Les,
Maybe I should have made this a bar bet, but I do those when I have a
(secret) opinion firmly formed on the controversy.
Does the system include the system boundary? If so, is the system
within the system? If the system is not within the system, can it be
said to be external to the system? If the system is external to the
system, and communicating with itself, why can't it be an actor?
Probably, most people would say that the system *is* within the system
boundary, so it can't be an actor.
Is it true that I can't treat anything within the system as an actor?
If I can treat an "untouchable" legacy subsystem as an actor, why not
the system?
Using "Time" instead of "System Clock" as an actor is an interesting
idea -- sort of an Ingmar Bergman thing. The "grim reaper" has already
been used for death, but "father time" is very similar -- do you think
it would be suitable as an icon?
In the end, best practices can include some arbitrary standards, and I
can accept that.
-Eric
[EMAIL PROTECTED] wrote:
>
> Eric,
>
> I think the problem could be caused by 'your students' not having a firm
> idea as the scope of the system.
>
> You might try drawing a context diagram where everyone contributes and
> agrees to the exact boundary to your system.
>
> As for system clock, as an actor, the actor is 'Time' and produces an input
> to your system clock.
>
> The printing issue comes about as a result of not having system scope
> defined. I.e. Is the Printer inside or outside your system? You decide. If
> it's outside, the printer can be an actor, if it's inside then the actor
> is/maybe the printed output or the person the output is for, depends very
> much on why you're sending it to the printer.
>
> Hope this helps,
>
> Les.
>
> When drawing their first use case diagrams, my students (including some
> of my best) sometimes identify the system under development as an actor.
>
> I've been telling them not to do this, since my favorite sources don't
> do it, but lately it has been bothering me.
>
> When the system is doing something like scheduling activities for
> regular or delayed execution, I have seen authorities use a "system
> clock" actor. Also, in some environments it is quite right to say that
> the system provides services such as printing. If the system looks like
> an actor, walks like an actor, and quacks like an actor, what is it?
>
> -Eric
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