Database properties as Interface Constants in PHP

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

interface IConnectInfo {
  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?