This document provides an overview of XPath, an XML query language. It discusses what XPath is, the different types of nodes it can select, and relationship between nodes. It also covers XPath axes that define relationships between nodes, predicates that allow testing nodes, and standard functions like count(), position(), and last(). Examples are provided to demonstrate selecting elements and attributes in an XML document using XPath node tests, axes, predicates and functions. Exercises at the end provide practice with querying XML to retrieve title and price of books, find average textbook price, and return titles of textbooks on XML.

1. Querying XML with XPATH
Basics and understanding
Malintha Adikari
Software Engineer

2. What is Xpath
● XPath is an XML query language.
● XPath is a building block for other XML
● XPath is a syntax for defining parts of an XML document
● XPath uses path expressions to navigate in XML
documents
● XPath contains a library of standard functions
● XPath is a major element in XSLT

3. Xpath is All About
● Nodes
● element
● attribute
● text
● namespace
● processing-instruction
● comment
● document (root) nodes

4. Relationship Of Nodes
<bookstore>
<book>
<title>Harry Potter</title>
<author>J K. Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>
</bookstore>

5. Relationship Of Nodes
● Parent: Each element and attribute
has one parent.
● Children: Element nodes may have
zero, one or more children.
● Siblings: Nodes that have the same
parent.
● Ancestors: A node's parent, parent's
parent, etc.
● Descendants: A node's children,
children's children, etc.
</bookstore>
<book>
<title>Harry Potter</title>
<author>J K.
Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>
</bookstore>

6. Basics -Slashes (/)
● A path that begins with a / represents an absolute path, starting from the top
of the document
○ Example: /email/message/header/from
○ Note that even an absolute path can select more than one element
○ A slash by itself means “the whole document”
● A path that does not begin with a / represents a path starting from the current
element
○ Example: header/from
● A path that begins with // can start from anywhere in the document
○ Example: //header/from selects every element from that is a child of an element header
○ This can be expensive, since it involves searching the entire document

7. Basics -Brackets and last()
● A number in brackets selects a particular matching child
○ Example: /library/book[1] selects the first book of the library
○ Example: //chapter/section[2] selects the second section of every chapter in the XML document
○ Example: //book/chapter[1]/section[2]
○ Only matching elements are counted; for example, if a book has both sections and exercises,
the latter are ignored when counting sections
● The function last() in brackets selects the last matching child
○ Example: /library/book/chapter[last()]
● You can even do simple arithmetic
○ Example: /library/book/chapter[last()-1]

8. Basics -Wild cards
● A star, or asterisk, is a "wild card“ -- it means "all the elements at
this level"
○ Example: /library/book/chapter/* selects every child of every
chapter of every book in the library
○ Example: //book/* selects every child of every book
(chapters, tableOfContents, index, etc.)
○ Example: /*/*/*/paragraph selects every paragraph that has
exactly three ancestors
○ Example: //* selects every element in the entire document

9. Get This XML
<?xml version="1.0" encoding="ISO-8859-1"?>
<bookstore>
<book isbn= “111111” cat=“fiction”>
<title lang=“chn”>Harry Potter</title>
<price unit=“us”>79.99</price>
</book>
<book isbn=“222222” cat=“textbook”>
<title lang=“eng”>Learning XML</title>
<price unit=“us”>69.95</price>
</book>
<book isbn "333333" cat "textbook">
<title lang="eng">Intro. to Databases</title>
<price unit="usd">39.00</price>
</book>
</bookstore>

10. Selecting element of XML- Basics

11. Node Selection
<?xml version="1.0" encoding="ISO-8859-
1"?>
<bookstore>
<book isbn= <book isbn= 111111 cat=
fiction > “111111” cat=“fiction”>
<title lang=“chn”>Harry
Potter</title>
<price unit=“us”>79.99</price>
</book>
<book isbn=“222222” cat=“textbook”>
<title lang=“eng”>Learning
XML</title>
<price unit=“us”>69.95</price>
</book>
<book isbn "333333" cat "textbook">
<title lang="eng">Intro. to
Databases</title>
<price unit="usd">39.00</price>
</book>
</bookstore>

