the
data -Good for data exchange (albeit
baroque for storage)
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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

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XML ? machine accessible meaning
Jim Hendler
This is what a web-page in natural language
looks like for a machine
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XML ? machine accessible meaning
Jim Hendler
XML allows meaningful tags to be added toparts
of the text
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XML ? machine accessible meaning
Jim Hendler
But to your machine, the tags look like this.
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XML ? machine accessible meaning
Jim Hendler
Schemas help.
lt CV gt
by relating common termsbetween documents
private
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But other people use other schemas
Jim Hendler
Someone else has one like this.
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But other people use other schemas
Jim Hendler
lt CV gt
which dont fit in
private
Moral There is still need for
ontology mapping..
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11/18
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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

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XML Terminology

• tags book, title, author,
• start tag ltbookgt, end tag lt/bookgt
• elements ltbookgtltbookgt,ltauthorgtlt/authorgt
• elements are nested
• empty element ltredgtlt/redgt abbrv. ltred/gt
• an XML document single root element

well formed XML document if it has matching tags
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lth1gt Bibliography lt/h1gt ltpgt ltigt Foundations of
Databases lt/igt Abiteboul, Hull, Vianu
ltbrgt Addison Wesley, 1995 ltpgt ltigt Data on
the Web lt/igt Abiteoul, Buneman, Suciu
ltbrgt Morgan Kaufmann, 1999
ltbibliographygt ltbookgt lttitlegt Foundations
lt/titlegt ltauthorgt Abiteboul
lt/authorgt ltauthorgt Hull
lt/authorgt ltauthorgt Vianu
lt/authorgt ltpublishergt Addison
Wesley lt/publishergt ltyeargt 1995
lt/yeargt lt/bookgt lt/bibliographygt
HTML describes presentation
XML describes content
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XML Terminology

• tags book, title, author,
• start tag ltbookgt, end tag lt/bookgt
• elements ltbookgtltbookgt,ltauthorgtlt/authorgt
• elements are nested
• empty element ltredgtlt/redgt abbrv. ltred/gt
• an XML document single root element

well formed XML document if it has matching tags
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More XML Attributes

• ltbook price 55 currency USDgt
• lttitlegt Foundations of Databases lt/titlegt
• ltauthorgt Abiteboul lt/authorgt
• ltyeargt 1995 lt/yeargt
• lt/bookgt

Attributes are single-valued --No
guidance on when to use them
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More XML Oids and References
Object identifiers

• ltperson ido555gt ltnamegt Jane lt/namegt lt/persongt
• ltperson ido456gt ltnamegt Mary lt/namegt
• ltchildren
  idrefo123 o555/gt
• lt/persongt
• ltperson ido123 mothero456gtltnamegtJohnlt/namegt
• lt/persongt

oids and references in XML are just syntax
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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)

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DTDs
Notice that DTD is not In XML syntax ?
lt!DOCTYPE paper lt!ELEMENT paper
(section)gt lt!ELEMENT section ((title,section)
text)gt lt!ELEMENT title (PCDATA)gt
lt!ELEMENT text (PCDATA)gt gt
Semi- structured
ltpapergt ltsectiongt lttextgt lt/textgt lt/sectiongt
ltsectiongt lttitlegt lt/titlegt ltsectiongt
lt/sectiongt
ltsectiongt lt/sectiongt
lt/sectiongt lt/papergt
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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

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RDF Meta-data Standard for Web

• ltrdfDescription aboutwww.mypage.comgt
• ltaboutgt birds, butterflies, snakes
  lt/aboutgt
• ltauthorgt ltrdfDescriptiongt
• ltfirstnamegt John
  lt/firstnamegt
• ltlastnamegt Smith
  lt/lastnamegt
• lt/rdfDescriptiongt
• lt/authorgt
• lt/rdfDescriptiongt

Goodol semantic networks..?
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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 W3Cs attempt to make everybody (un)happy

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11/20

• Agenda
• Xquery examples
• Information Integration

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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/xque
  ry-tutorial/ xquery-tutorial.pdf

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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/elementattribvalue

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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
• constructionoutputting 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

