Broadcast date: December 21st, 2021

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Welcome to the 21st door of our MBSE Podcast Advent Calendar. Today, we take a look at the death of the actors.

That doesn’t sound very Christmassy, but we need to talk about it. The actors died a long time ago. Curious? Let’s take a look at it in our model.

Our system context diagram clearly shows actors. So who is dead here?

We need to distinguish the concept “actor” from the SysML model element “actor”. The model element is dead, or rather we bury it.

Why? Let’s take a closer look. So the concept of “actor” is great. So, external entities interact with the system and so on with all the methodological variants that exist.

The SysML model element “actor” is problematic. It comes from UML and is there defined in such a way, that an Actor may not have any ports, receptions, operations, attributes, or parts.

But these are features that are needed now and then. For example, our actor “power supply” has a port, or our actor “room” has a part “floor”.

If we just claimed that a SysML actor couldn’t have that, why could we model that?

Because we did not use the SysML actor. As mentioned at the beginning, the actor is dead respectively nonexistent to us. Formally, our actor kinds from the SYSMOD profile are stereotypes specializing the SysML block. The stereotypes define the appropriate actor semantics.

This is not a nasty workaround but is formally mapped correctly. Even the SysML specification uses this kind of actor modeling in its example Hybrid SUV model.

Thus, actors have the same capabilities as blocks and can have ports, internal structures, and so on.

So we have by no means trashed the concept of the actor, but the SysML model element. The Actor is Dead! Long live the Actor!

So much for the 21st door of our MBSE Podcast Advent Calendar. We wish you a great 21st of December.

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