XSL Transformations

From Wikipedia, the free encyclopedia

XSL Transformations
File name extension .xsl, .xslt
Internet media type application/xslt+xml[1]
Developed by World Wide Web Consortium
Type of format Stylesheet language
Extended from XML
Diagram of the basic elements and process flow of Extensible Stylesheet Language Transformations.
Diagram of the basic elements and process flow of Extensible Stylesheet Language Transformations.

Extensible Stylesheet Language Transformations (XSLT) is an XML-based language used for the transformation of XML documents into other XML or "human-readable" documents. The original document is not changed; rather, a new document is created based on the content of an existing one.[2] The new document may be serialized (output) by the processor in standard XML syntax or in another format, such as HTML or plain text.[3] XSLT is most often used to convert data between different XML schemas or to convert XML data into HTML or XHTML documents for web pages, creating a dynamic web page, or into an intermediate XML format that can be converted to PDF documents.

As a language, XSLT is influenced by functional languages,[4] and by text-based pattern matching languages like SNOBOL and awk. Its most direct predecessor was DSSSL, a language that performed the same function for SGML that XSLT performs for XML. XSLT can also be considered as a template processor.

XSLT is Turing complete.[5][6][7][8]

Contents

[edit] Origins

XSLT is developed by the World Wide Web Consortium (W3C). The most recent version is XSLT 2.0, which reached W3C recommendation status on 23 January 2007. As of 2008, however, XSLT 1.0 is still more widely used and implemented.

Originally, XSLT was part of the W3C's Extensible Stylesheet Language (XSL) development effort of 1998–1999, a project that also produced XSL Formatting Objects and the XML Path Language, XPath. The editor of the first version was James Clark. XSLT 1.0 was published as a Recommendation by the W3C on 16 November 1999. After an abortive attempt to create a version 1.1 in 2001, the XSL working group joined forces with the XQuery working group to create XPath 2.0, with a richer data model and type system based on XML Schema. XSLT 2.0, developed under the editorship of Michael Kay, was built on this foundation in 2002–2006.

Most of this article is applicable to both XSLT versions; any differences are noted in the text.

[edit] Overview

The XSLT processing model involves:

  • one or more XML source documents;
  • one or more XSLT stylesheet modules;
  • the XSLT template processing engine (the processor); and
  • one or more result documents.

The XSLT processor ordinarily takes two input documents[9]—an XML source document, and an XSLT stylesheet—and produces an output document. The XSLT stylesheet contains the XSLT program text (or ‘source code’ in other languages) and is itself an XML document. It describes a collection of template rules: instructions and other directives that guide the processor in the production of the output document.

[edit] Template rule processing

The XSLT language is declarative—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: Assuming a stylesheet has already been read and prepared, the processor builds a source tree from the input XML document. It then starts by processing the source tree's root node, finding in the stylesheet the best-matching template for that node, and evaluating the template's contents. Instructions in each template generally direct the processor to either create nodes in the result tree, or process more nodes in the source tree in the same way as the root node. Output is derived from the result tree.

[edit] Processor implementations

XSLT processor implementations fall into two main categories: server-side, and client-side.

Although client-side XSLT processing has been available in Microsoft's Internet Explorer since 1999 (or even earlier, but in a form that was incompatible with the W3C specifications), adoption has been slower because of the widespread deployment of older and alternative browsers without XSLT support. For similar reasons, adoption of XSLT 2.0 in such environments is likely to be some years away.

XSLT processors may be delivered as standalone products, or as components of other software including web browsers, application servers, frameworks such as Java and .NET, or even operating systems. For example, Windows XP comes with the MSXML3 library, which includes an XSLT processor. Earlier versions may be upgraded and there are many alternatives, see the external links section.

[edit] Performance

 This section needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (October 2007)

The performance of XSLT processors has steadily improved as the technology has become more mature, although the very first processor, James Clark's xt, was unbeaten for several years[10].

