The Essence of Software: Why Concepts Matter for Great Design

by Daniel Jackson

In Facebook, for example, you might describe the purpose of the friend concept as “allowing two users to establish a relationship in which they can see each others’ posts.” The problem with this formulation is that it hides two distinct purposes. One is filtering: by promoting posts from your friends, Facebook saves you the trouble of sifting through posts from people you’re not interested in. The other is access control: by choosing your friends, you can choose who gets to see your posts. For most users these purposes are indeed often aligned because human relationships tend to be symmetrical: if I’m happy for you to see posts about my personal life, I’m probably interested in seeing posts about yours too. But for celebrities, the symmetry breaks down. I might want to read Barack Obama’s posts, but I doubt he would want to read mine. Recognizing this, in 2011, Facebook added the concept of follower, which serves only the filtering purpose and not the access control purpose. The friend concept still plays both roles, but you can use it solely for access control by turning off “following” for friends whose posts you don’t want to see.