Whatever it is you are building (web site, house, software), the fundamental tenet of top-down design is:
Plan it...
Describe it...
Then build it...
This is based on the premise that if you do your best to describe and understand something prior to actually building it, then you will have a better chance of building the right thing once you start.
"Top-Down" refers to the direction of your work... start at the top and work your way down.
The "Top" refers to the highest level of planning you can do for your project.
If you start a business, you may develop a top-down business plan.
For your business, the highest level of planning may be to define the kind of corporate culture you want your company to foster.
Below that, you may define your company's market and how your company will make money (and survive).
"Down" refers to working your way down from the most abstract concepts to the nitty-gritty development of whatever project you are describing.
Continuing our entrepreneur example...
The lowest levels of planning may describe how your companies products or services will technically work. At the low levels, as much detail is given as possible.
Top-Down design demands that you plan your project (before doing it) and...
Quote of the Day (QOD)
"Write it down!"
- Every character on NYPD Blue
Hey, that doesn't sound like much fun.
But wait...