Oracle Database Discussions

Hi folks,

I would like to query some data from MS SQL database through Oracle. In other forum I was pointed to Heterogenous Services, but unfortunatelly I'm having a problem with an initial set up.

Documentation I check:
http://docs.oracle.com/cd/E11882_01/server.112/e11050/admin.htm

http://docs.oracle.com/cd/B19306_01/server.102/b14232/admin.htm

Here is my scenario:
On the same server we are running Oracle database (11g release 11.2) and MS SQL (Microsoft SQL Server Express Edition (64-bit)).

Oracle database:
tnsnames.ora

# tnsnames.ora Network Configuration File: C:\Oracle\product\11.2.0\dbhome_dev\network\admin\tnsnames.ora
# Generated by Oracle configuration tools.

DEV =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = SERVER.AGT.local)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = DEV)
    )
  )


HELIOS = 
   (DESCRIPTION=
       (ADDRESS = (PROTOCOL = TCP)(HOST = SERVER.AGT.local)(PORT = 1521))
       (CONNECT_DATA = 
           (SERVICE_NAME = HELIOSDB)
       )
       (HS = OK)
    )

listener.ora

# listener.ora Network Configuration File: C:\Oracle\product\11.2.0\dbhome_dev\network\admin\listener.ora
# Generated by Oracle configuration tools.

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
      (ADDRESS = (PROTOCOL = TCP)(HOST = SERVER.AGT.local)(PORT = 1521))
    )
  )

ADR_BASE_LISTENER = C:\Oracle

SID_LIST_LISTENER=
  (SID_LIST=
      (SID_DESC=
         (SID_NAME=HELIOSDB)
         (ORACLE_HOME=C:\Oracle\product\11.2.0\dbhome_dev)
         (PROGRAM=dg4odbc)
      )
  )

I'm not sure whether a listener part is configured correctly.

Also, what next should be done?
Where is defined a connection to MS SQL database?

Please guide me with this initial configuration if possible.

Kind regards,
Tomas