XSLT

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XSLT

• Reference
• www.cis.upenn.edu/matuszek/ cit597-2002/Lectures/
  xslt.ppt

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XSLT

• XSLT stands for Extensible Stylesheet Language
  Transformations
• XSLT is used to transform XML documents into
  other kinds of documents--usually, but not
  necessarily, XHTML
• XSLT uses two input files
• The XML document containing the actual data
• The XSL document containing both the framework
  in which to insert the data, and XSLT commands to
  do so

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Very simple example

• File data.xml
• type"text/xsl" href"render.xsl"?Howdy
  !
• File render.xsl
• version"1.0 xmlnsxsl"http//www.w3.or
  g/1999/XSL/Transform"
  match"/"
  
  
  

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The .xsl file

• An XSLT document has the .xsl extension
• The XSLT document begins with
• xmlnsxsl"http//www.w3.org/1999/
  XSL/Transform"
• Contains one or more templates, such as
• ...
• And ends with

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The .xsl file

• An XSLT style sheet contains "template rules"
  that define
• the criteria for selecting elements from the
  source tree
• providing instructions for restructuring the
  selected content to create the result tree
• Template rules are the key building blocks of
  XSLT transformations.
• There are two parts to a template rule a pattern
  and a template.
• The "pattern" (usually an element name) is then
  "matched" against elements in the source tree to
  determine which nodes to select for processing.
• The "template" provides instructions for
  processing the selected content.
• Each template rule constructs a result tree
  fragment of markup and content. An XSLT
  Transformation's result tree is created when all
  of the result tree fragments are combined in the
  order specified to form a completed whole.

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The .xsl file

• The xsltemplate element is used to encapsulate
  template rules. The value of its "match"
  attribute contains an XPath statement that is
  used as a "pattern" to select source elements for
  processing.
• A document's first template almost always has a
  "match" value of "/", which means "the document
  root."
• The "apply-templates" element signals to an XSLT
  processor to look for other template rules and
  apply them at that point in the style sheet's
  structure. The results of each rule combine to
  form the "result tree" of the completed
  transformation.

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Finding the message text

• The template says to
  select the entire file
• You can think of this as selecting the root node
  of the XML tree
• Inside this template,
• selects the
  message child
• Alternative Xpath expressions that would also
  work
• ./message
• /message/text() (text() is an XPath function)
• ./message/text()

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Putting it together

• The XSL was
  select"message"/
  
• The chooses the root
• The is written to the output
  file
• The contents of message is written to the output
  file
• The is written to the
  output file
• The resultant file looks like
  Howdy!

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How XSLT works

• The XML text document is read in and stored as a
  tree of nodes
• The template is used to
  select the entire tree
• The rules within the template are applied to the
  matching nodes, thus changing the structure of
  the XML tree
• If there are other templates, they must be called
  explicitly from the main template
• Unmatched parts of the XML tree are not changed
• After the template is applied, the tree is
  written out again as a text document

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Where XSLT can be used

• With an appropriate program, such as Xerces, XSLT
  can be used to read and write files
• A server can use XSLT to change XML files into
  HTML files before sending them to the client
• A modern browser can use XSLT to change XML into
  HTML on the client side
• This is what we will mostly be doing in this
  class
• Most users seldom update their browsers
• If you want everyone to see your pages, do any
  XSL processing on the server side
• Otherwise, think about what best fits your
  situation

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Modern browsers

• Internet Explorer 6 best supports XML
• Netscape 6 supports some of XML
• Internet Explorer 5.x supports an obsolete
  version of XML
• IE5 is not good enough for this course

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xslvalue-of

• 
  selects the contents of an element and adds it to
  the output stream
• The select attribute is required
• Notice that xslvalue-of is not a container,
  hence it needs to end with a slash
• Example (from an earlier slide)

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xslfor-each

• xslfor-each is a kind of loop statement
• The syntax is expression" Text to insert and rules to
  apply
• Example to select every book (//book) and make
  an unordered list (
  ) of their titles (title),
  use
  select"//book"
  • select"title"/
  
  
  
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  Filtering output
  • You can filter (restrict) output by adding a
    criterion to the select attributes value
    
    
    
    • select"title../author'Terry Pratchett'"/
      
  • This will select book titles by Terry Pratchett
  
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  Filter details
  • Here is the filter we just used select"title../author'Terry Pratchett'/
  • author is a sibling of title, so from title we
    have to go up to its parent, book, then back down
    to author
  • This filter requires a quote within a quote, so
    we need both single quotes and double quotes
  • Legal filter operators are !
    lt gt
  • Numbers should be quoted, but apparently dont
    have to be
  
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  But it doesnt work right!
  • Heres what we did select"//book"
  • 
    erry Pratchett'"/
  • This will output
  • and
  for every book,
  so we will get empty bullets for authors other
  than Terry Pratchett
  • There is no obvious way to solve this with just
    xslvalue-of
  
  17
  xslif
  • xslif allows us to include content if a given
    condition (in the test attribute) is true
  • Example
    
    
  • 
    
  • This does work correctly!
  
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  xslchoose
  • The xslchoose ... xslwhen ... xslotherwise
    construct is XMLs equivalent of Javas switch
    ... case ... default statement
  • The syntax is test"some condition" ... some code
    ...
    ... some code ... choose
  
  xslchoose is often used within an
  xslfor-each loop

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xslsort

• You can place an xslsort inside an xslfor-each
• The attribute of the sort tells what field to
  sort on
• Example
  select"//book" select"author"/
  • select"title"/ by select"author"
  
  
• This example creates a list of titles and
  authors, sorted by author

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Book example

• 
  
  
• 
  Table of Contents
  
  
  template
• Etc.

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xslapply-templates

• The element applies a
  template rule to the current element or to the
  current elements child nodes
• If we add a select attribute, it applies the
  template rule only to the child that matches
• If we have multiple
  elements with select attributes, the child nodes
  are processed in the same order as the
  elements

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When templates are ignored

• Templates arent used unless they are applied
• Exception Processing always starts with
  select"/"
• If it didnt, nothing would ever happen
• If your templates are ignored, you probably
  forgot to apply them
• If you apply a template to an element that has
  child elements, templates are not automatically
  applied to those child elements

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Applying templates to children
With this lineXML by Gregory Brill

• XML
  Gregory Brill
• 
  / select"/book/author"/
  match"/book/author" by select"."/

Without this lineXML
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An Example
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