There is an additional edge come with the Umbrella in order to collect the overflowing,so that the table will remain clean.The reason why the bowl called umbrella is the additional edge is like the Umbrella which can prevent bacteria from growing and also can lift the bottom up to keep the inside clean when you need to stack multiple bowls.
There are a lot of germs on our hands,we can get ill if the edge of the bowl get contaminated by dirty hands.Now,we can hold the Umbrella with the additional edge instead of contacting the edge which our mouth touched