Although it is standard to use two configuration files for Validator, it is not technically required. Both configuration files must conform to the same DTD and thus could be combined into one large file that specifies both the validation routines and their use with forms. However, it's advantageous to have the individual files because you can reuse the validation-rules.xml file in multiple applications. Similarly, if your application uses the Struts module feature, then you will likely have a validation.xml file for each module. Embedding the contents of validator-rules.xml in validation.xml would result in a great deal of redundancy in this scenario.