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Part III: Introduction to XPath

Part III: Introduction to XPath. XML Path Language. Example for XPath Queries. < bib > < book price =“55”> < publisher >Addison-Wesley</ publisher > < author >Serge Abiteboul</ author > < author >< first-name >Rick</ first-name >

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Part III: Introduction to XPath

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  1. Part III: Introduction to XPath XML Path Language

  2. Example for XPath Queries <bib> <bookprice=“55”> <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> <book> <publisher>Freeman</publisher> <author>Jeffrey D. Ullman</author> <title>Principles of Database and Knowledge Base Systems</title> <year>1998</year> </book> </bib>

  3. bib Data Model for XPath The root Processing instruction Comment The root element book book publisher author price=55 . . . . Addison-Wesley Serge Abiteboul

  4. XPath: Simple Expressions /bib/book/year Result: <year>1995</year> <year>1998</year> /bib/paper/year Result: an empty set of nodes (there were no papers)

  5. 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> /bib//first-name Result: <first-name>Rick</first-name> A set of 4 nodes

  6. XPath: Functions /bib/book/author/text() Result: Serge Abiteboul Victor Vianu Jeffrey D. Ullman Rick Hull doesn’t appear because he has no text node Some functions in XPath: • text() = matches text nodes and returns the text value • node() = matches any node (regardless of type) • name() = returns the name of the current tag

  7. XPath: Wildcard //author/* Result: <first-name>Rick</first-name> <last-name>Hull</last-name> * Matches any element (but not text or attribute)

  8. XPath: Attribute Nodes /bib/book/@price Result: “55” @price means that price is an attribute @* Matches any attribute

  9. XPath: Qualifiers /bib/book/author[first-name] Result: <author> <first-name>Rick</first-name> <last-name>Hull</last-name> </author> [first-name] means that author has to have a first-name child element.

  10. XPath: More Qualifiers /bib/book/author[first-name][address[zip][city]]/last-name Result: returns all the last names of all authors with a first name and an address which includes city and zip code. […][…] means that author satisfies both qualifiers.

  11. XPath: More Qualifiers /bib/book[@price < 60] /bib/book[author/first-name = “Rick”] /bib/book[author/text()] /bib/book[2] Boolean expressions Existential expression Positional expression

  12. 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

  13. XPath: Summary (cont.) • //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/last-namematches?

  14. The Root <?xml version="1.0"?> <bib> <paper>1</paper> <paper>2</paper> </bib> • bib is the “document element” • The “root” is above bib • /bib = returns the document element • / = returns the root • Why? Because we may have comments before and after <bib>…</bib>; they become siblings of bib element. • This is advanced xmlogy

  15. XPath: More details • We can navigate along 13 axes: ancestor ancestor-or-self attribute child descendant descendant-or-self following following-sibling namespace parent preceding preceding-sibling self

  16. XPath: More details • Examples: • child::author/child::last-name = author/last-name • child::author/descendant-or-self::node()/child::zip = author//zip • child::author/parent::node() = author/.. • child::author/attribute::age = author/@age • What does this mean ? • book/publisher/parent::*/author • /bib//address[ancestor::book]

  17. Shorthandnotation

  18. Shorthand notation - Examples

  19. XPath: Even more details • name() = the name of the current node • /bib//*[name()=”book”] same as /bib//book • What does this mean ? /bib/book/author[.=../following-sibling::*/author and not(.=../preceding-sibling::*/author)] • Navigation axis gives us more power !

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