Hi Michel,
Extending to what Rohit said, if you create a data server with DataSource connector and if the XMIIDATASOURCE is its data source then,that the friend tool comes in picture and MII would not be able to access external tables..
However, I had faced a similar situation where I had to create tables in database and had to use them in MII. Since my DB was MAXDB, I had created tables using their MAXDB studio, then created a SQL Data server in MII using IDBC Connector.
The IDBC configuration I had used is on the image above. Make sure you upload the proper DB driver in MII's JDBC Driver's screen.
The JDBC Driver fields and Server URL may vary from DB to DB you could find it from the vendor website.
Regards
Tufale Ashai.