This may be something that's entirely wrong, but what I would want to do is to use the same BLL and DAL for multiple modules. Is there someone who knows how to implement this or a good tutorial? I was thinking about creating a different assembly and just adding a reference to this assembly in DNN. But I have no idea on how to do this. Further it would be nice if a module is installed that requires an updated version of this assembly it would also be updated. Right now, I have the BLL and DAL in the App_Code folder. And to distribute it I've created a package with all files in (from BLL, DAL and module), but I think this will always overwrite the files installed by previous modules.

A Scheme:

module 1 ->

module 2 ->  BLL -> DAL

module 3 ->

Thx in advance

It's easy to create a separate BLL and DAL component as a separate DLL : indeed this is the way most modules work.  The trick is really in the design and architecture of your module how you package it together and use your namespaces.    If you package all of your module into one extension, then you'll have no problem including a single dll for the BLL and for the DAL.  If you package the same file into different module packages, then you could run into trouble with versioning if you're not careful about binary compatibility and different versions.

Sounds like you are new not only to DNN but also .Net development.  You add a reference to the Web Application Project by Right Clicking the References node in the project treeview and selecting Add Reference.  I think you could benefit from reviewing a few of the tutorials at two difference sites to ramp up.  I have listed the sites below.  Both charge a nominal fee, but it is small and Well Worth it.

LearnVisualStudio.Net This site offers simple to follow tutorials on developing in .Net and using Visual Studio (any edition).

DNNCreative.com This site is specific to DNN and offers articles and video tutorials that range from admin how toos to development tutorials.

There is another site "Engage" that you may want to check out, however I do not know what they charge, but they are the official DNN Training Provider.

I think these resources will get you where you want to go.
 

Best Regards,

Robert J Collins | Co-Founder & President

Netlogic Corporation