@private
Each class including this module has its own client class. Generally it is the service namespace suffixed by client:
@return Retruns the proper client class for the given model.
@return [String] The short name of the service as used in coniguration.
(e.g. SimpleDB::Client.config_prefix #=> 'simple_db')
@return [String] A sensible default inspect string.
[Validate]