Hi Eddie.

Does it use it's own internal SQL database or are we able to connect to our own database and which databases are certified to run against the platform?

Both.

Supported 3rd party databases are listed here:

https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls...

Generally, please see "First looks" guides in our doc, particularly for JDBC and ODBC:

https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls...