# Specify the service interface

Folder IService contains:

- File IService.signature which defines the signature of the IService interface.
  Note that the file imports the .types file. In general, the names of imported .types files must be different from the signature file name (to avoid potential name clashes in generated code). The doxygen-style tags in the comments will be used for document generation, as explained later.

- File IService.interface with a dummy state machine.
  Note that there are warnings about unused messages from the signature. By means of the activities in this tutorial, the state machine will gradually be completed for these messages. In general, a state machine describes the interface protocol from the viewpoint of server, i.e. which commands and signals can it receive in any state and which notifications it is allowed to send. Messages that are not specified are not allowed.