You can also do the invert thing: create tables directly with you RDBMS tool (SQL Server, Oracle, mySql, Postgresql, etc) then discovering them with the Adobe Campaign client software, menu Tools/Advanced/Database Extension Wizard, then select the table(s) in order to generate automatically the XML source schema with your customer namespace.
Then you have to adapt a bit the xml schema generated to add specific things such as dblinks for joins with other tables, etc.
There is also an admin menu tool for doing the same but at field level.
There are advantages (more powerful to master all the underlying RDBMS possibilities such as specific indexing/primary key/sequences/storage properties), but drawback is the availability of direct RDBMS access (or your database administrator) so probably reserved for On Premise hosting configurations.
creating the data model and the tables- As far as i know, It is possible only by creating a schema (xml, which defines the structure of a table) and updating the database for this schema creates a table out of that. PostgreSQL is used to query the table