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DTD for http//www.bn.com/bib.xml

• lt!ELEMENT bib (book )gt
• lt!ELEMENT book (title, (author editor ),
  publisher, price )gt
• lt!ATTLIST book year CDATA REQUIRED gt
• lt!ELEMENT author (last, first )gt
• lt!ELEMENT editor (last, first, affiliation )gt
• lt!ELEMENT title (PCDATA )gt
• lt!ELEMENT last (PCDATA )gt
• lt!ELEMENT first (PCDATA )gt
• lt!ELEMENT affiliation (PCDATA )gt
• lt!ELEMENT publisher (PCDATA )gt
• lt!ELEMENT price (PCDATA )gt

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Example Query
Query
Result

• ltbibgt
• for b in /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
• For all books after 1991,
• return with Year changed from
• a tag to an attribute

ltbibgt ltbook year"1994"gt lttitlegtTCP/IP
Illustratedlt/titlegt lt/bookgt ltbook
year"1992"gt lttitlegtAdvanced Programming in
the Unix environmentlt/titlegt lt/bookgt lt/bibgt
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Example Query (2)

• Return the books that cost more at amazon than
  fatbrain
• Let amazon document(http//www.amazon.com/book
  s.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 gt fat/price
• Return ltbookgt am/title, am/price, fat/price
  ltbookgt

Join
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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?

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XML middleware for Databases

• XML adapters (middle-ware) received significant
  attention in DB community
• SilkRoute (ATT)
• 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

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Xquery Tutorial

• Craig Knoblock
• University of Southern California

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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/xque
  ry-tutorial/ xquery-tutorial.pdf

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DTD for http//www.bn.com/bib.xml

• lt!ELEMENT bib (book )gt
• lt!ELEMENT book (title, (author editor ),
  publisher, price )gt
• lt!ATTLIST book year CDATA REQUIRED gt
• lt!ELEMENT author (last, first )gt
• lt!ELEMENT editor (last, first, affiliation )gt
• lt!ELEMENT title (PCDATA )gt
• lt!ELEMENT last (PCDATA )gt
• lt!ELEMENT first (PCDATA )gt
• lt!ELEMENT affiliation (PCDATA )gt
• lt!ELEMENT publisher (PCDATA )gt
• lt!ELEMENT price (PCDATA )gt

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Data for www.bn.com/bib.xml

• ltbibgt
• ltbook year"1994"gt
• lttitlegtTCP/IP Illustratedlt/titlegt
• ltauthorgtltlastgtStevenslt/lastgtltfirstgtW.lt/firstgtlt/aut
  horgt
• ltpublishergtAddison-Wesleylt/publishergt
• ltpricegt 65.95lt/pricegt
• lt/bookgt
• ltbook year"1992"gt
• lttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt ltauthorgtltlastgtStevenslt/lastgtltf
  irstgtW.lt/firstgtlt/authorgt
• ltpublishergtAddison-Wesleylt/publishergt
• ltpricegt65.95lt/pricegt
• lt/bookgt

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

• ltbook year"2000"gt
• lttitlegtData on the Weblt/titlegt
• ltauthorgtltlastgtAbiteboullt/lastgtltfirstgtSergelt/firstgt
  lt/authorgt
• ltauthorgtltlastgtBunemanlt/lastgtltfirstgtPeterlt/firstgtlt/
  authorgt
• ltauthorgtltlastgtSuciult/lastgtltfirstgtDanlt/firstgtlt/auth
  orgt
• ltpublishergtMorgan Kaufmann Publisherslt/publishergt
  
• ltpricegt 39.95lt/pricegt
• lt/bookgt
• ltbook year"1999"gt
• lttitlegtThe Economics of Technology and Content
  for Digital TVlt/titlegt
• lteditorgt ltlastgtGerbarglt/lastgtltfirstgtDarcylt/firstgt
  ltaffiliationgtCITIlt/affiliationgt lt/editorgt
• ltpublishergtKluwer Academic Publisherslt/publishergt
  
• ltpricegt129.95lt/pricegt
• lt/bookgt
• lt/bibgt

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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

