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(eXtensible Stylesheet Language) A style sheet standard from the W3C that is used to convert an XML document into many formats for publishing and printing. XSL is similar to the Cascading Style Sheets (CSS) in HTML and is compatible with CSS2. An XML document is converted by an "XSLT Processor," also called an "XSLT Transformation Engine," into the new format based on three sets of XSL description languages, as follows:

#1 - XSL-FO - Convert to Page Formats
The XSL Formatting Objects (XSL-FO) language is used to apply page formatting to an XML document and produce an XSL-FO document. The resulting XSL-FO file, or simply "FO file," serves as a paginated master file for conversion to page-oriented formats such as PDF, PostScript, AFP or PCL. The conversion is handled by a third-party program such as XML Engine for Print (XEP) from RenderX (www.renderx.com) or Apache Formatting Objects Processor (http://xmlgraphics.apache.org/fop).

When a user selects a PDF document on a Web page, the file may actually reside in XSL-FO format and be rendered on the fly to PDF for that user in real time. The XSL-FO format was designed to outlive proprietary page description languages and is a good choice for archiving paginated documents.

#2 - XSLT - Convert to XML, HTML and Text
The XSL Transformation Language (XSLT) is used to convert an XML document into an HTML or text document or to another XML document with a different structure. The most common XSLT transformations are from XML to HTML for rendering in a Web browser. Unlike the paginated format of XSL-FO, HTML pages are structured as scrollable windows of infinite vertical length.

If the XSLT to transform XML to HTML is embedded in an XML document, the document can be converted to HTML on the fly for rendering, just as XSL-FO can be turned into PDF on the fly for downloading.

#3 - Xpath - Select and Calculate
The XML Path Language (Xpath) is used in conjunction with XSL-FO and XSLT to select elements within an XML document. Xpath can also be used to count items; for example, how many times a particular tag occurs in the document. See XQuery, XML and CSS.

XSLT Processing
For conversion, the XML document is parsed into a tree structure, and the XSLT Processor creates a new file based on the descriptions in the XSL-FO, XSLT and Xpath components. This illustration shows the ways XSL can be applied to the document and the common outputs.

XSL-FO to Print
RenderX's XML Engine for Print (XEP) converts XSL-FO documents to PDF, PostScript or IBM's AFP page formats. (Image courtesy of RenderX, www.renderx.com)
References in periodicals archive ?
One tricky part of writing a basic XSL file is using the X-Path language to select or examine specific pieces of data in the XML file.
W3C's XSL Working Group and XML Query Working Group, who created these specifications, have addressed thousands of comments from implementers and the interested public to ensure that the specifications meet the needs of diverse communities.
The new version also features enhanced processing of dynamic XSL.
As a result of extensive experience with XSL-FO for printing and display XML Co more than 20 commercial implementations supporting more than 50 languages Co users and vendors alike called upon the XSL Working Group to standardize a number of popular, but proprietary, extensions.
The Stylus Studio XML application debugging and code generation tools provide unparalleled extensibility, offering seamless integration with the world's leading XML, XQuery, XSL and XSLT processors including DataDirect XQuery[TM], Apache Xalan, Apache Xerces, Microsoft .
E[acute accent]The XSL specification is in two parts: a language for transforming XML documents (XSLT), and an XML vocabulary for specifying formatting semantics (XSL-FO).