OutSystems integrates with external databases, making it possible to use data from those databases in your OutSystems applications.
For this, you can use the 'Connect to External Table or View' wizard in Integration Studio. It will automatically create a connector to the external database and allow you to use the data from the external database in a transparent way, by defining entities and entity attributes that you can use in Service Studio as part of the application data layer.
For the list of supported external databases please see the System Requirements.
The import process is composed of several steps done in different tools. Follow the Connect to an External Database instructions that will take you through all the required steps.