There is no specific 'System Sequence Diagram'. Generally for small applications one diagram is sufficient to explain the complete behaviour of the application. In that case sequence diagram is also called as system sequence diagram.


For each use case we can have a sequence diagram. More number sequence diagrams gives you the indepth details of the protocols.

You could create a sequence diagram for the whole system but, unless it's a very small system, I hope that you have a lot of paper to hand and the patience to stitch the sheets together. You could always create a highlevel sequence diagram showing only key behaviour and then smaller ones for more complicated areas.

Regards.