DOCBOOK: Numbered Section Headers

I would like to make an article with automatically numbered section headers.
For example:

1  This Is The First Main Section 
	some text ...
1.1  This Is A Subsection
	some text ...
1.2  This Is Another Subsection
	some text...

2 This is the Second Main Section
	some text...
2.1  ....

How is this done?

Thanks...

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Larry Singer
BMC Software
Telephone: 713-918-1639
e-mail: