about XML/Xquery/RDF

HTML vs. XML <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> -Schema info part of the data “Self-describing” -Good for data exchange (albeit baroque for storage)

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

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

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

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

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

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

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

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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

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

HTML describes presentation <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

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

More XML: Attributes <book price = “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

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

XML vs. Relational Data TEXT XML 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) TEXT Structured (relational) Data XML Less Structure More

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>

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

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

Querying XML Requirements: Candidates 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

Agenda: Xquery examples Information Integration 11/20 Agenda: Xquery examples Information Integration

Xquery Resources XQuery 1.0: An XML Query Language W3C Working Draft 20 December 2001 XML Query Use Cases 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

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]

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]

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 )>

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> </bib>

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

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?

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

Craig Knoblock University of Southern California Xquery Tutorial Craig Knoblock University of Southern California

References XQuery 1.0: An XML Query Language XML Query Use Cases W3C Working Draft 20 December 2001 XML Query Use Cases 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

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 )>

Data for www.bn.com/bib.xml <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> <price>65.95</price>

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> </bib>

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

Projection Return the names of all authors of books /bib/book/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>

Project (cont.) /bib/book/author = 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>Abiteboul</last><first>Serge</first></author> <author><last>Buneman</last><first>Peter</first></author> <author><last>Suciu</last><first>Dan</first></author>

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>

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>

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>

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?

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>

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>

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 name="Abiteboul"> <title>Data on the Web</title> …

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>

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?

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

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>

Result Query 2 <results> <result><title>TCP/IP Illustrated</title> <last>Stevens </last> </result> <result><title>Advanced Programming in the Unix environment</title> <last>Stevens</last> <result><title>Data on the Web</title> <last>Abiteboul</last> <result> <title>Data on the Web</title> <last>Buneman</last> <last>Suciu</last> </results>

Example Query 3 <books-with-prices> { for $b in document("http://www.bn.com/bib.xml")//book, $a in document("http://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>

Result Query 3 <books-with-prices> <book-with-prices> <title>TCP/IP Illustrated</title> <price-amazon>65.95</price-amazon> <price-bn> 65.95</price-bn> </book-with-prices> <title>Advanced Programming in the Unix environment</title> <price-bn>65.95</price-bn> <title>Data on the Web </title> <price-amazon>34.95</price-amazon> <price-bn> 39.95</price-bn> </books-with-prices>

Example Query 4 <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>

Example Result 4 <bib> <book year="1992"> <title>Advanced Programming in the Unix environment</title> </book> <book year="1994"> <title>TCP/IP Illustrated</title> </bib>

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)

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

“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 DAML+OIL