Of course, the work isn't over after the new version of your application has been installed and the users trained. You have ongoing maintenance, bug fixes, and planning for the next set of enhancements. As with the implementation phase, you need to be concerned in maintenance with version upgrades of whatever APIs you're using. Even now, over two years after the XML Schema recommendations were published, not all parsers catch or properly report all compliance errors. But they're getting better all the time. Be alert for compliance failures in documents and schemas that previously tested okay. You may need to fix your application code that produces XML, or even fix a schema (or lobby to have it fixed). Following the standard practice of repeating your QA test cycle with new versions of parser APIs will go a long way toward minimizing production downtime.