yes, you could in theory. but say that you use xerces for your parsing/transformation... and xerces ceases to exit. the stop upgrading it, etc... the you are stuck. your code only works with xerces and you need a complete re-write to release next version of your application. jaxp defines how xml should be processed from java code. by using jaxp, you are ensuring yourself that you can plug any xml parser into your code and not have to alter much at all. it is one of the better examples of "program to the interface, not to the implementation."