Querring xml with xpath

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  • 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


    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

    Harry Potter J K. Rowling 2005 29.99

  • 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.

    Harry Potter J K.

    Rowling 2005 29.99

  • 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

    Harry Potter 79.99

    Learning XML 69.95

    Intro. to Databases39.00

  • Selecting element of XML- Basics

  • Node Selection

    Harry Potter


    Learning XML


    Intro. to Databases


  • Node Selection Solutions

  • Xpath AxesAn axis defines a node-set relative to the current node. selfthe context node itself

    childthe children of the context node

    descendant-all descendants (children+)

    parentthe parent (empty if at the root)

    ancestorall ancestors from the parent to the root

    descendant descendantorself the union of descendant descendant and self

    ancestororself the union of ancestor and self

    followingsiblingsiblings to the right

    precedingsiblingsiblings to the left

    followingall following nodes in the document, excluding descendants

    attributethe attributes of the context node

  • Xpath Axes sample


    Potter 79.99

    Learning XML


    Intro. to Databases


  • 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


    test pattern

  • Predicates Samples


    Potter 79.99

    Learning XML


    Intro. to Databases


  • XPath Standard Functions number position()

    Return the position of the context node among the list of nodes that are currently being evaluated.


    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



  • 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.

    Harry Potter


    Learning XML


    Intro. to Databases


  • 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


    Take sample xml and try out Xpath functions


    Take automation.xml from following svn location and try to implement xsd for

    that. We will discuss this in next session





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