ERROR: ORA-12514: TNS:listener does not currently know of service

To avoid the following Error: ORA-12514, i always follow the below way to configure tnsnames.ora and listener.ora.
oracledb1-> sqlplus scott@dgtest
SQL*Plus: Release 10.2.0.3.0 - Production on Wed Jul 30 12:04:04 2007
Copyright (c) 1982, 2006, Oracle. All Rights Reserved.
Enter password:
Connected to:Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - ProductionWith the Partitioning, OLAP and Data Mining options
SQL> show userUSER is "SCOTT"
SQL>
************************************************
Listener.ora Configuration
oracledb1-> cat listener.ora
# listener.ora Network Configuration File: /u01/app/oracle/product/10.2.0/db_1/network/admin/listener.ora
# Generated by Oracle configuration tools.
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SID_NAME = PLSExtProc)
(ORACLE_HOME = /u01/app/oracle/product/10.2.0/db_1)
(PROGRAM = extproc)
)
(SID_DESC =
(GLOBAL_DBNAME = dgtest)
(ORACLE_HOME = /u01/app/oracle/product/10.2.0/db_1)
(SID_NAME = dgtest)
)
)
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.2.134)(PORT = 1522))
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC0))
)
)
***********************************************************
tnsnames.ora ->

oracledb1-> cat tnsnames.ora
# tnsnames.ora Network Configuration File: /u01/app/oracle/product/10.2.0/db_1/network/admin/tnsnames.ora
# Generated by Oracle configuration tools.
LISTENER_DATAWARE =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.2.134)(PORT = 1522))
DGTEST_SD =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.2.135)(PORT = 1522))
)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = dgtest)
)
)
DATAWARE =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.2.134)(PORT = 1522))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = dataware)
)
)
DGTEST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.2.134)(PORT = 1522))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = dgtest)
)
)
EXTPROC_CONNECTION_DATA =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC0))
)
(CONNECT_DATA =
(SID = PLSExtProc)
(PRESENTATION = RO)
)
)
LISTENER_DGTEST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.2.134)(PORT = 1522))
*********************************************************
Please let me know any other way to go with...