Best Practices for modeling multiple databases of the same system

[eaweha]

Usually an DBMS System has more than one database.
Also software systems have often more that one database.

For example a company has a system named Sales that contains three databases.
a product database
a customer and configuration database
a workflow database
The databases are in the same server, e.g. MS SQL Server


In such a scenario, what is the best practice in order to apply the <<Datamodel>> structure?

Create for each database a separate model
<<Datamodel>> Products
<<Datamodel>> Customers
<<Datamodel>> Workflow

Create one model and add for each database a <<Database>> package
<<Datamodel>> Sales
   Logical Model
   <<Database>> Products
   <<Database>> Customers
   <<Database>> Workflow
 
 It's obvious, that if there were three different DBMS, for each DBMS I had to create a <<Datamodel>> each database.
 
  Thanks for you hints and suggestions about the better practice