Social network analysis
A social network consists of any group of people connected through various social familiarities ranging from casual acquaintance to close familial bonds. Social networks are often the basis of cross-cultural studies in sociology and anthropology. There is also "social network analysis", the mapping and measuring of social networks.
Social networks are studied mathematically using graph theory.
The rule of 150 states that the size of a genuine social network is limited to about 150 members.
The number arises from cross-cultural studies in sociology and especially anthropology of the maximum size of a village (in modern parlance most reasonably understood as an ecovillage). It is theorized in evolutionary psychology that the number may be some kind of limit of average human ability to recognize members and track emotional facts about all members of a group. However, it may be due to economics and the need to track "free riders", as larger groups tend to be easier for cheats and liars to prosper in. Either way, it would seem that social capital is maximized by this size.
Joi Ito suggests that the concept of the social network is crucial to what he calls emergent democracy — the vital link between the creative network of at most a dozen people, and the global power networks created by religion, language, tribe and kin affiliations, and ethical traditions associated with them. These he sees as the only path to a so-called Second Superpower.
Internet social networks
Online social networks became a fad in 2003 with the popularity of such websites as Friendster, Tribe.net (a joint of the Friendster with the Craigslist idea) and LinkedIn. Search engine Google launched Orkut on 22 January 2004.
Sites such as LiveJournal, which encourages interconnection of weblogs, approaches this idea. Further evolution of this idea is the Semantic Social Network, which interconnects both people and weblogs, such as StumbleUpon and Funchain.
Social networks can also be organised around business concepts, as for example in the case of Ecademy, Europe's largest Trusted Business Network.