PHP怎样连接Oracle

$oraUser="username";
$oraPass="password";
$oraDB="(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=数据库ip)(PORT=1521)))(CONNECT_DATA=(SID=数据库SID)))";
$Conn = ocilogon($oraUser,$oraPass,$oraDB) or die( "ORACLE server未启动,请与系统管理员联系.");