Why can't I grant execute on a directory?

Question

Why can't I grant execute to a directory?
I have carried out the following:
Login as SYS
Prove that the oracle directory exists SELECT * FROM all_directories WHERE directory_name = 'dir_name';
GRANT EXECUTE ON DIRECTORY dir_name TO role_name;
The following documentation at the following address says that I can grant execute:
http://www.morganslibrary.org/reference/directories.html
And yet when I directed the dba to do it and when I query the database to see if He did it it shows me that he did:
GRANTOR                        GRANTEE                        TABLE_SCHEMA                   TABLE_NAME                     PRIVILEGE                                GRANTABLE HIERARCHY
SYSTEM                         role_name                    SYS                            dir_name                     EXECUTE                                  NO        NO       
SYSTEM                         role_name                    SYS                            dir_name                     READ                                     NO        NO       
SYSTEM                         role_name                    SYS                            dir_name                     WRITE                                    NO        NO       
3 rows selectedWhen I try it in my xe environment it throws the error:
Error starting at line 1 in command:
GRANT EXECUTE ON DIRECTORY dir_name TO role_name
Error report:
SQL Error: ORA-22928: invalid privilege on directories
22928. 00000 -  "invalid privilege on directories"
*Cause:    An attempt was made to grant or revoke an invalid privilege on a
           directory.
*Action:   Only CREATE, DELETE, READ and WRITE privileges can be granted or
           revoked on directories. Do not grant or revoke other privileges.What is going on?
Benton

Answer 1

Benton wrote:
Why can't I grant execute to a directory?Because you can't, according to the 10g documentation...
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_9013.htm#BGEJEBCJ
However in 11g, it can be done...
http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/statements_9013.htm#BGBCIIEG