Patentable things are: Useful ,Novel and Nonobvious.
When you are doing a patent search, it is not enough to see if something as been patented. You have to ensure that the item has NOT been patented. Because it's a process of elimination, it can be time consuming.
- USPTO search: although there is a keyword search feature, there is no controlled vocabulary, therefore you might miss something if, for example, they used 'shield for rain' instead of 'umbrella'.
- If you start with a quick search in the USPTO, a simple way to find related patents is to find the U.S. Classification, and then do a search using that classification to find patents on the same subject.
-CPC classification example: