Question : Visual studio two applikations with the same source file, possible

I'm working on a local application and a webapplication. Both use the same database access layer.
I have also a third webapplication using parts of it.
By now doing changements in one of these application I have to change also the sourcecode in the other sourcecode files. After a while it becomes a mess.

Is there a possibility that different applications are working with the same sourcecode file.
I tried in some way, but the file will be always doubled.

Answer : Visual studio two applikations with the same source file, possible

Yes, you can. Take a look at this:
http://www.experts-exchange.com/Programming/Languages/.NET/Visual_Studio_.NET_2005/Q_25040969.html