Howto generate index contents

Hi guys,

I have a problem. I generated a pdf-file with docbook. My index content is so:

1. chapter1...............................1
    xxxxx....................................1
    xxxxx....................................2
    ...
2. chapter2...............................5
    xxxxx....................................6
    xxxxx....................................7
    ...
How can I generate an docbook such as below:

1. chapter1...............................1
    1.1 xxxxx..............................1
    1.2 xxxxx..............................2
    ...
2. chapter2...............................5
    2.1 xxxxx..............................6
    2.2 xxxxx..............................7

Can anyone help me?

Thanks