PHP setting Oracle Connection : Oracle: Connection Failed: ORA-12154: TNS:could not resolve service name

Helo Evreyone... I am novice when it comes to PHP.
In need to access an Oracle database from a PHP form ..(queries will come later but I am unable to create a connection in the first place)

I have programmed iin Java JDBC before and the connection string is as below

url=jdbc:oracle:thin:@server:1521:db

And from The Oracle client(Toad) I connect by using the  
username@server.db

I tried this with PHP but failed to connect
*****************************************************************************************************
<?php
$connection = ora_logon("username@server.db","password");

if ($connection == false){
  echo Ora_ErrorCode($connection).": ".Ora_Error($connection)."<BR>";
  exit;
}  

$cursor = Ora_Open ($connection);
if ($cursor == false){
  echo Ora_ErrorCode($connection).": ".Ora_Error($connection)."<BR>";
  exit;
}  

Ora_Commit ($connection);
Ora_Close ($cursor);
Ora_Logoff ($connection);
?>
*****************************************************************************************************

Thanks for your time