Querying XML with XPATH
Basics and understanding
Malintha Adikari
Software Engineer
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
Xpath is All About● Nodes ● element ● attribute● text● namespace● processing-instruction● comment● document (root) nodes
Relationship Of Nodes<bookstore>
<book> <title>Harry Potter</title> <author>J K. Rowling</author> <year>2005</year> <price>29.99</price>
</book> </bookstore>
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>
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
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]
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
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>
Selecting element of XML- Basics
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>
Node Selection Solutions
Xpath AxesAn 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
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>
Xpath Operators
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
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>
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-setnumber 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
XPath: exercise1. 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>
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()
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
Questions?
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