A social graph is a diagram that illustrates interconnections among people, groups and organizations in a social network. The term refers to both the social network itself and a diagram representing the network.
Individuals and organizations, called actors, are nodes on the graph. Interdependencies, called ties, can be multiple and diverse, including such characteristics or concepts as age, gender, race, genealogy, chain of command, ideas, financial transactions, trade relationships, political affiliations, club memberships, occupation, education and economic status.
Services such as Facebook facilitate the exchange of information, news, photographs, literary works, music, art, software, opinions or even money among users. In this environment, the social graph or for a particular user consists of the set of nodes and ties connected, directly or indirectly, to that actor.
When portrayed as a diagram, a social graph appears as a set of points or dots connected by lines. The points represent the actors and the lines represent the ties. A small-scale social graph can be drawn with a pencil on a sheet of paper. However, because of the complexity of interconnections between individuals, a social graph is typically too massive to fit on a single page and can be rendered only on a computer equipped with specialized application software. Apache Giraph and Facebook Graph Search allow users to search for information in social graphs.
Speaking at the Facebook f8 event in May 2007, CEO Mark Zuckerberg used the term "social graph" to refer to the network of connections and relationships between site users. Zuckerberg said that "it's the reason Facebook works." He went on to say the social graph is "changing the way the world works... As Facebook adds more and more people with more and more connections it continues growing and becomes more useful at a faster rate. We are going to use it spread information through the social graph."
For the social graph to have the sort of impact that Zuckerberg foresees, however, it will have to overcome some current limitations. Writing on his Web site, Brad Fitzpatrick, a prominent programmer and creator of LiveJournal, explains:
Unfortunately, there doesn't exist a single social graph (or even multiple which interoperate) that's comprehensive and decentralized. Rather, there exists hundreds of disperse social graphs, most of dubious quality and many of them walled gardens... the graph needs to exist outside of Facebook. MySpace also has a lot of good data, but not all of it. Likewise LiveJournal, Digg, Twitter, Zooomr, Pownce, Friendster, Plaxo, the list goes on. More important is that any one of these sites shouldn't own it; nobody/everybody should. It should just exist.
Fitzpatrick lists a primary goal of making the social graph a community asset.