When should you split up your class files into different namespaces? My application isn't very complicated and it's only run by myself.
For example:
I have an admin system, a user message system (a simple system to send the webmaster a message), and a photos rating & commenting system. These three systems will all need to have some kind of input form validation, implemented differently. ie. class AdminValidate implements InputValidator, class MessageValidator implements InputValidator and class PhotosValidator implements InputValidator.
Should these three systems be placed in one namespace, or three separate namespaces? If the former, what would be an appropriate namespace name? If the latter, where should the interface be placed?