Social network service uses software to build online social networks for communities of people who share interests and activities or who are interested in exploring the interests and activities of others.
Most services are primarily web-based and provide a collection of various ways for users to interact, such as chat, messaging, email, video, voice chat, file sharing, blogging, discussion groups, and so on. Social networking has revolutionized the way we communicate and share information with one another in today's society. Various social networking websites are being used by millions of people everyday on a regular basis and it now seems that social networking is a part of everyday life. The main types of social networking services are those which contain directories of some categories (such as former classmates), means to connect with friends (usually with self-description pages), and recommender systems linked to trust. Popular methods now combine many of these, with MySpace and Facebook being the most widely used in North America; Bebo, MySpace, Skyrock Blog, Facebook and Hi5 in parts of Europe; Orkut and Hi5 in South America and Central America; and Friendster, Orkut, CyWorld and Mixi in Asia and the Pacific Islands.
There have been some attempts to standardize these services to avoid the need to duplicate entries of friends and interests (see the FOAF standard and the Open Source Initiative), but this has led to some concerns about privacy.
History of social networking services
The notion that individual computers linked electronically could form the basis of computer mediated social interaction and networking was suggested early on . There were many early efforts to support social networks via computer-mediated communication, including Usenet, ARPANET, LISTSERV, bulletin board services (BBS), and EIES: Murray Turoff's server-based Electronic Information Exchange Service (Turoff and Hiltz, 1978, 1993). The Information Routing Group developed a schema about how the proto-Internet might support this.
Early social networking websites included Classmates.com (1995), focusing on ties with former school mates, and SixDegrees.com (1997), focusing on indirect ties. User profiles could be created, messages sent to users held on a friends list and other members could be sought out who had similar interests to yours in their profiles  Whilst these features had existed in some form before SixDegrees.com came about, this would be the first time these functions were available in one package. Despite these new developments (that would later catch on and become immensely popular), the website simply wasn't profitable and eventually shut down . It was even described by the website's owner  as simply ahead of its time. Two different models of social networking that came about in 1999 were trust-based, developed by Epinions.com, and friendship-based, such as those developed by Jonathan Bishop and used on some regional UK sites between 1999 and 2001. Innovations included not only showing who is "friends" with whom, but giving users more control over content and connectivity. By 2005, one social networking service MySpace, was reportedly getting more page views than Google, with Facebook, a competitor, rapidly growing in size. In 2007, Facebook began allowing externally-developed add-on applications, and some applications enabled the graphing of a user's own social network - thus linking social networks and social networking.
Social networking began to flourish as a component of business internet strategy at around March 2005 when Yahoo launched bought MySpace, followed by ITV (UK) buying Friends Reunited in December 2005. Various social networking sites have sprung up catering to different languages and countries. It is estimated that combined there are now over 200 social networking sites using these existing and emerging social networking models, without counting the niche social networks (also referred to as vertical social networks) made possible by services such as Ning and KickApps. .
Research on the social impact of social networking software
An increasing number of academic commentators are becoming interested in studying Facebook and other social networking tools. Social science researchers have begun to investigate what the impact of this might be on society. Typical articles have investigated issues such as
A special issue of the Journal for Computer-Mediated Communications was dedicated to studies of social network sites. Included in this issue is an introduction to social network sites. A list of academic scholarship on these sites is also available.
Social networks connect people at low cost; this can be beneficial for entrepreneurs and small businesses looking to expand their contact base. These networks often act as a customer relationship management tool for companies selling products and services. Companies can also use social networks for advertising in the form of banners and text ads. Since businesses operate globally, social networks can make it easier to keep in touch with contacts around the world.
A good example of social networking being used for business purposes is LinkedIn.com. It is a social networking site with the aim of connecting professionals together. It has, become one of the most powerful and widely used professional networking sites, with more than 20 million registered users from 150 different industries.
Professional networking sites function as online meeting places for business and industry professionals. Other sites are bringing this model for niche business professional networking.
Virtual communities for business allow individuals to be accessible. People establish their real identity in a verifiable place. These individuals then interact with each other or within groups that share common business interests and goals. They can also post their own user generated content in the form of blogs, pictures, slide shows and videos. Like a social network, the consumer essentially becomes the publisher.
A professional network is used for the business to business marketplace. These networks improve the ability for people to advance professionally. Business professionals can share experiences with others who have a need to learn from similar experiences. Additionally, the ability to find, connect and network with other business professionals is one reason why LinkedIn is so popular.
The traditional way to interact is face-to-face. Interactive technology makes it possible for people to network with their peers from anywhere, at anytime in an online environment. Professional network services attract, aggregate and assemble large business-focused audiences by creating informative and interactive meeting places.
