Restrict access to Edition- or instance-specific databases I have the following issue with SQL Server.

On my Windows Sever, SQL Server 2008 Express Edition is running. Now I have installed SQL Server 2008 Web Edition on the same server.

My problem is, when I log in using SQL Server Management Studio of the Web Edition instance, I am able to see, and access, all the databases there, including those created in the Express Edition, which is not what I want.

Is it possible to restrict visibility/accessibility of databases to just those related to the Web Edition when I log in using the Web Edition, and similar for the Express Edition?
There is no way to prevent a client software from accessing a SQL Server instance when correct credentials are supplied. 

SQL Server Management Studio is the same product for all editions (actually, starting from SQL Server 2016, it is a separate product which ships separately from the engine).

Your only option to prevent users from accessing one of the instances in your server is granting permissions only to the people entitled to access the data.