you are likely to find People in/at/on Shop. you are likely to find People in/at/on Demonstration. Demonstration is related to Sit. 
Add is a synonym of Join. Join is related to Marriage. Marriage is related to Link. 
Shop <--AtLocation-- People --AtLocation--> Demonstration <--RelatedTo--> Sit 
Add <--Synonym--> Join <--RelatedTo--> Marriage <--RelatedTo--> Link 