XSLT

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XSLT
Paradigm(s)Declarative
DeveloperW3C
Stable release2.0
Preview release3.0
Major implementationslibxslt, Saxon, Xalan
Influenced byDSSSL
WebsiteW3C Transformation
 
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XSLT
Paradigm(s)Declarative
DeveloperW3C
Stable release2.0
Preview release3.0
Major implementationslibxslt, Saxon, Xalan
Influenced byDSSSL
WebsiteW3C Transformation

XSLT (Extensible Stylesheet Language Transformations) is a language for transforming XML documents into other XML documents,[1] or other objects such as HTML for web pages, plain text or into XSL Formatting Objects which can then be converted to PDF, PostScript and PNG.[2]

The original document is not changed; rather, a new document is created based on the content of an existing one.[3] Typically, input documents are XML files, but anything from which the processor can build an XQuery and XPath Data Model can be used, for example relational database tables, or geographical information systems.[1]

XSLT is a Turing-complete language, meaning it can specify any computation that can be performed by a computer.[4]

History[edit]

XSLT is influenced by functional languages,[5] and by text-based pattern matching languages like SNOBOL and awk. Its most direct predecessor is DSSSL, which did for SGML what XSLT does for XML.[6]

Design and processing model[edit]

Diagram of the basic elements and process flow of Extensible Stylesheet Language Transformations.

The XSLT processor takes one or more XML source documents, plus one or more XSLT stylesheets, and processes them to produce an output document. In contrast to widely-implemented imperative programming languages like C, XSLT is declarative.[15] This makes a given XSLT program more resilient to change to the input it is likely to receive, useful in a language used for information processing applications. The basic processing paradigm is pattern matching.[16] Rather than listing an imperative sequence of actions to perform in a stateful environment, template rules only define how to handle a node matching a particular XPath-like pattern, if the processor should happen to encounter one, and the contents of the templates effectively comprise functional expressions that directly represent their evaluated form: the result tree, which is the basis of the processor's output.

The processor follows a fixed algorithm.[17] First, assuming a stylesheet has already been read and prepared, the processor builds a source tree from the input XML document. It then processes the source tree's root node, finds the best-matching template for that node in the stylesheet, and evaluates the template's contents. Instructions in each template generally direct the processor to either create nodes in the result tree, or to process more nodes in the source tree in the same way as the root node. Output derives from the result tree.

Processor implementations[edit]

Performance[edit]

Most early XSLT processors were interpreters. More recently, code generation is increasingly common, using portable intermediate languages (such as Java bytecode or .NET Common Intermediate Language) as the target. However, even the interpretive products generally offer separate analysis and execution phases, allowing an optimized expression tree to be created in memory and reused to perform multiple transformations. This gives substantial performance benefits in online publishing applications, where the same transformation is applied many times per second to different source documents.[41] This separation is reflected in the design of XSLT processing APIs (such as JAXP).

Early XSLT processors had very few optimizations. Stylesheet documents were read into Document Object Models and the processor would act on them directly. XPath engines were also not optimized. Increasingly, however, XSLT processors use optimization techniques found in functional programming languages and database query languages, such as static rewriting of an expression tree (e.g., to move calculations out of loops), and lazy pipelined evaluation to reduce the memory footprint of intermediate results (and allow "early exit" when the processor can evaluate an expression such as following-sibling::*[1] without a complete evaluation of all subexpressions). Many processors also use tree representations that are significantly more efficient (in both space and time) than general-purpose DOM implementations.

In June 2014, Debbie Lockett and Michael Kay introduced an open-source benchmarking framework for XSLT processors called XT-Speedo.[42]

XSLT and XPath[edit]

For more details on this topic, see XPath.

XSLT uses XPath to identify subsets of the source document tree and perform calculations. XPath also provides a range of functions, which XSLT itself further augments.

XSLT 1.0 uses XPath 1.0. XSLT 2.0 uses XPath 2.0. And XSLT 3.0 uses XPath 3.0. In the case of 1.0 and 2.0, the specifications were published on the same date. With 3.0, however, they were no longer synchronized; XPath 3.0 became a Recommendation in April 2014, while XSLT 3.0 was still work in progress.

XSLT and XQuery compared[edit]

For more details on this topic, see XQuery § XQuery and XSLT compared.

XSLT functionalities overlap with those of XQuery, which was initially conceived as a query language for large collections of XML documents.

The XSLT 2.0 and XQuery 1.0 standards were developed by separate working groups within W3C, working together to ensure a common approach where appropriate. They share the same data model, type system, and function library, and both include XPath 2.0 as a sublanguage.

The two languages, however, are rooted in different traditions and serve the needs of different communities. XSLT was primarily conceived as a stylesheet language whose primary goal was to render XML for the human reader on screen, on the web (as web template language), or on paper. XQuery was primarily conceived as a database query language in the tradition of SQL.