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Projection

• Return the names of all authors of books
• /bib/book/author
• ltauthorgtltlastgtStevenslt/lastgtltfirstgtW.lt/firstgtlt/aut
  horgt
• ltauthorgtltlastgtStevenslt/lastgtltfirstgtW.lt/firstgtlt/aut
  horgt
• ltauthorgtltlastgtAbiteboullt/lastgtltfirstgtSergelt/firstgt
  lt/authorgt
• ltauthorgtltlastgtBunemanlt/lastgtltfirstgtPeterlt/firstgtlt/
  authorgt
• ltauthorgtltlastgtSuciult/lastgtltfirstgtDanlt/firstgtlt/auth
  orgt

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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
• ltauthorgtltlastgtStevenslt/lastgtltfirstgtW.lt/firstgtlt/aut
  horgt
• ltauthorgtltlastgtStevenslt/lastgtltfirstgtW.lt/firstgtlt/aut
  horgt
• ltauthorgtltlastgtAbiteboullt/lastgtltfirstgtSergelt/firstgt
  lt/authorgt
• ltauthorgtltlastgtBunemanlt/lastgtltfirstgtPeterlt/firstgtlt/
  authorgt
• ltauthorgtltlastgtSuciult/lastgtltfirstgtDanlt/firstgtlt/auth
  orgt

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Selection

• Return the titles of all books published before
  1997
• /bib/book_at_year lt "1997"/title
• lttitlegtTCP/IP Illustratedlt/titlegt
• lttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt

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Selection (cont.)

• Return the titles of all books published before
  1997
• /bib/book_at_year lt "1997"/title
• for bk in /bib/book
• where bk/_at_year lt "1997"
• return bk/title
• lttitlegtTCP/IP Illustratedlt/titlegt
• lttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt

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Selection (cont.)

• Return book with the title Data on the Web
• /bib/booktitle "Data on the Web"
• ltbook year"2000"gt
• lttitlegtData on the Weblt/titlegt
• ltauthorgtltlastgtAbiteboullt/lastgtltfirstgtSergelt/firstgt
  lt/authorgt
• ltauthorgtltlastgtBunemanlt/lastgtltfirstgtPeterlt/firstgtlt/
  authorgt
• ltauthorgtltlastgtSuciult/lastgtltfirstgtDanlt/firstgtlt/auth
  orgt
• ltpublishergtMorgan Kaufmann Publisherslt/publishergt
  
• ltpricegt 39.95lt/pricegt
• lt/bookgt

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Selection (cont.)

• Return the price of the book Data on the Web
• /bib/booktitle "Data on the Web"/price
• ltpricegt 39.95lt/pricegt
• How would you return the book with a price of
  39.95?

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Selection (cont.)

• Return the book with a price of 39.95
• for bk in /bib/book
• where bk/price " 39.95"
• return bk
• ltbook year"2000"gt
• lttitlegtData on the Weblt/titlegt
• ltauthorgtltlastgtAbiteboullt/lastgtltfirstgtSergelt/firstgt
  lt/authorgt
• ltauthorgtltlastgtBunemanlt/lastgtltfirstgtPeterlt/firstgtlt/
  authorgt
• ltauthorgtltlastgtSuciult/lastgtltfirstgtDanlt/firstgtlt/auth
  orgt
• ltpublishergtMorgan Kaufmann Publisherslt/publishergt
  
• ltpricegt 39.95lt/pricegt
• lt/bookgt

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Construction

• Return year and title of all books published
  before 1997
• for bk in /bib/book
• where bk/_at_year lt "1997"
• return ltbookgt bk/_at_year, bk/title lt/bookgt
• ltbook year"1994"gt
• lttitlegtTCP/IP Illustratedlt/titlegt
• lt/bookgt
• ltbook year"1992"gt
• lttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt
• lt/bookgt

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Grouping

• Return titles for each author
• for author in distinct(/bib/book/author/last)
  return
• ltauthor name author/text() gt
• /bib/bookauthor/last author/title
• lt/authorgt
• ltauthor name"Stevens"gt
• lttitlegtTCP/IP Illustratedlt/titlegt
• lttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt
• lt/authorgt
• ltauthor name"Abiteboul"gt
• lttitlegtData on the Weblt/titlegt
• lt/authorgt

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Join

• Return the books that cost more at amazon than
  fatbrain
• Let amazon document(http//www.amazon.com/book
  s.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 gt fat/price
• Return ltbookgt am/title, am/price, fat/price
  ltbookgt

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Example Query 1

• ltbibgt
• for b in /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
• What does this do?

