From the pattern: "solves the problem of grouping and presenting
XML data in an HTML page. Any opaque application running on any platform can to
provide XML input. An XSL stylesheet then takes this and generates HTML. This process
resembles what SQL's Group By does on database tables."
This pattern is described in an article XML Patterns by Maria Laura Ponisio and Gustavo Rossi
This is a one of a group of the four related patterns described in the article about processing XML on a Web server.