Hi Domeniko,
Connections between IT systems can be created in the System landscape model type.
ARIS Express provides only a reduced set of connections for each model type. In particular, there is only one connection allowed between two objects. ARIS Express shouldn't confuse beginners by offering too many symbols and connections.
The connection between IT systems in the System landscape model type is the 'encompasses' connection which can be used to describe the hierarchical structure of IT systems.
For more experienced users, I would like to recommend the ARIS Business Architect. It provides additional model types and connections to describe relationships between systems, e.g. Access diagram or Application collaboration diagram. The following connections are available in the mentioned model types: 'calls', 'uses', 'transmits data to'.
Kind regards,
Dagmar
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