i see there is a join table between a process definition and it's variable definitions.
was that intentional ?
i removed the join table and just embedded a foreign key in the variable_definition table.
let me know if you see drawbacks of this change
the table attribute is not used because we use a one-to-many relationship.
the join table is created only when it is many-to-many.
So I think this attribute can be removed without changing the pvm behavior (and the db schema).