This diagram shows a complete transformation chain (exemplary). It begins with your data source, from which the data for the document is extracted as an XML file. The generated XML is then converted to XSL-FO using XSLT (based on the transformation rules in an XSLT stylesheet, see the example below). Apache FOP receives the XSL-FO document and converts/formats it to the desired target format. If you create a PDF you might stream it to the user's browser or send it to your client by e-mail, or if you create a PostScript file, you might print it on a printer.