Lets say that I have 2 groups consisted of 2 sub-groups. Each sub-group is consisted of 2 actors.
How can I represent in a UML use-case this actor who is member of a specific sub-group which is part of a bigger group?
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Who cares? I don't think UML has a specific notation for such a thing, but then I don't believe it needs to encompass the entire world. (Try writing complete UML notation for a web front end sometime.) UML was not meant to be engineering drawings. Make the groups or sub-groups the actors in your diagrams and move on. – duffymo Jan 23 '11 at 18:09
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Why do you need to identify a specific individual? Remember Actors represent Roles played by individuals, not the individuals themselves. To use a simple programming analogy, Actors are like classes, individuals are like objects.
If instead you want to represent subset relations among Actors (Roles) then you can use the subtype relation, e.g.
So Premium Members are also Members and in turn also Users. But not all Users are Members, and not all Members are Premium Members.
Now whether going to that level is a good idea is an entirely different question. Judicious use can be helpful, but expansive Actor hierarchies rarely are.
hth.
sfinnie
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The fact, that something in UMl can be used as a class (e.g. actors as stated above) is signified by that element being a subclass of a Classifier (therefore also Class is a Classifier). Actors do describe roles, but don't forget, actors in use cases are not ment for describing user groups for authorization. The point is to identify roles played by different people and systems when interacting with system under design. The point of finding and describing them is to collect all their needs and express them in requirements - e.g. use cases. – Gabriel Ščerbák Jan 25 '11 at 00:19
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@Gabriel: agreed. Hence comment to effect that, even though you *can* do it, doesn't mean you *should*. – sfinnie Jan 25 '11 at 08:21
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