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of mobility permeated society, the community was said to be transforming: social networks of geographically dispersed members developed (Wright, 2008). This broadens the people's communication circles while increasing their opportunities for self-expression (Wright, 2008). Minorities, who had difficulty in the twentieth century to express themselves socially, typify this. This societal trend only enhanced the already great need and desire of people for connection.

The emergence of the Internet, not unlike other technologies before it, created a popular venue for discussion of political and social issues (Holt, 2004). Many scholars have explored the role of computer-mediated communication in political communication (Holt, 2004). In recent years, new web technologies, popularly referred to as social media, have opened up possibilities for rich, online human-to-human interaction unprecedented in the history of Internet Communication. Of these new web technologies, SNSs in particular have created unique arenas for online discourse.

二、社交网络的历史和定义——B. Definition and History of Social Networking Sites
SNS are “web-based services that allow individuals to (1) construct a public or semi-public profile within a bounded system, (2) articulate a list of other users with whom they share a connection, and (3) view and traverse their list of connections and those made by others within the system” (boyd & Ellison, 2007).

SNS are a means for self-presentation and for building and maintaining contact with friends and acquaintances (boyd, 2006; Donath & boyd, 2004; Ellison, Steinfield, & Lampe, 2007). The users have profiles, which usually include their picture and information about their age, hobbies, favorite music and books, and so on. Often, these SNSs have weblog, photo- and video sharing features. Users can leave short messages on the profiles of other members that can be viewed by other users.

According to boyd and Ellison (2007), the first identifiable SNS was introduced in 1997. SixDegrees.com let users build profiles, list their Friends and, starting in 1998, browse the Friends lists (boyd & Ellison, 2007). These features had been offered in other forms before SixDegrees. Profiles were present in most popular dating sites and numerous community sites. AIM and ICQ buddy lists provided lists of Friends while Classmates.com permitted people to affiliate with their high school or college (boyd & Ellison, 2007). SixDegrees pioneered in combining these features and advertised itself as an instrument in helping people connect and send messages to others. (boyd & Ellison, 2007).

SixDegrees attracted millions of users but fell short in becoming a sustainable business and in 2000, the service closed (boyd & Ellison, 2007). Its users said there was not much to do after accepting Friend requests.

Various community tools supporting different kinds and mixtures of profiles and publicly expressed Friends sprouted from 1997 to 2001. AsianAvenue, BlackPlanet, and MiGente offered users personal, professional and dating profiles (O. Wasow, personal communication, August 16, 2007 as cited in boyd & Ellison, 2007). Similarly, LiveJournal, which was launched in 1999, showed one-directional connections on user pages. In 2000, the Swedish web community LunarStorm then rebuilt itself as an SNS; it provided Friends lists