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ing many corporations to invest time and money in “creating, purchasing, promoting and advertising SNSs” (boyd & Ellison, 2007).

The evolution of SNSs illustrates the trend and organizational shift of online communities. While websites devoted to interest-sharing communities still exist and thrive, SNSs are mainly structured around people, not interests. They are structured as personal (or “egocentric”) networks and the individual is at the center of his/her community (boyd & Ellison, 2007). This more truthfully reflects “unmediated social structures, where the world is composed of networks, not groups” (Wellman, 1988, p. 37 cited in boyd & Ellison, 2007). The sultry of SNS features has instituted a new organizational structure for online communities, hence, an exciting and dynamic research context.

三、社交网络概述——C. Profiles of SNSs
Even as SNSs have employed a number of technical features, their essentials comprise of profiles displaying a publicly expressed list of “Friends” or contacts who are also users of the system. Profiles are “unique pages where one can type oneself into being” (Sunden, 2003, p. 3). In general, profiles show the user's name, age, sex, location, interests, profile picture and an “About Me” section. Some sites enable users in putting multimedia content and altering their profiles' look and feel.

A profile's visibility differs by site and depending on user discretion. SNS users may choose if they want their profiles to be made public or for “Friends only”. Facebook employs a different approach. By default, Facebook users sharing a common “network” can view each other's profile.

After signing up for an SNS, users are made to identify people in the system with whom they have a relationship. These relationships may be called “Friends”, “Contacts”, and “Fans” - depending on the site. While most sites require two-way confirmation for Friendship, some do not. These one-way ties are usually referred to as “Fans” or “Followers” (Donath & boyd, 2004).

According to boyd and Ellison (2007), the public display of connections is a vital aspect of SNSs. The Friends list show links to each Friend's profile, allowing a viewer to see the person's network simply by browsing through his/her Friends list.

Most SNSs also allow users to send messages to their Friends. This feature involves leaving “comments” or “testimonials” on the profile, and private messaging, which functions like a webmail (Donath & boyd, 2004).

Another significant variation of SNSs is their features and user base. SNSs may or may not have photo or video sharing abilities, built-in ordinary and micro- blogging, and instant messaging technology (Donath & boyd, 2004). Most SNSs target people from certain geographical regions or linguistic groups. Some are designed with definite sexual orientation, ethnic, religious, political, or other identity-driven categories in mind (Donath & boyd, 2004).

四、社交网络和政治——D. SNSs and Politics
While checking out each other's activities or preferences online is a form of social networking, getting involved in politics has grown prominent (Kanter, 2008). Hence, when the networks go online, so do political entities. Supporting a political candidate or cause is a crucial way for people to connect and interact with society and their surround