both 'has' and 'is' are valid prefixes for method that return boolean. the trick is to ask a question in the method name :)
Btw, don't we use too many interfaces? ;)
Imo abstract entities should be used  for most common classes, so IBackend looks good to me but IApacheBackend is not, since it isn't a general case. With the current speed of abstraction we will be stricken by perfomance loss in autoloader very soon.