# tnsnames.ora の記述例
ORCL =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = db-server)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = orcl)
    )
  )

PDB1 =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = db-server)(PORT = 1521))
    (CONNECT_DATA = (SERVICE_NAME = pdb1))
  )

もう少し詳しく