Side is related to Line. Line is a type of Cover. Cover is related to Place. Place is a type of Estimate. 
you are likely to find Ceiling in/at/on Classroom. you are likely to find People in/at/on Classroom. Sofa can be used for People. 
Side <--RelatedTo--> Line --IsA--> Cover <--RelatedTo--> Place --IsA--> Estimate 
Ceiling --AtLocation--> Classroom <--AtLocation-- People <--UsedFor-- Sofa 