CSE3201/CSE4500 Information Retrieval Systems XPath and XSLT CSE3201/CSE4500 Information Retrieval Systems

Manipulating XML Documents parser data Applications

What is XSL Extensible Stylesheet Language Developed by W3C XSL Working Group Motivation: to handle the manipulation and presentation of XML documents Consists of: XSLT and XSL-FO

XSL Presentation document Transformation process XML document Stylesheet processor XML document XSL document Presentation document Transformation process

Transformation Tools XPath XSL(Extensible Stylesheet Languages) XSLT(XSL Transformation) XSL-FO(XSL Formatting Object)

Transformation Process

XSLT Processing Type of processings: Output Uses Change of vocabulary Reorder data elements Combine data elements Filter and exclude data elements Output Other XML vocabularies or fragments Non-XML formats Uses Display and printing Transformation of data

XPath A locator for items in XML document. XPath expression gives direction of navigation in XML document. Assume an XML document as a “tree” Any part of a document, eg element, attribute, is considered as a “node” Current version XPATH 1.0

XPath Syntax (full form): Axis Node test Predicate: describing the relationship between nodes, eg child, parents, etc. Node test condition for selecting nodes. Predicate: further condition refinement of the set of nodes resulted from the node test.

XPath Axes context node Ancestor Parent/ancestor sibling node child/descendant descendant attribute context node

Node Test A node test identifies nodes in the document that meet the criteria of the test. The simplest type of test is nodes that match an element name. Example: child::book => to find any child element with the name “book”. child::author

Predicate Predicate further refine or filter the node-set produced by the node test. Example: Find the third book in the list child::book[position( )=3] Find all the books that has <isbn> element child::book[isbn]

Abbreviations Formal Short Description child::book book Select all children of the context node that has <book> element nodes. child::* * Select all element nodes of the context node. self::node() . Select the context node. parent::node() .. Select the parent of the context node. child::book[position()=1] Book[1] Select the first child element that has <book> element. attribute::* @* select all the attributes of the context node attribute::number @number Find the number of attributes in the context node.

Location Path Uses “/” to build path, eg Document Root /name/first “John” <middle> “Little” <last> “Howard”

Relative vs Absolute Path full path needs to be included, starting from the root node. eg: /name/first Relative Path path is declared starting from the current context node. eg: assume our current context is “name”, the XPath expression for the node first => first

Recursive Decent Operator Locating nodes based on their names, regardless of where their positions in the document. Uses “//” Example: //first Select any <first> element in the document (regardless how far down the tree). Decrease the performance of the stylesheet. The entire document must be searched by the XSLT parser.

Filtering Nodes It is done using XPath’s predicate. the “[ ]” symbol. Using element as a filter: book[price] matches any <book> element that has a <price> child element. Using attribute as a filter: book[@id] matches any <book> element that has an id attribute.

XPath Expression Some possible operators to build an XPath Expression: and Logical AND or Logical OR not() logical negation = Equal != Not equal < Less than <= Less than equal > Greater than >= Greater than equal | Union

XPath Expression - Examples <xsl:template match="/"> <xsl:if test=“not(position()=last())”>

Usage of XPath in XSLT XSLT uses XPath expression to: Match node sets in order to execute templates. Evaluate node sets to control execution of conditional XSLT elements. Select node sets to change current context and direct the flow of the execution through the source document. Select node sets to obtain an output value Professional XML, page 379.

XPath Function XPath functions can be used to: manipulate node set eg: count, last, name, position manipulate string eg: concat, substring, contains test boolean value eg: language, false, true perform numeric operations eg: ceiling, floor, number, round, sum XSLT specific manipulation eg: current

XPath Function - Examples <xsl:if test=“not(position()=last())”> substring(‘abcde’,2,3) => returns ‘bcd’

Structure of Stylesheet An XSLT stylesheet is an XML document. Root element is stylesheet element <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> … </xsl:stylesheet> Consists of a set of rules. Rules are made up of patterns and templates.

Attaching an XSL to an XML doc <?xml-stylesheet type="text/xsl" href="books.xsl"?> href refers to the filename of the XSL document.

Example of a Stylesheet <bookshop> <book> <title> Harry Potter and the Sorcerer stone </title> <author> <initials>J.K</initials> <surname> Rowling</surname> </author> <price value=“$16.95”></price> </book> … </bookshop> <?xml version="1.0"?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> <xsl:output method="html"/> <xsl:template match="/"> <html> <body> <h1>Book</h1> <xsl:value-of select="bookshop/book/title"/> </body> </html> </xsl:template> </xsl:stylesheet>

Selecting Output Type Possible outputs: Syntax: XML, HTML, Text <xsl-output method=“xml”/> <xsl-output method=“text”/> <xsl-output method=“html”/>

Templates To create a template, we need: To declare the location in the source tree where the template will be applied. Rules of matching to be applied. can be another template The location is declared using the XPath expression.

Using Templates Templates are called using the <xsl:apply template>. <xsl:apply-templates   select = node-set-expression>  </xsl:apply-templates> The “select” attribute is optional. Without the “select” attribute, the XSL processor will apply the templates to all the child elements of the current context node.

Template Examples <?xml version="1.0"?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> <xsl:output method="html"/> <xsl:template match="/bookshop/book"> <html> <body> <h1>Book</h1> <xsl:apply-templates/> </body> </html> </xsl:template> </xsl:stylesheet>

Selecting Templates <?xml version="1.0"?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> <xsl:output method="html"/> <xsl:template match="/"> <html> <body> <h1>Monash Bookshop</h1> <xsl:apply-templates select="bookshop/book"/> </body> </html> </xsl:template>

Selecting Templates- cont’d <xsl:template match="book" > <xsl:apply-templates select="author"/> </xsl:template> <xsl:template match="author"> <h2>Author</h2> <xsl:value-of select="."/> </xsl:stylesheet>

Getting the Value of a Node xsl:value-of select=XPath expression Example: <xsl:template match="bookshop/book"> <p><xsl:value-of select="title"/></p> </xsl:template>

Conditional Test xsl:if Example: there is no “else” statement. takes one attribute, test, which is an XPath expression. if it evaluates true, the body of the element is executed Example: <xsl:if test=“@id”> …</xsl:if>

Iteration <xsl:for-each> <xsl:template match="/"> <html> <body> <h1>Book</h1> <xsl:for-each select="/bookshop/book"> <p> <xsl:value-of select="title"/> </p> </xsl:for-each> </body> </html> </xsl:template> <html> <body> <h1>Book</h1> <p> Harry Potter and the Sorcerer Stone</p> <p> Harry Potter</p> </body> </html>

Making Copies xsl:copy It does not copy any child nodes that the context node may have. xsl:copy-of copies all <xsl:template match="/bookshop"> <html> <body> <h1>Book</h1> <xsl:copy/> </body> </html> </xsl:template> <html> <body> <h1>Book</h1> <bookshop></bookshop> </body> </html>

Copy-of <?xml version="1.0"?> <xsl:stylesheet version = '1.0' xmlns:xsl='http://www.w3.org/1999/XSL/Transform'> <xsl:output method="xml"/> <xsl:template match="/"> <xsl:element name="Author_List"> <xsl:apply-templates/> </xsl:element> </xsl:template> <xsl:template match="bookshop/book"> <xsl:copy-of select="author"/> </xsl:stylesheet> <?xml version="1.0" encoding="utf-8"?> <Author_List> <author> <initials>JK</initials> <surname> Rowling</surname> </author> <initials>J</initials> </Author_List>