Could you please share some good books, blogs, sites on practical problem decomposition, thanks P.S. Please only practical ones not the scientific/theoretical resources.
I don't think this is quite the answer you want but it's definitely better than nothing; and you might find it useful in any case.
The closet I've come is the work by Roger Sessions; he's got a thing for reducing complexity - and it has a lot to do with decomposition. I suspect his work is more on the theory side - but it's obviously backed up by a lot of practical examples and experience. I haven't looked at his website (or blog) with a view to find info on decomposition but he might have some material that's more like what you're after; he's also really approachable - why not contact him directly and ask him? I'm sure he'd be happy to point you in the right direction.
I attended a session he presented on this subject at Tech-Ed 2009 (in New Zealand), which I blogged about here if you want more of an overview. It was a really excellent presentation.
Not only was he using decomposition but he was also working out an actual figure that you could use to rate the complexity of the solution you come up with. so I guess this will be more about using decomposition rather than "how" to do it.
Anyway, he spoke of:
"Decompose the problem domain into a "universe of elements" (a list of business functions). Note: This list should still be recognisable to the business."
This might not sound like much, but is a good place to start.