isRequired()

    boolean isRequired(string objectClassName, string attributename)
This function returns TRUE if the attribute is listed as a required attribute based on the information in your slapd.oc.conf file. Otherwise, it will return FALSE. Note that this function will return false if the attrbibute is listed as allowed.

Example: 

$ldap = new LDAP();
$oc = "organizationalUnit";
$attribute = "businessCategory";
if ($ldap->isRequired($oc, $attribute))
	echo "$attribute is required by the objectClass $oc<br>\n";
else
	echo "$attribute is not required by the objectClass $oc<br>\n";