Most of the earlier XSLT processors were interpreters; in more recent products, 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.[11] This separation is reflected in the design of XSLT processing APIs such as JAXP (Java API for XML Processing).

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 the kind of optimization techniques found in functional programming languages and database query languages, notably static rewriting of the expression tree for example to move calculations out of loops, and lazy pipelined evaluation to reduce the use of memory for 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 much more efficient (in both space and time) than general purpose DOM implementations.

[edit] XSLT and XPath

For more details on this topic, see XPath.

XSLT relies upon the W3C's XPath language for identifying subsets of the source document tree, as well as for performing calculations. XPath also provides a range of functions, which XSLT itself further augments. This reliance upon XPath adds a great deal of power and flexibility to XSLT.

XSLT 2.0 relies on XPath 2.0; both specifications were published on the same date. Similarly, XSLT 1.0 works with XPath 1.0.

[edit] XSLT and XQuery compared

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

XSLT capabilities overlap with 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.

[edit] XSLT examples

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>

[edit] Example 1 (transforming XML to XML)

This XSLT stylesheet provides templates to transform the XML document:

<?xml version="1.0" ?>
<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>

[edit] Example 2 (transforming XML to XHTML)

Example XSLT Stylesheet:

<?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="html"/>
 
<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>

XHTML output that this would produce (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>
  Image:xslt ex2.png



How the XHTML appears when rendered in a web browser.


[edit] References

  1. ^ XSL Transformations (XSLT) Version 2.0
  2. ^ XSL Transformations (XSLT)
  3. ^ See e.g., http://www.w3.org/TR/xslt#output, specifying alternate output methods.
  4. ^ Dimitre Novatchev. Higher-Order Functional Programming with XSLT 2.0 and FXSL. ExtremeMarkupLanguages. Retrieved on January 18, 2007.
  5. ^ Kepser, Stephan. (2004).
  6. ^ A Simple Proof for the Turing-Completeness of XSLT and XQuery. International Digital Enterprise Alliance.
  7. ^ Universal Turing Machine in XSLT
  8. ^ index
  9. ^ Typically, documents are XML files, but the specifications avoid excluding other representations, such as in-memory DOM trees or other conforming input streams.
  10. ^ XML.com: XSLT Processor Benchmarks
  11. ^ Saxon: Anatomy of an XSLT processor - An article describing the implementation and optimization details of a popular Java-based XSLT processor.

[edit] See also

[edit] External links

For implementations, see XML template engine.
Documentation
Mailing lists
Books
XSLT code libraries
  • EXSLT is a widespread community initiative to provide extensions to XSLT.
  • FXSL is a library implementing support for Higher-order functions in XSLT. FXSL is written in XSLT itself.
  • The XSLT Standard Library xsltsl, provides the XSLT developer with a set of XSLT templates for commonly used functions. These are implemented purely in XSLT, that is they do not use any extensions. xsltsl is a SourceForge project.
  • Kernow A GUI for Saxon that provides a point and click interface for running transforms.
  • xslt.js – Transform XML with XSLT JavaScript library that transforms XML with XSLT in the browser.
Further examples
v • d • e
XSL
XSLT (elements) • XSL-FO • XPath
v • d • e
Standards of the World Wide Web Consortium
Recommendations
Canonical XML · CDF · CGI · CSS · DOM · HTML · MathML · OWL · PLS · RDF · RDF Schema · SISR · SMIL · SOAP · SRGS · SSML · SVG · SPARQL · Timed Text · VoiceXML · WSDL · XForms · XHTML · XML · XML Base · XML Events · XML Information Set · XML Schema (W3C) · XML Signature · XPath · XPointer · XQuery · XSL Transformations · XSL-FO · XSL · XLink
Notes
Working Drafts
CCXML · CURIE · InkML · XFrames · XFDL · WICD  · XHTML+MathML+SVG · XBL · HTML 5