Friday, February 6, 2004 02:45 AM
You must first answer the question what is the boundary of the system/application you are describing? Actors are external to this boundary.
If your application (the system) receives messages from the user, position sensors and interacts with other external devices/users (camera), and these are not considered part of the system then these are all actors.
However, components (image analyser) which are part of the system will not be actors.
Although system boundary definition may appear trivial and is often neglected in use case analysis, it is an essential step in order to build an accurate use case model and fully understand what your system does.
Hopes this helps