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More XML: semantics, DTDs, XPATH

More XML: semantics, DTDs, XPATH. February 18, 2004. attributes. name elements. person elements. XML Document. < data > < person id =“o555” > < name > Mary </ name > < address > < street > Maple </ street > < no > 345 </ no > < city > Seattle </ city > </ address > </ person >

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More XML: semantics, DTDs, XPATH

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  1. More XML: semantics, DTDs, XPATH February 18, 2004

  2. attributes name elements person elements XML Document • <data> • <person id=“o555”> • <name> Mary </name> • <address> • <street> Maple </street> • <no> 345 </no> • <city> Seattle </city> • </address> • </person> • <person> • <name> John </name> • <address> Thailand </address> • <phone> 23456 </phone> • <married/> • </person> • </data>

  3. XML Terminology • Elements • enclosed within tags: • <person> … </person> • nested within other elements: • <person> <address> … </address> </person> • can be empty • <married></married> abbreviated as <married/> • can have Attributes • <person id=“0005”> … </person> • XML document has as single ROOT element

  4. Buzzwords • What is XML? • W3C data exchange format • Hierarchical data model • Self-describing • Semi-structured

  5. Elementnode Attributenode person person id address address name phone name o555 Thai John Mary 23456 street no city Maple 345 Textnode Seattle XML as a Tree !! • <data> • <person id=“o555”> • <name> Mary </name> • <address> • <street> Maple </street> • <no> 345 </no> • <city> Seattle </city> • </address> • </person> • <person> • <name> John </name> • <address> Thailand </address> • <phone> 23456 </phone> • </person> • </data> data Minor Detail: Order matters !!!

  6. XML is self-describing • Schema elements become part of the data • In XML <persons>, <name>, <phone> are part of the data, and are repeated many times • Relational schema: persons(name,phone) defined separately for the data and is fixed • Consequence: XML is much more flexible

  7. <persons> <person> <name>John</name> <phone> 3634</phone> </person> <person> <name>Sue</name> <phone> 6343</phone> </person> <person> <name>Dick</name> <phone> 6363</phone> </person> </persons> persons XML: person person person phone name phone name phone name “John” 3634 “Sue” 6343 “Dick” 6363 Relational Data as XML person

  8. XML is semi-structured • Missing elements: • Could represent in a table with nulls <person> <name> John</name> <phone>1234</phone> </person> <person> <name>Joe</name> </person>  no phone !

  9. XML is semi-structured • Repeated elements • Impossible in tables: <person> <name> Mary</name> <phone>2345</phone> <phone>3456</phone> </person>  two phones ! ???

  10. XML is semi-structured • Elements with different types in different objects • Heterogeneous collections: • <persons> can contain both <person>s and <customer>s <person> <name> <first> John </first> <last> Smith </last> </name> <phone>1234</phone> </person>  structured name !

  11. Document Type Definition: DTD • an XML document may have a DTD • rules about the contents of elements • like a schema for an XML document • XML document: well-formed= if tags are correctly closed valid= if it has a DTD and conforms to it • validation is useful in data exchange • part of the original XML specification

  12. Root Element Element What’s in the element? Very Simple DTD <!DOCTYPE company [ <!ELEMENT company ((person|product)*)> <!ELEMENT person (ssn, name, office, phone?)> <!ELEMENT ssn (#PCDATA)> <!ELEMENT name (#PCDATA)> <!ELEMENT office (#PCDATA)> <!ELEMENT phone (#PCDATA)> <!ELEMENT product (pid, name, description?)> <!ELEMENT pid (#PCDATA)> <!ELEMENT description (#PCDATA)> ]>

  13. DTD: The Content Model • Content model: • Complex = a regular expression over other elements • Text-only = #PCDATA • Empty = EMPTY • Any = ANY • Mixed content = (#PCDATA | A | B | C)* <!ELEMENT tag (CONTENT)> contentmodel

  14. Very Simple DTD Example of valid XML document: <company> <person> <ssn> 123456789 </ssn> <name> John </name> <office> B432 </office> <phone> 1234 </phone> </person> <person> <ssn> 987654321 </ssn> <name> Jim </name> <office> B123 </office> </person> <product> ... </product> ... </company>

  15. DTD: Regular Expressions DTD XML sequence <!ELEMENT name (firstName, lastName)) <name> <firstName> . . . . . </firstName> <lastName> . . . . . </lastName> </name> optional <!ELEMENT name (firstName?, lastName)) <person> <name> . . . . . </name> <phone> . . . . . </phone> <phone> . . . . . </phone> <phone> . . . . . </phone> . . . . . . </person> Kleene star <!ELEMENT person (name, phone*)) alternation <!ELEMENT person (name, (phone|email))) lots of other features

  16. Querying XML Data • XPath = simple navigation through the tree • XQuery = the SQL of XML • XSLT = recursive traversal • will not discuss in class

  17. Sample Data for Queries <bib><book> <publisher> Addison-Wesley </publisher> <author> Serge Abiteboul </author> <author> <first-name> Rick </first-name> <last-name> Hull </last-name> </author> <author> Victor Vianu </author> <title> Foundations of Databases </title> <year> 1995 </year></book><bookprice=“55”> <publisher> Freeman </publisher> <author> Jeffrey D. Ullman </author> <title> Principles of Database and Knowledge Base Systems </title> <year> 1998 </year></book> </bib>

  18. bib Data Model for XPath The root The root element book book publisher author . . . . Addison-Wesley Serge Abiteboul

  19. XPath: Simple Expressions Result: <year> 1995 </year> <year> 1998 </year> Result: empty (there were no papers) /bib/book/year /bib/paper/year

  20. XPath: Restricted Kleene Closure //author Result:<author> Serge Abiteboul </author> <author> <first-name> Rick </first-name> <last-name> Hull </last-name> </author> <author> Victor Vianu </author> <author> Jeffrey D. Ullman </author> Result: <first-name> Rick </first-name> /bib//first-name

  21. Xpath: Text Nodes Result: Serge Abiteboul Jeffrey D. Ullman Rick Hull doesn’t appear because he has firstname, lastname Functions in XPath: • text() = matches the text value • node() = matches any node (= * or @* or text()) • name() = returns the name of the current tag /bib/book/author/text()

  22. Xpath: Wildcard Result: <first-name> Rick </first-name> <last-name> Hull </last-name> * Matches any element //author/*

  23. Xpath: Attribute Nodes Result: “55” @price means that price is an attribute /bib/book/@price

  24. Xpath: Predicates /bib/book/author[firstname] Result: <author> <first-name> Rick </first-name> <last-name> Hull </last-name> </author>

  25. Xpath: More Predicates Result: <lastname> … </lastname> <lastname> … </lastname> /bib/book/author[firstname][address[//zip][city]]/lastname

  26. Xpath: More Predicates /bib/book[@price < “60”] /bib/book[author/@age < “25”] /bib/book[author/text()]

  27. Xpath: Summary bib matches a bib element * matches any element / matches the root element /bib matches a bib element under root bib/paper matches a paper in bib bib//paper matches a paper in bib, at any depth //paper matches a paper at any depth paper|book matches a paper or a book @price matches a price attribute bib/book/@price matches price attribute in book, in bib bib/book/[@price<“55”]/author/lastname matches…

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