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Result Query 1

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

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Example Query 2

• ltresultsgt
• for b in document("http//www.bn.com/bib.xml")/
  bib/book,
• t in b/title,
• a in b/author
• return
• ltresultgt
• t
• a
• lt/resultgt
• lt/resultsgt

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Result Query 2

• ltresultsgt
• ltresultgtlttitlegtTCP/IP Illustratedlt/titlegt
• ltlastgtStevens lt/lastgt
• lt/resultgt
• ltresultgtlttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt
• ltlastgtStevenslt/lastgt
• lt/resultgt
• ltresultgtlttitlegtData on the Weblt/titlegt
• ltlastgtAbiteboullt/lastgt
• lt/resultgt
• ltresultgt lttitlegtData on the Weblt/titlegt
• ltlastgtBunemanlt/lastgt
• lt/resultgt
• ltresultgtlttitlegtData on the Weblt/titlegt
• ltlastgtSuciult/lastgt
• lt/resultgt
• lt/resultsgt

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Example Query 3

• ltbooks-with-pricesgt
• for b in document("http//www.bn.com/bib.xml"
  )//book,
• a in document("http//www.amazon.com/revi
  ews.xml")//entry
• where b/title a/title
• return
• ltbook-with-pricesgt
• b/title
• ltprice-amazongt a/price/text()
  lt/price-amazongt
• ltprice-bngt b/price/text()
  lt/price-bngt
• lt/book-with-pricesgt
• lt/books-with-pricesgt

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Result Query 3

• ltbooks-with-pricesgt
• ltbook-with-pricesgt
• lttitlegtTCP/IP Illustratedlt/titlegt
• ltprice-amazongt65.95lt/price-amazongt
• ltprice-bngt 65.95lt/price-bngt
• lt/book-with-pricesgt
• ltbook-with-pricesgt
• lttitlegtAdvanced Programming in the Unix
  environmentlt/titlegt
• ltprice-amazongt65.95lt/price-amazongt
• ltprice-bngt65.95lt/price-bngt
• lt/book-with-pricesgt
• ltbook-with-pricesgt
• lttitlegtData on the Web lt/titlegt
• ltprice-amazongt34.95lt/price-amazongt
• ltprice-bngt 39.95lt/price-bngt
• lt/book-with-pricesgt
• lt/books-with-pricesgt

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Example Query 4

• 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

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Example Result 4

• 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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Impact of XML on Integration

• If and when all sources accept Xqueries and
  exchange data in XML format, then
• Mediator can accept user queries in Xquery
• Access sources using Xquery
• Get data back in XML format
• Merge results and send to user in XML format
• How about now?
• Sources can use XML adapters (middle-ware)

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Is XML standardization a magical solution for
Integration?

• If all WEB sources standardize into XML format
• Source access (wrapper generation issues) become
  easier to manage
• BUT all other problems remain
• Still need to relate source (XML)schemas to
  mediator (XML)schema
• Still need to reason about source overlap, source
  access limitations etc.
• Still need to manage execution in the presence of
  source/network uncertainities

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Semantic Web

• The LAV/GAV approaches assume that some human
  expert will do the actual schema mapping
• The semantic-web initiative attempts to
  automate schema mapping
• Idea Allow pages to write logical axioms
  relating their vocabulary (tags) to other
  external tags
• Support automatic inference of relations between
  source and mediator schema using these rules
• DAMLOIL

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Data Model
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Which will have XML Syntax
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Document Type Definition DTD

• part of the original XML specification
• an XML document may have a DTD
• terminology for XML
• well-formed if tags are correctly closed
• valid if it has a DTD and conforms to it
• validation is useful in data exchange

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Notice that DTD is not In XML syntax ?
71
Two ways to specify a DTD

