How to design database for personalized voting

I wonder how to create something like is doing twitter, but in relational databases.

One application of FlockDB that Weil cites is deter开发者_运维百科mining which users to show @ replies to. For example, if Ashton Kutcher sends a tweet to @foursquare, it shouldn't show up for all of Kutcher's 6,156,915 followers. It should show up only for users that follow both Kutcher and Foursquare.

It has nothing to do with database design, but with how you query the database.

You definitely store each @follow at separate table, there you will have fields who tweets and who is replied. Than you will show the user X all @follows, in which both tweeting and replied is in set of people who he follows :)