Using DB connect with Oracle to extract data in BW

Hi ,

till now i jhave learnt how to use flat file as source system to load master data.

In SAP help, i have seen that thru DBConnect, we can easily create a source system of database

.When i try to create sourcesystem Database

It opens a window which has

Logical System Name

& Source System.

What will come under this?

I am treating Logical System Name as OracleSID . So i give =sicom (our local sid to database)

& Source System = Oracle

In next screen in DBMS option = ORA

then username

DB password in both textboxes in same line.

& Save.

Message comes as "Data was saved"

But when I try to come to previous windows , message comes as

Source System= SICOM cannot be accessed.

"Where I went wrong " is what I am unable to get.

I am a novice to BW.

Thanks in advance for the fast answer