• External DTD
• Internal

lt?xml version"1.0"?gt lt!DOCTYPE greeting SYSTEM
"hello.dtd"gt ltgreetinggtHello, world!lt/greetinggt
lt?xml version"1.0" encoding"UTF-8" ?gt lt!DOCTYPE
greeting lt!ELEMENT greeting
(PCDATA)gt gt ltgreetinggtHello,
world!lt/greetinggt
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DTDs as Grammars
lt!DOCTYPE paper lt!ELEMENT paper
(section)gt lt!ELEMENT section ((title,section)
text)gt lt!ELEMENT title (PCDATA)gt
lt!ELEMENT text (PCDATA)gt gt
ltpapergt ltsectiongt lttextgt lt/textgt lt/sectiongt
ltsectiongt lttitlegt lt/titlegt ltsectiongt
lt/sectiongt
ltsectiongt lt/sectiongt
lt/sectiongt lt/papergt
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Shortcomings of DTDs

• Useful for documents, but not so good for data
• No support for structural re-use
• Object-oriented-like structures arent supported
• No support for data types
• Cant do data validation
• Can have a single key item (ID), but
• No support for multi-attribute keys
• No support for foreign keys (references to other
  keys)
• No constraints on IDREFs (reference only a
  Section)

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XML Schema

• In XML format
• Includes primitive data types (integers, strings,
  dates, etc.)
• Supports value-based constraints (integers gt 100)
• User-definable structured types
• Inheritance (extension or restriction)
• Foreign keys
• Element-type reference constraints

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XML Schemas
Pre-specified tags

• ltelementType namepapergt
• ltsequencegt
• ltelementTypeRef nametitle/gt
• ltelementTypeRef nameauthor
  minOccurs0/gt
• ltelementTypeRef nameyear/gt
• ltchoicegt ltelementTypeRef
  namejournal/gt
• ltelementTypeRef
  nameconference/gt
• lt/choicegt
• lt/sequencegt
• lt/elementTypegt

How many different RDBMS Schemas are needed here?
DTD lt!ELEMENT paper (title,author,year,
(journalconference))gt
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Sample XML Schema

• ltschema version1.0 xmlnshttp//www.w3.org/199
  9/XMLSchemagt
• ltelement nameauthor typestring /gt
• ltelement namedate type date /gt
• ltelement nameabstractgt
• lttypegt
• lt/typegt
• lt/elementgt
• ltelement namepapergt
• lttypegt
• ltattribute namekeywords typestring/gt
• ltelement refauthor minOccurs0
  maxOccurs /gt
• ltelement refdate /gt
• ltelement refabstract minOccurs0
  maxOccurs1 /gt
• ltelement refbody /gt
• lt/typegt
• lt/elementgt
• lt/schemagt

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Subtyping in XML Schema

• ltschema version1.0 xmlnshttp//www.w3.org/199
  9/XMLSchemagt
• lttype namepersongt
• ltattribute namessngt
• ltelement nametitle minOccurs0
  maxOccurs1 /gt
• ltelement namesurname /gt
• ltelement nameforename minOccurs0
  maxOccurs /gt
• lt/typegt
• lttype nameextended sourceperson
  derivedByextensiongt
• ltelement namegeneration minOccurs0 /gt
• lt/typegt
• lttype namenotitle sourceperson
  derivedByrestrictiongt
• ltelement nametitle maxOccurs0 /gt
• lt/typegt
• ltkey namepersonKeygt
• ltselectorgt.//person_at_ssnlt/selectorgt
• ltfieldgt_at_ssnlt/fieldgt
• lt/keygt
• lt/schemagt

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DTDs as Schemas

• Not so well suited
• impose unwanted constraints on order
  lt!ELEMENT person (name,phone)gt
• references cannot be constrained
• can be too vague
• lt!ELEMENT person ((namephoneemail))gt
• Union of schemas..?

