Hello Julio,
It doesn't matter what was the technology behind the solution, or it's typical ERP or not, as long as the database is available, uses more common technology and has necessary data,
2 general approaches are possible:
1) Static analysis - download data as csv/excel or convert data to it (it can be done even without direct access to database) .
2) Dynamic/constant analysis - Check what's the database behind every legacy system that should be connected. Create connection between Celonis and database.
After selecting one of those approaches (or mix of them), you can follow standard implementation steps, so:
A) Identify which events in the systems should be visualised
B) Check where data for them is located within the data base (one of the methods is created unique value to check whole database for it. Example: XXXXXXXX_FineMe001_xxxxxxxxx as invoice number)
C) Create activities based on those tables in event collection
D) Finalize the data model, start creating analysis, do agile - waterfall won't usually do well in such use cases.
Such questions can be answered while doing training on Celonis Academy (data Engineer training track), but it requires a lot of time. You can also hire expert to provide you with support.
Best Regards,
Mateusz Dudek