Tutorial –XPath, XQuery
Tutorial ? XPath, XQuery
CSCC43 - Introduction to Databases
CSCC43: Intro. to Databases
1
XPath Terminology
? Node
? document root, element, attribute, text, comment, ...
? Relationship
? parent, child, sibling, ancestor, descendent, ...
? Exercise: Identify nodes and relationships in following xml document
Harry Potter
79.99
Learning XML 69.95
document root does not correspond to anything
Intro. to Databases
in the document
39.00
CSCC43: Intro. to Databases
2
Node selector
Expression / node //
. .. @
Description Selects the document root node (absolute path) Selects the node (relative path) Selects all descendent nodes of the current node that match the selection Selects the current node Selects the parent of the current node Selects attribute nodes
CSCC43: Intro. to Databases
3
Node selector: exercise
Result Selects the document root node Selects the bookstore element node Selects all book element nodes Selects all price element nodes Selects all lang attribute nodes
Path Expression
? ?
? ?
? ?
? ?
?
?
././.
?
/bookstore//@lang/../..
?
./book/tilte/@lang
CSCC43: Intro. to Databases
4
Node selector : exercise sol
Result
Path Expression
Selects the document root node
/
/.
Selects the bookstore element node
/bookstore
./bookstore
Selects all book element nodes
/bookstore/book
//book
Selects all price element nodes
bookstore/book/price
//price
Selects all lang attribute nodes
//@lang
Selects the document root node
././.
Selects all the book element nodes
/bookstore//@lang/../..
Selects the empty set
./book/tilte/@lang
CSCC43: Intro. to Databases
5
Node selector: more exercise
Result Selects text nodes of all price element nodes Select all child nodes of book element nodes Select all comment nodes
Select all nodes except attribute nodes
Select all attribute nodes
?
?
Path Expression ?
?
? ? ? /bookstore/book/text() /bookstore/book/title/..//@*
CSCC43: Intro. to Databases
6
Node selector: more exercise sol
Result Selects text nodes of all price element nodes Select all child nodes of book element nodes Select all comment nodes
Select all nodes except attribute nodes
Select all attribute nodes
Selects empty set
Select all attribute nodes which are descendant of book element nodes
Path Expression //price/text()
/bookstore/book/*
//comment() //node() //@* /bookstore/book/text() /bookstore/book/title/..//@*
CSCC43: Intro. to Databases
7
XPath Syntax and Semantics
? Syntax
? locationStep1/locationStep2/...
? locationStep = axis::nodeSelector[predicate]
? Semantics
? Find all nodes specified by locationStep1
? Find all nodes specified by axis::nodeSelector ? Select only those that satisfy predicate
? For each such node N:
? Find all nodes specified by locationStep2 using N as the current node
? Take union
? For each node returned by locationStep2 do the same using locationStep3, ...
CSCC43: Intro. to Databases
8
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