SqlConnectionUsing an User Instance on a local SQL Server Express instance
The User Instance functionality creates a new SQL Server instance on the fly during connect. This works only on a local SQL Server instance and only when connecting using windows authentication over local named pipes. The purpose is to be able to create a full rights SQL Server instance to a user with limited administrative rights on the computer.
Data Source=.\SQLExpress;Integrated Security=true;
This connection string (Using an User Instance on a local SQL Server Express instance using SqlConnection) can be used for connections to SQL Server 2005, SQL Server 2008, SQL Server 2014 and SQL Server 2016.