Whenever I try to connect to the PUBS.MDF database, a login failed error message will appear.

I defined the connection string in the web.config file like this:

Code:
<connectionStrings>
    <add name="Pubs" connectionString="Data Source = localhost\SQLEXPRESS; Initial Catalog=Pubs;Integrated Security=SSPI"/>
  </connectionStrings>
And setup the connection in the click event of a button
Code:
Dim connectionString As String = WebConfigurationManager.ConnectionStrings("Pubs").ConnectionString
        
Dim myConnection As New SqlConnection(connectionString)

myConnection.Open()

..........
And I put the PUBS.MDF file in the same folder as the vb source files.

How do I connect to the database correctly?