1. A method, comprising: recording logical relationship information, the logical relationship information describing logical relationships between a first user and other users, the logical relationship information associated with a social networking service; monitoring communications between the first user and the other users, the communications being of at least two different types of communications; determining, at a server using at least one processor, a first user group in which to add the first user based on the logical relationship information, a first factor and a second factor, the first factor corresponding to a first of the different types of communications and the second factor corresponding to a second of the different types of communications, the determining including applying a first time-varying function to the first factor and a second time-varying function to the second factor to represent an effect of passage of time, the first time-varying function being different than the second time-varying function; and adding the first user to the first user group.