Because the two languages originate in different communities, XSLT is stronger in its handling of narrative documents with more flexible structure, while XQuery is stronger in its data handling, for example when performing relational joins.[citation needed]

XSLT media types[edit]

The <output> element can optionally take the attribute media-type, which allows one to set the media type (or MIME type) for the resulting output, for example: <xsl:output output="xml" media-type="application/xml"/>. The XSLT 1.0 recommendation recommends the more general attribute types text/xml and application/xml since for a long time there was no registered media type for XSLT. During this time text/xsl became the de facto standard. In XSLT 1.0 it was not specified how the media-type values should be used.

With the release of the XSLT 2.0, the W3C recommended the registration of the MIME media type application/xslt+xml[43] and it was later registered with the Internet Assigned Numbers Authority[44]

Pre-1.0 working drafts of XSLT used text/xsl in their embedding examples, and this type was implemented and continues to be promoted by Microsoft in Internet Explorer[45] and MSXML. It is also widely recognized in the xml-stylesheet processing instruction by other browsers. In practice, therefore, users wanting to control transformation in the browser using this processing instruction are obliged to use this unregistered media type.[46]

XSLT examples[edit]

Sample of incoming XML document

 <?xml version="1.0" ?> <persons>   <person username="JS1">     <name>John</name>     <family-name>Smith</family-name>   </person>   <person username="MI1">     <name>Morka</name>     <family-name>Ismincius</family-name>   </person> </persons> 

Example 1 (transforming XML to XML)[edit]

This XSLT stylesheet provides templates to transform the XML document:

 <?xml version="1.0" encoding="UTF-8"?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">   <xsl:output method="xml" indent="yes"/>     <xsl:template match="/persons">     <root>       <xsl:apply-templates select="person"/>     </root>   </xsl:template>     <xsl:template match="person">     <name username="{@username}">       <xsl:value-of select="name" />     </name>   </xsl:template>   </xsl:stylesheet> 

Its evaluation results in a new XML document, having another structure:

 <?xml version="1.0" encoding="UTF-8"?> <root>   <name username="JS1">John</name>   <name username="MI1">Morka</name> </root> 

Example 2 (transforming XML to XHTML)[edit]

Processing the following example XSLT file

 <?xml version="1.0" encoding="UTF-8"?> <xsl:stylesheet   version="1.0"   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"   xmlns="http://www.w3.org/1999/xhtml">     <xsl:output method="xml" indent="yes" encoding="UTF-8"/>     <xsl:template match="/persons">     <html>       <head> <title>Testing XML Example</title> </head>       <body>         <h1>Persons</h1>         <ul>           <xsl:apply-templates select="person">             <xsl:sort select="family-name" />           </xsl:apply-templates>         </ul>       </body>     </html>   </xsl:template>     <xsl:template match="person">     <li>       <xsl:value-of select="family-name"/><xsl:text>, </xsl:text><xsl:value-of select="name"/>     </li>   </xsl:template>   </xsl:stylesheet> 

with the XML input file shown above results in the following XHTML (whitespace has been adjusted here for clarity):

 <?xml version="1.0" encoding="UTF-8"?> <html xmlns="http://www.w3.org/1999/xhtml">   <head> <title>Testing XML Example</title> </head>   <body>     <h1>Persons</h1>       <ul>         <li>Ismincius, Morka</li>         <li>Smith, John</li>       </ul>   </body> </html> 

This XHTML generates the output below when rendered in a web browser.

Rendered XHTML generated from an XML input file and an XSLT transformation.

In order for a web browser to be able automatically to apply an XSL transformation to an XML document on display, an XML stylesheet processing instruction can be inserted into XML. So, for example, if the stylesheet in Example 2 above were available as "example2.xsl", the following instruction could be added to the original incoming XML:[47]

 <?xml-stylesheet href="example2.xsl" type="text/xsl" ?> 

In this example, text/xsl is technically incorrect according to the W3C specifications, but it is the only media type that is widely supported across browsers as of 2009.

See also[edit]

References[edit]

