... When you're thinking about a system, it is often helpful to think about just a part of the system rather than the system as a whole. To do this, you define a limited "scope" around a particular subsystem. In this case, an Actor represents the role something from outside your subsystem plays when interacting with something inside your subsystem.
The "something" can be an object, a person, a separate computer system, a corporation...
Thanks Steve, You cleared up my confusion.
How should I look at roles in ZPatterns?
This is all standard object-oriented stuff, and is not specific to ZPatterns. Get the Coad book, read it, and things should get clearer :-)
It's on my ToReadList :-)
Also, the Catalysis method puts an emphasis on defining interactions and collaborations between objects in terms of roles. You might want to take a look at that.
Is Catalysis method a pattern in Coads book? Regards, Johan Carlsson