Extensible Stylesheet Language (XSL) is the language used to specify rules, while Extensible Markup Language (XML) is the language used for the data that forms an input to the rules. The combination of XML and XSL provides a platform-independent way to express both inputs to the rules evaluator and rules themselves.
You can use XML to express complex data types in a structured and standard manner in text format. Using this text format, you can write rules for processing the XML data without having to cater to platform and programming language specifics.
You can use XSL Transformation (XSLT) rules to convert an XML document into another document in XML, PDF, HTML, or other format. A transformation rule must be defined as an XSL template in an XSL stylesheet. The rule must be written in a valid XSL template rule format. XSL possesses an inherent ability to analyze and evaluate XML data, which is becoming the standard for data representation in e-business models.