MEF (WinForms) - Parts dependancy

Question

Hello!

I want to make an extendable application which will serve as framework for parts I am going to build in the future.

Here is the idea:

In all of my application some modules are always present:
- user management module 
- database management module

So my framework App would look like this:

System
   +----- Applications
                  +----- App1  (reading some data from external devices)
                  +----- App2  (sending mail module)
                  +----- App3  (Parse some data from Website)
   +---- System modules
                  +----- User management
                  +----- Database management

So. I want to develop a new application (MEF part) which can optionally use any of system parts.
We can say that some parts depend on other parts.

How do I check if needed system module "User management" is available?

How do I call methods from system modules (AddUser, LoginUser, CreateDB,...)?

Any directions, ideas, comments are very appreciated.

Thanks