affirm is a set of Java interfaces and XML-based reference implementation designed to make server-side input validation straightforward. While input validation is most relevant to web-based applications, it is useful under many circumstances. The fundamental scenario is that you have a collection of data that needs to be systematically checked to ensure that is meets some predetermined criteria. The act of validating the input results either in a validated datum or some indication of failure and the optional association to some feedback error message.