12. Node Selection Solutions

13. Xpath Axes
An axis defines a node-set relative to the current node.
• self‐‐the context node itself
• child‐‐the children of the context node
• descendant‐-all descendants (children+)
• parent‐‐the parent (empty if at the root)
• ancestor‐‐all ancestors from the parent to the root
• descendant descendant‐or‐self ‐‐the union of descendant descendant and self
• ancestor‐or‐self ‐‐the union of ancestor and self
• following‐sibling‐‐siblings to the right
• preceding‐sibling‐‐siblings to the left
• following‐‐all following nodes in the document, excluding descendants
• attribute‐‐the attributes of the context node

14. Xpath Axes sample
<?xml version="1.0" encoding="ISO-8859-
1"?>
<bookstore>
<book isbn= “111111 cat= “fiction”>
<title lang=“chn”>Harry
Potter</title>
<price unit=“us”>79.99</price>
</book>
<book isbn=“222222” cat=“textbook”>
<title lang=“eng”>Learning
XML</title>
<price unit=“us”>69.95</price>
</book>
<book isbn "333333" cat "textbook">
<title lang="eng">Intro. to
Databases</title>
<price unit="usd">39.00</price>
</book>
</bookstore>

15. Xpath Operators

16. Predicates
[position() op #],[last()]
–op: =, !=, <, >, <=, >=
–test position among siblings
•[attribute::name [attribute::name op “value ]"
–op: =, !=, <, >, <=, >=
–test equality equality of an attribute attribute
•[axis:nodeSelector]
–test pattern

17. Predicates Samples
<?xml version="1.0" encoding="ISO-8859-
1"?>
<bookstore>
<book isbn=“111111” cat=“fiction”>
<title lang=“chn”>Harry
Potter</title>
<price unit=“us”>79.99</price>
</book>
<book isbn=“222222” cat=“textbook”>
<title lang=“eng”>Learning
XML</title>
<price unit=“us”>69.95</price>
</book>
<book isbn "333333" cat "textbook">
<title lang="eng">Intro. to
Databases</title>
<price unit="usd">39.00</price>
</book>
</bookstore>

18. XPath Standard Functions
● number position()
Return the position of the context node among the list of nodes that
are currently being evaluated.
● count()
Return the number of nodes in the argument node-set
number count(node-set)
● number last()
Return the index of the last node in the list that is currently being
evaluated
http://www.w3schools.com/xpath/xpath_functions.asp

19. XPath: exercise
1. Find the title and price of non fiction
books with a price more than 50 USD.
2. Find average price of textbooks.
3. Find the titles of textbooks on XML.
<?xml version="1.0" encoding="ISO-8859-
1"?>
<bookstore>
<book isbn=“111111” cat=“fiction”>
<title lang=“chn”>Harry
Potter</title>
<price unit=“us”>79.99</price>
</book>
<book isbn=“222222” cat=“textbook”>
<title lang=“eng”>Learning
XML</title>
<price unit=“us”>69.95</price>
</book>
<book isbn "333333" cat "textbook">
<title lang="eng">Intro. to
Databases</title>
<price unit="usd">39.00</price>
</book>
</bookstore>

20. Answers
1. Find the title and price of non “COOKING” books with a price more than 25
USD.
/bookstore/book[attribute::category!="COOKING" and price > 25]/title/text() | /bookstore/book
[attribute::category!="COOKING" and price > 25]/price/text())
2. Find average price of “WEB” books.
sum(//book[attribute::category="WEB"]/price/text()) div count(//book[attribute::category="WEB"])
3. Find the titles of textbooks on XML.
//book[@category="textbook" and contains(title,"XML")]/title/text()

21. More Exercises
● Setup Eclipse with plugins for xml, XSD and XSLT
● Try Xpath samples at
http://www.zvon.org/xxl/XPathTutorial/General/examples.html
● Take sample xml and try out Xpath functions
http://www.w3schools.com/xpath/xpath_functions.asp
● Take automation.xml from following svn location and try to implement xsd for
that. We will discuss this in next session
https://svn.wso2.org/repos/wso2/carbon/platform/branches/turing/platform-
integration/test-automation-framework-2/org.wso2.carbon.automation.engine/4.3.0
/src/main/resources/automation.xml

22. Questions?

23. Contact us !