Public Class SqlDatabase
    Public Function Execute()
    ' ...
    End Function
End Class

Public Class ServiceMain
    Private _Database As UIDatabase = New UIDatabase
    ' ...
 
    Public Sub DoAnything()
        _Database.Devices.Register("Test")
    End Sub
 
    Protected Class UIDatabase
        Inherits SqlDatabase
 
        Public Structure Devices
            Private DummyMember As String
 
            Public Sub Register(Nm As String)
                Return Execute("INSERT INTO Devices (Name) VALUES (" & Nm & ")")
            End Sub
        End Structure
    End Class
End Class