How to build sequence diagram with 3 actors?

Question

Overview: This is my activity diagram for the stock management subsystem. I have 3 actors which are the admin, manager, and employee.

Question: Can someone explain to me how can I do my sequence diagram with 3 actors? In my sequence diagram, I need to have interface and controller (primary) not just the entity classes.

Note: I already made the sequence diagram for each of the actors but I don't know how to combine its kinda complicated lol.

Answer 1

Sorry for being provocative, but this is a misunderstanding: actors are by definition external to the system.

In your activity diagram, you modelled activities of the sytem and grouped those activities in partitions (swimlanes. These partitions maybe somehow related to actors, but they are not themselves actors. It's just a (visual) grouping.

Likewise a sequence diagram is meant to represent an interaction within the system. In principle you should not show actors in a sequence diagram. Is is however a common practice and tolerated (although ambiguous) practice to do so:

• You could extend this notation and have a lifeline for each actor, but this would remain very ambiguous and would make a very complex interaction diagram. Even more if considering the combinatorial explosion os possible scenarios with so many actors. You have nothing to gain to do so.
• If you really want actors in a SD, a better approach would be to separate concerns: make one SD diagram per actor, that shows the interactions from the view point of the actor. I understand that you already did this. the activity diagram shows how this fits together. (There is no need to have a giant SD diagrams showing all possible interactions)

Typically, the activity diagram with region is a convenient way to document a workflow with several actors. If you want to really focus on actors in a compelx workflow, a better alternative would proabably be to use BPMN, which is designed for business process modeling.