1. Spring 20051 Part III: Introduction to XPath XML Path Language

2. 2 Example for XPath Queries Addison-Wesley Serge Abiteboul Rick Hull Victor Vianu Foundations of Databases 1995 Freeman Jeffrey D. Ullman Principles of Database and Knowledge Base Systems 1998

3. Spring 20053 Data Model for XPath bib book publisherauthor.. Addison-WesleySerge Abiteboul The root The root element Processing instruction Comment price=55

4. Spring 20054 XPath: Simple Expressions /bib/book/year Result: 1995 1998 /bib/paper/year Result: an empty set of nodes (there were no papers)

5. Spring 20055 XPath: Restricted Kleene Closure //author Result: Serge Abiteboul Rick Hull Victor Vianu Jeffrey D. Ullman /bib//first-name Result: Rick A set of 4 nodes

6. Spring 20056 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. Spring 20057 XPath: Wildcard //author/* Result: Rick Hull * Matches any element (but not text or attribute)

8. Spring 20058 XPath: Attribute Nodes /bib/book/@price Result: “55” @price means that price is an attribute @* Matches any attribute

9. Spring 20059 XPath: Qualifiers /bib/book/author[first-name] Result: Rick Hull [first-name] means that author has to have a first-name child element.

10. Spring 200510 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. Spring 200511 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. Spring 200512 XPath: Summary bibmatches a bib element *matches any element /matches the root element /bibmatches a bib element under root bib/papermatches a paper in bib bib//papermatches a paper in bib, at any depth

13. Spring 200513 XPath: Summary (cont.) //papermatches a paper at any depth paper|bookmatches a paper or a book @pricematches a price attribute bib/book/@pricematches price attribute in book, in bib bib/book[@price<55]/author/last-name matches?

14. Spring 200514 The Root 1 2 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 … ; they become siblings of bib element. This is advanced xmlogy

15. Spring 200515 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. Spring 200516 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. Spring 200517 Shorthand notation Short formLong form child:: @attribute::.self::node()..parent::node() ///descendant-or-self::node()/ [number][position() = number]

18. Spring 200518 Shorthand notation - Examples Short formLong form /bib/book/child::bib/child::book /bib/book/@price/child::bib/child::book/ attribute::price /.//title (equivalent to //title) /self::node()/descendant-or- self::node()/child::title //author/../descendant-or-self::node()/ child::author/parent::node()

19. Spring 200519 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 !