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XML Schemas

• recent proposal
• 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

83
Although DB folks have several beefs
Give me the names of people who are Listed either
as editor or author of a book
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Differences between XML and SSD

• Pure SSD uses edge-labeled graphs as data model
• XML is ordered, ssd is not
• XML can mix text and elements
• lttalkgt Making Java easier to type and easier
  to type
• ltspeakergt Phil Wadler lt/speakergt
• lt/talkgt
• XML has lots of other stuff entities, processing
  instructions, comments

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XML vs. standard semi-structured data models

• ltperson ido123gt
• ltnamegt Alan lt/namegt
• ltagegt 42 lt/agegt
• ltemailgt ab_at_com lt/emailgt
• lt/persongt

• person o123
• name Alan,
• age 42,
• email ab_at_com

Node labeling
Edge labeling
similar on trees, different on graphs
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XML seen from (R)DBMS world

• RDBMS may want to publish data in XML provide
  an XML view of their data
• Tagging the output
• Support XML-based querying (which are then
  converted to SQL querying)
• Single XML-QL query may correspond to a set of
  SQL queries
• E.g. Schema queries
• SilkRoute, Xperanto systems
• Support XML-based updating
• Tukwila
• RDBMS can be used to provide an efficient storage
  for XML files
• Efficient indexing/retrieval of path expressions

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Other Important XML Standards

• XSL/XSLT
• presentation and transformation standards
• RDF
• resource description framework (meta-info such as
  ratings, categorizations, etc.)
• Xpath/Xpointer/Xlink
• standard for linking to documents and elements
  within
• Namespaces
• for resolving name clashes
• DOM
• Document Object Model for manipulating XML
  documents
• SAX
• Simple API for XML parsing

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RDF

• http//www.w3.org/TR/REC-rdf-syntax (2/99)
• purpose metadata for Web
• help search engines
• syntax in XML
• semantics edge-labeled graphs

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RDF Metadata standard

• ltrdfDescription aboutwww.mypage.comgt
• ltaboutgt birds, butterflies, snakes
  lt/aboutgt
• ltauthorgt ltrdfDescriptiongt
• ltfirstnamegt John
  lt/firstnamegt
• ltlastnamegt Smith
  lt/lastnamegt
• lt/rdfDescriptiongt
• lt/authorgt
• lt/rdfDescriptiongt

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More RDF Examples
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RDF Terminology
statement
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More RDF Containers

• bag, sequence, alternative
• ltrdfDescriptiongt ltagt ltrdfBaggt
• 
  ltrdfligt s1 lt/rdfligt
• 
  ltrdfligt s2 lt/rdfligt
• lt/rdfBaggt
• lt/agt
• lt/rdfDescriptiongt

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RDF Containers (contd)
a
rdftype
rdf_2
rdf_1
Bag
s1
s2
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More RDF Higher Order Statements

• the author of www.thispage.com says the topic
  of www.thatpage.com is environment

RDF uses reification
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XML Parsers

• traditional return data structure (DOM?)
• event based SAX (Simple API for XML)
• http//www.megginson.com/SAX
• write handler for start tag and for end tag

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Need for Ontology standardization
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XML Data Model

• does not exists
• Document Object Model (DOM)
• http//www.w3.org/TR/REC-DOM-Level-1 (10/98)
• class hierarchy (node, element, attribute,)
• objects have behavior
• defines API to inspect/modify the document

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Start of 4/9 lecture
108
Querying XML
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XML Data Model (Graph)
Think of the labels as names of binary relations.

• Issues
• distinguish between attributes and
  sub-elements?
• Should we conserve order?

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Need for XML querying
human-readable documents to retrieve individual
documents, to provide dynamic indexes, to perform
context-sensitive searching, and to generate new
documents. data-oriented documents to query
(virtual) XML representations of databases, to
transform data into new XML representations, and
to integrate data from multiple heterogeneous
data sources. mixed-model documents to perform
queries on documents with embedded data, such as
catalogs, patient health records, employment
records, or business analysis documents.
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Querying XML

• Requirements
• Query a graph, not a relation.
• The result should be a graph (representing an XML
  document), not a relation.
• No schema.
• We may not know much about the data, so we need
  to navigate the XML.

