This is special circumstances where I have

master site www.xxxxx.com located under public-html

I want to have a slave site www.xxxxx.com/alfa under public-html/alfa so slave site is synchronization of the master site (both master and slave would be same all the time, for example if somebody added article in one it would also appear on the other).

I think the simple question is that can we have one set tables which can be used by both master and slave site?

If you want to have 2 websites with exactly the same content, you can create a JMS template rule where you select that you want to "Share Whole Site".

In this case, this will be the same as create 2 websites using the same DB with same table prefix.