ConnectionInterface vs. SqlConnectionInterface

In many places ConnectionInterface is used as parameter type, but in method body methods of SqlConnectionInterface are used. So my IDE says that the method does not exist in ConnectionInterface.

Example:

![bildschirmfoto 2014-02-10 um 12 50 19](https://f.cloud.github.com/assets/330436/2125016/f03b3cc2-9249-11e3-8c13-255b08053643.png)