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Hello I got the definition below for an actor. That means the system cannot be an actor to itself. I was wondering what if the system is supposed to display certain elements on a screeen. In that case would the system be its own actor in the system? Probably not . Then how would I present that in a use case diagram ?

Actors: An actor is a person, organization, or external system that plays a role in one or more interactions with your system. Actors are drawn as stick figures. - See more at: http://www.agilemodeling.com/artifacts/useCaseDiagram.htm#sthash.1jE5S2CY.dpuf"

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The system can display certain elements on a screen, means that an actor can "Check those elements on the screen". Try not to describe your system from the point of view of the "system", but from the "Users" point of view: what can they do with the system?

I believe an example would help:

Let's say I want to talk about an ATM as a system. The use cases the "Bank Customer" can use:

  • Withdraw Money
  • Check Account Balance

It would not be ok to describe from the Banks point of view. But If you try you should get something like: The system can:

  • Give money on request (maps to withdraw money)
  • Display balance (maps to Check acct. balance)
  • Great Thanks! :) Also one more question; while drawing a use case diagram, is it neccesary to differentiate between primary and supporting actors ? if so how ? – Cemre Uludag Feb 6 '15 at 12:20
  • I have seen examples in which it is stated on the top of the use case which is the main actor and which is the secondary or supporting actor. I usually don't do this myself, but I do write use cases which points to other use case (for example an use case of another actor). I prefer this way because it helps me to keep only one actor per use case, and this helps me to analyze the profiles later. Anyway, this is more of each person style. – pietromenna Feb 6 '15 at 12:27
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    Besides the bank ATM example, for display systems, two examples you can think about. 1. A system that displays waiting times in a hospital waiting room. Actors: the various patients. Use case: patients want to see if their appointment is delayed and how long they have to wait. 2. Display system for Train schedules (or airline flights). Actors: passengers and people waiting for travellers to arrive. Use case(s): passengers want to see when their train departs (1), which train goes where (2), which transfer they have to make (3), when a train/plane arrives (4), etc.. – Kasper van den Berg Feb 6 '15 at 12:38
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Who are the viewers of the screen? Aren't they the ones who "want" to view the information?

About the question "Can a system be its own actor?"

Perhaps a system can be its own actor. If you view a system as an intelligent goal driven agent that is proactive towards its own goals and acting based on its beliefs, desires, obligations, and intentions (see, amongst others the work of the Intelligent Systems group at the Utrecht University), then one could vie that system as its on actor.

But let me emphasize, I don't think this way of modelling would help you for the display system.

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