What if our system has no interface at all?

Then there are usually several options left. Many older programs can output reports or lists as files, on which an automatic import can be built. Some allow read access to the database. In other cases we move the automation to a neighbouring point in the workflow where the data arises anyway.

If no route holds, we say so plainly instead of building a fragile construction. A step-by-step change of system is then the more honest answer — plannable via legacy replacement.