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W3C requirements

• The W3C Query Working Group has identified many
  technical requirements
• at least one XML syntax at least one
  human-readable syntax.
• must be declarative
• must be protocol independent
• must respect XML data model
• must be namespace aware
• must coordinate with XML Schema
• must work even if schemas are unavailable
• must support simple and complex datatypes
• must support universal and existential
  quantifiers
• must support operations on hierarchy and sequence
  of document structures
• must combine information from multiple documents
  
• must support aggregation
• must be able to transform and to create XML
  structures
• must be able to traverse ID references.

113
Query Languages

• XML-QL Invented by DB folks
• XML-QL is relational-complete (allows Joins)
• also supports path expressions
• Can extract as well as transform data into
  different formats (like XSL)
• XML-QL is not in XML syntax
• XSL can also be seen as a query language
• Can transform data

114
XML-QL data model

• XML-QL works on an abstraction, called an XML
  graph, of the concrete XML document
• comments and processing instructions are ignored
  
• the relative order of elements is ignored
• every node has an ID (autogenerated, if
  necessary)
• all leaves are character data.
• XML graphs are obtained from XML documents but
  are also generated by queries.
• A graph is mapped back into an XML document by
  choosing arbitrary orderings of element
  sequences.
• This abstraction is very similar to that from
  tables to relations disregard the order of
  tuples and attributes.

115
Extracting Data by Query

• Matching data using elements patterns.
• WHERE ltbookgt
• ltpublishergtltnamegtAddison-Wesleylt/gtlt/gt
• lttitlegt t lt/gt
• ltauthorgt a lt/gt
• lt/bookgt IN www.a.b.c/bib.xml
• CONSTRUCT a

where clause only specifies What must be in
the pattern --pattern can have other stuff
besides what is listed in where
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Constructing XML Data

• WHERE ltbookgt
• ltpublishergtltnamegtAddison-Wesleylt/gtlt/gt
• lttitlegt t lt/gt
• ltauthorgt a lt/gt
• lt/gt IN www.a.b.c/bib.xml
• CONSTRUCT ltresultgt
• ltauthorgt a lt/gt
• lttitlegt tlt/gt
• lt/gt

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Grouping with Nested Queries

• WHERE ltbookgt
• lttitlegt t lt/gt,
• ltpublishergtltnamegtAddison-Wesleylt/gtlt/gt
• lt/gt CONTENT_AS p IN www.a.b.c/bib.xml
• CONSTRUCT ltresultgt
• lttitregt t lt/gt
• WHERE ltauthorgt a lt/gt IN p
• CONSTRUCT ltauteurgt alt/gt
• lt/gt

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Joining Elements by Value(also integration)
Multiple queries That share values

• WHERE ltarticlegt ltauthorgt
• ltfirstnamegt f lt/gt ltlastnamegt l lt/gt
• lt/gt lt/gt ELEMENT_AS e IN www.a.b.c/artbib.xm
  l
• ltbook yearygt ltauthorgt
• ltfirstnamegt f lt/gt ltlastnamegt l lt/gt
• lt/gt lt/gt IN www.a.b.c/bookbib.xml , y gt 1995
• CONSTRUCT e

Find all articles whose writers also published a
book after 1995.
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Tag variables (schema queries)
  WHERE ltpgt            lttitlegt t lt/titlegt
           ltyeargt 1995 lt/gt            ltegt Smith
lt/gt          lt/gt IN "www.a.b.c/bib.xml",        
e IN author, editor   CONSTRUCT ltpgt
               lttitlegt t lt/titlegt               
ltegt Smith lt/gt              lt/gt

• p matches book and article.
• e matches author and editor.
• this saves us from writing four queries.
• This finds all publications in 1995 where Smith
  is either author or editor

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Path Expressions
  WHERE ltpartgt ltnamegt r lt/gt ltbrandgt Ford lt/gt
lt/gt IN "www.a.b.c/parts.xml
"    CONSTRUCT ltresultgt r lt/gt
Matches any sequence of nodes all of which are
labeled part (can substitute for part in the
above)
  WHERE ltpart.(subpartcomponent.piece)gtrlt/gt IN
"www.a.b.c/parts.xml"    CONSTRUCT ltresultgt rlt/gt
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Due 30th April
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