Creating a "Collapsed Pool" object in Aris Express

Hello Sofija,

first a disclaimer: I have no experience with ARIS Express, but some with BPMN. So please forgive me, if there were a special behaviour in ARIS Express, that I am not aware of.

IMHO there is no such thing as a "Collapsed Pool". BPMN does not distinguish between black box and white box pool symbols. When you put nothing inside a Pool symbol it is a black box pool. If you do, it is a white box pool. In particular you would not place Lanes inside the black box pool, when there is nothing to show inside. You might resize your Pool symbol to be somewhat smaller, when you intend to use only one or few message flows to and from the Pool. That is up to your taste and how the layout works out in your situation.

The black box pool symbol is only used to provide the "border" of the external process.

Best regards, M. Zschuckelt