We know that the primary actor is the one that initiates a use case and a secondary actor is the one that helps completion of the use case through his specific support. The Primary actor is usually placed at the left side to the boundary of the system and the secondary actor is placed to the right of the boundary of the system. But lets consider a library system where we have two actors , librarian and the reader . Lets consider some specific use cases here :
1) A use case where the library can add books to the library system. In this case the librarian is a primary actor.
2) A use case where the reader borrows a book . More specifically , the reader gives the book that he needs to borrow to the librarian and the librarian scan the book using bar code and enters all the needed info in this system ( reader ID , load time ,….etc ) . In this case the librarian is a secondary actor .
So my question is where to put the librarian in the use case diagram? Right or left to the boundary of the system ? Because in some use cases he is a primary actor and secondary actor in others .
Best Answer
Placing primary actors left and secondary actors right is just a convention to facilitate the reading of the diagram by people who know that convention. This is not part of the UML standard, so you can do as you want.
Personally, if it's a primary actor of one of the UC, I'd put is on the left even if it's a secondary actor of another UC in the same diagram. But it would not be wrong to put in on the other side either.