Social networks are beginning to be adopted by healthcare professionals as a means to manage institutional knowledge, disseminate peer to peer knowledge and to highlight individual physicians and institutions. The advantage of using a dedicated medical social networking site is that all the members are screened against the state licensing board list of practitioners.
The role of social networks is especially of interest to pharmaceutical companies who spend approximately "32 percent of their marketing dollars" attempting to influence the opinion leaders of social networks.
Social networks for social good
Several websites are beginning to tap into the power of the social networking model for social good. Such models may be highly successful for connecting otherwise fragmented industries and small organizations without the resources to reach a broader audience with interested and passionate users. Users benefit by interacting with a like minded community and finding a channel for their energy and giving.  Examples include SixDegrees.org (Kevin Bacon) and Network for Good. The charity badge is often used within the above context.
Typical structure of a social networking service
In general, social networking services allow users to create a profile for themselves, and can be broken down into two broad categories: internal social networking (ISN) and external social networking (ESN) sites, such as MySpace, Facebook and Bebo. Both types can increase the feeling of community among people. An ISN is a closed/private community that consists of a group of people within a company, association, society, education provider and organization or even an "invite only" group created by a user in an ESN. An ESN is open/public and available to all web users to communicate and are designed to attract advertisers. ESN's can be smaller specialised communities ie linked by a single common interest eg www.TheSocialGolfer.com, www.acountrylife.com, www.greatcookscommunity.com or they can be large generic social networking sites eg MySpace, Facebook etc. However, whether specialised or generic there is commonality across the general approach of social networking sites. Users can upload a picture of themselves, create their 'profile' and can often be "friends" with other users. In most social networking services, both users must confirm that they are friends before they are linked. For example, if Alice lists Bob as a friend, then Bob would have to approve Alice's friend request before they are listed as friends. Some social networking sites have a "favorites" feature that does not need approval from the other user. Social networks usually have privacy controls that allows the user to choose who can view their profile or contact them, etc.
Some social networks have additional features, such as the ability to create groups that share common interests or affiliations, upload videos, and hold discussions in forums. Geosocial networking co-opts internet mapping services to organize user participation around geographic features and their attributes.
There is also a trend for more interoperability between social networks led by technologies such as OpenID and OpenSocial.
Few social networks currently charge money for membership. In part, this may be because social networking is a relatively new service, and the value of using them has not been firmly established in customers' minds. Companies such as MySpace and Facebook sell online advertising on their site. Hence, they are seeking large memberships, and charging for membership would be counter productive. Some believe that the deeper information that the sites have on each user will allow much better targeted advertising than any other site can currently provide. Sites are also seeking other ways to make money, such as by creating an online marketplace (Facebook's Marketplace) or by selling professional information and social connections to businesses: such as LinkedIn.
Social networks operate under an autonomous business model, in which a social network's members serve dual roles as both the suppliers and the consumers of content. This is in contrast to a traditional business model, where the suppliers and consumers are distinct agents. Revenue is typically gained in the autonomous business model via advertisements, but subscription-based revenue is possible when membership and content levels are sufficiently high.
On large social networking services, there have been growing concerns about users giving out too much personal information and the threat of sexual predators. Users of these services need to be aware of data theft or viruses. However, large services, such as MySpace, often work with law enforcement to try to prevent such incidents.
In addition, there is a perceived privacy threat in relation to placing too much personal information in the hands of large corporations or governmental bodies, allowing a profile to be produced on an individual's behavior on which decisions, detrimental to an individual, may be taken.
Furthermore, there is an issue over the control of data - information having been altered or removed by the user may in fact be retained and/or passed to 3rd parties. This danger was highlighted when the controversial social networking site Quechup harvested e-mail addresses from users' e-mail accounts for use in a spamming operation.
In medical and scientific research, asking subjects for information about their behaviors is normally strictly scrutinized by institutional review boards, for example, to ensure that adolescents and their parents have informed consent. It is not clear whether the same rules apply to researchers who collect data from social networking sites. These sites often contain a great deal of data that is hard to obtain via traditional means. Even though the data are public, republishing it in a research paper might be considered invasion of privacy.
Social network services are increasingly being used in legal and criminal investigations. Information posted on sites such as MySpace and Facebook has been used by police, probation, and university officials to prosecute users of said sites. In some situations, content posted on MySpace has been used in court.
Facebook is increasingly being used by school administrations and law enforcement agencies as a source of evidence against student users. The site, the number one online destination for college students, allows users to create profile pages with personal details. These pages can be viewed by other registered users from the same school which often include resident assistants and campus police who have signed-up for the service.