Question about SQL Plus and Net 8 Assistant

Here is my Oracle question (Oracle 8.0.5.0.0)

1. What is the difference between creating type and table? For example if I wnat to store a person's address ( such as street name, postal code.), is it much better to create a address type or a address table?
2. When I open the OEM, it asks for the user name, password, service and connected as. Actually, what does the service name? is it the one in the Net8 Assistant?
3. When I open the Net 8 Assistant after I complete the installation, I find that there are several Service Names (e.g. TCP-LOOPBACK.WORLD, CMEEXAMPLE.WORLD, BEQ-LOCAL.WORLD, ..) and several Listening Location (e.g. Protocol=IPC with Key=oracle.world, Protocol=IPC with Key=ORCL, Protocol=IPC with Key=EXTPROC0, Protocol=NMP with... and Protocol=TCP with ...)in the Listener. Which one is useless so I can remove?
4. I connected to the SQL Plus in NORMAL mode to create a table. But when I connected as SYSDBA next time and issue "desc table_name", why does it say that there is no such table.

Thanks for your help

Edmond

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