  1. ^ a b "Transformation". 2012-09-19. 
  2. ^ "XML Output Method". 2012-09-19. 
  3. ^ "Introduction". XSL Transformations (XSLT) Version 1.0 W3C Recommendation. W3C. 16 November 1999. Retrieved November 7, 2012. 
  4. ^ Kepser, Stephan. "A Simple Proof for the Turing-Completeness of XSLT and XQuery". Proceedings of Extreme Markup Languages. Retrieved 28 October 2012. 
  5. ^ Dimitre Novatchev. "Higher-Order Functional Programming with XSLT 2.0 and FXSL". ExtremeMarkupLanguages. Retrieved August 8, 2009. 
  6. ^ "A Proposal for XSL". W3C. Retrieved November 7, 2012. 
  7. ^ "XML and Semantic Web W3C Standards Timeline". 
  8. ^ "XSL Transformations (XSLT) Version 1.1". W3.org. 2001-08-24. Retrieved 2014-07-12. 
  9. ^ "XML Path Language (XPath) 2.0 (Second Edition)". W3.org. 2010-12-14. Retrieved 2014-07-12. 
  10. ^ "XSL Transformations (XSLT) Version 2.0". W3.org. 2007-01-23. Retrieved 2014-07-12. 
  11. ^ "XML and Semantic Web W3C Standards Timeline". 2012-02-04. 
  12. ^ "XSL Transformations (XSLT)". W3.org. 1999-11-16. Retrieved 2014-07-12. 
  13. ^ "What's New in XSLT 3.0?". w3. Retrieved 6 January 2014. 
  14. ^ Kay, Michael. "A Streaming XSLT Processor". Balisage: The Markup Conference 2010 Proceedings. Retrieved 15 February 2012. 
  15. ^ "Discover the Wonders of XSLT: XSLT Quirks". XSLT is a very specialized language with a distinct declarative flavor. 
  16. ^ Kay, Michael. "What kind of language is XSLT?". IBM. Retrieved 13 November 2013. 
  17. ^ "XSLT Definitions". XSLT declarations define a set of rules and guidelines that are applied during processing according to a predefined algorithm. 
  18. ^ "RaptorXML". Retrieved 21 August 2013. 
  19. ^ "The XSLT C library for GNOME: libxslt". Retrieved 23 November 2012. 
  20. ^ "The XSLT C library for GNOME: The xsltproc tool". Retrieved 23 November 2012. 
  21. ^ "xsltproc man page". Retrieved 23 November 2012. 
  22. ^ "New package: libxslt". Retrieved 23 November 2012. 
  23. ^ "The WebKit Open Source Project - XSLT". Retrieved 2009-10-25. 
  24. ^ "The XML C parser and toolkit of Gnome: Python and bindings". Retrieved 23 November 2012. 
  25. ^ "XML::LibXSLT - Interface to the GNOME libxslt library". CPAN. Retrieved 23 November 2012. 
  26. ^ "libxslt-ruby". Retrieved 23 November 2012. 
  27. ^ "libxml". Retrieved 23 November 2012. 
  28. ^ "cl-libxml2 High-level wrapper around libxml2 and libxslt libraries". 
  29. ^ "TclXML". Retrieved 21 May 2013. 
  30. ^ "libxml++". sourceforge.net. Retrieved 23 November 2012. 
  31. ^ "Command Line Transformation Utility (msxsl.exe)". Microsoft. Retrieved 22 October 2012. 
  32. ^ "Saxon Client Edition 1.0". Saxonica. Retrieved 14 August 2012. 
  33. ^ "QuiXSLT » QuiX-Tool Suite". Project.inria.fr. 2013-11-14. Retrieved 2014-07-12. 
  34. ^ Saxonica. "About Saxon-CE". Retrieved 2012-06-16. 
  35. ^ Frameless. "Frameless XSLT/XPath 2.0 processor". Retrieved 2014-06-09. 
  36. ^ Delpratt, O'Neil (June 2013). "XML on the web: is it still relevant?". XML London 2013: 35–48. doi:10.14337/XMLLondon13.Delpratt01. ISBN 978-0-9926471-0-0. 
  37. ^ Broersma, Robbert; van der Kolk, Yolijn (June 2014). "Frameless for XML - The Reactive Revolution". XML London 2014: 128–132. doi:10.14337/XMLLondon14.Broersma01. ISBN 978-0-9926471-1-7. 
  38. ^ "Can't read an XML and/or XSLT in Google Chrome". Stack Overflow. 2014. Retrieved 12 July 2014. 
  39. ^ "Xuriella XSLT". 
  40. ^ "Plexippus XPath". 
  41. ^ Saxon: Anatomy of an XSLT processor - Article describing implementation & optimization details of a popular XSLT processor.
  42. ^ Kay, Michael; Lockett, Debbie (June 2014). "Benchmarking XSLT Performance". XML London 2014: 10–23. doi:10.14337/XMLLondon14.Kay01. ISBN 978-0-9926471-1-7. 
  43. ^ "XSL Transformations (XSLT) Version 2.0". W3C. Retrieved 19 October 2012. 
  44. ^ "Application Media Types". IANA. Retrieved 19 October 2012. 
  45. ^ "XSLT Requirements for Viewing XML in a Browser". Microsoft. Retrieved 19 October 2012. 
  46. ^ Kay, Michael (2008). XSLT 2.0 and XPath 2.0 Programmer's Reference. Wiley. p. 100. ISBN 978-0-470-19274-0. 
  47. ^ "XSL Transformations (XSLT) Version 1.0: W3C Recommendation – Embedding Stylesheets". W3C. 16 November 1999. Retrieved 2009-01-06. 

Further reading[edit]

External links[edit]

Documentation
XSLT code libraries