The UML 1.3 defines:
Actor
An actor defines a coherent set of roles that users of an entity can play when interacting with the entity. An actor may be considereded to play a seperate role with regard to each use case with which it communicates. [...]
Use Case
The use case construct is used to define the behavior of a system or other semantic entity without revealing the entity�s internal structure. Each use case specifies a sequence of actions [...]
"users of an entity" is - for me - all that, which is not a part of my system. So the system clock is part of the use case.
Actor UseCase Actor
User ------> Cron --------> external System
Actor: User
can define new Cron-Jobs (which command is on which time?)
Actor: external System
external system or command that is contacted or executed by the cron
UseCase: Cron
- administers the cron-jobs
- checks periodically the jobs
- starts execution of the jobs
Maybe this helps.
Mit freundlichen Gr��en
Jan Mat�rne
RZF NRW
Sachgebiet 314-P Software-Entwicklungs-Methoden
Fiscus AFG NW 42 SoftwareEntwicklungsUmgebung
Internet: [EMAIL PROTECTED]
-----Urspr�ngliche Nachricht-----
Von: Frank I. Reiter [SMTP:[EMAIL PROTECTED]]
Gesendet am: Mittwoch, 21. M�rz 2001 21:41
An: [EMAIL PROTECTED]
Betreff: (ROSE) Use cases: When its not clear who gets the value
I'd like to hear some opinions about how to handle something that has me a
bit stumped.
I am writing use cases for a system. For the most part I am finding that
pretty straight forward. In one instance however there is behaviour that I
want to document and I can't see quite how to make it a use case. (On
possible answer is that I shouldn't try!)
The system has a cache of data which originates elsewhere and can change
over time. Periodically the system checks with the source of truth for
updates. The question that really stumps me is "Who is the actor in this
use case?"
The obvious answer is time or the system clock. I don't really want to do
that because the rule of thumb that resonates best with me is that the actor
is a party outside of the system that gets value from the use case. Time
gets no value from this.
So who does?
Well, I could say that the system does. That would make this a use case of
the external system, with my system as the actor, rather than a use case of
my system. That wouldn't really belong in my document.
Various users benefit in that they are working with more up to date data,
but they get that value through other use cases already written. They do
not participate in this use case at all.
How do people handle this?
Frank.
-----
The very act of seeking sets something in motion to meet us;
something in the universe, or in the unconscious responds as if
to an invitation. - Jean Shinoda Bolen
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