Oracle Service Name and Instance Name

Do you know from where oracle picked up below two values in single Instacle database?

[oracle@oraworld.co.uk dbs]$ lsnrctl status

LSNRCTL for Linux: Version 10.2.0.4.0 - Production on 22-MAR-2012 11:51:06

Copyright (c) 1991, 2007, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=oraworld.co.uk)(PORT=1522)))
STATUS of the LISTENER
------------------------
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 10.2.0.4.0 - Production
Start Date                21-DEC-2011 09:54:31
Uptime                    92 days 1 hr. 56 min. 34 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /u01/app/oracle/ora10g/network/admin/listener.ora
Listener Log File         /u01/app/oracle/ora10g/network/log/listener.log
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=oraworld.co.uk)(PORT=1522)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC0)))
Services Summary...
Service "PLSExtProc" has 1 instance(s).
  Instance "PLSExtProc", status UNKNOWN, has 1 handler(s) for this service...

Service "oracledb11g" has 1 instance(s).

  Instance "oracle11g", status READY, has 1 handler(s) for this service...

Service ==  db_unique_name

Instance == ORACLE_SID

As you know, database name shouldn't be more than 8 character but here you could see the service name is more than 8 characters.