1. make the .ixl executable in the Properties->Permissions (That was the point)
2. double click to execute the installation
3. double click the BridgePoint_Launcher.sh for starting the application.
The xtUML Editor should be installable on most flavors of Linux. It has been run/tested a lot on RedHat and Ubuntu. And it has been installed on many other distributions. You may find that you need to install a set of dependent libraries to get it going.
Good work, Domonkos.