Back-end systems do not always produce CDF. They should not be expected to produce it, either. Therefore, General Interface runs the XML through an intermediate style sheet that can be supplied by developer. XML Transformer is a property of data-driven General Interface controls that can contain a reference to a style sheet, which will be used to transform XML data before rendering it onscreen using the General Interface style sheet for that control. This allows for very elegant application design where the back end can supply data in a standard XML format, and clients such as General Interface can transform that data to the format they can use. XML Transformer can also be used to manipulate the data before rendering it onscreen; for example, data can be sorted on several keys before passing on to the General Interface handlers. General Interface allows fields to be designated as sort keys. However, XML Transformers can be used to sort the data using a fixed XPath expression before applying the single column sort offered by General Interface.
Note that when you have full control over the back-end XML generation, and/or the sole purpose of generated XML is to feed it to TIBCO General Interface front end, it is best to produce CDF directly because it saves one step in General Interface processing. Transformers are a fast and efficient way to convert XML that is already being generated by some back-end application or when there are other client applications that require the full power of XML.
Chapter 4, "Working with XML and XSL," and Chapter 8 in this book discuss XML Transformers in more detail and provide a complete example of using XML Transformers in General Interface applications.