Connection properties as Interface Constants in PHP

I bought a PHP Design Patterns book, and the author uses constants to hold connection attributes:

interface IConnect {
   const HOST = "localhost";
   const UNAME = "root";
   const PW = "jerrylewis99";
   const DBNAME = "test";
   public function doConnect();
}

I know this works, but is it correct and usable? What are your thoughts and why do you believe so?