Databases Reference
In-Depth Information
is living with someone. A
social network
is the collection of some set
of actors and relations.
There are actually a few different types of social networks. For exam‐
ple, the simplest case is that you have a bunch of actors connected by
ties. This is a construct you'd use to display a Facebook graph—any
two people are either friends or aren't, and any two people can theo‐
retically be friends.
In
bipartite graphs
the connections only exist between two formally
separate classes of objects. So you might have people on the one hand
and companies on the other, and you might connect a person to a
company if she is on the board of that company. Or you could have
people and the things they're possibly interested in, and connect them
if they really are.
Finally, there are
ego networks
, which is typically formed as “the part
of the network surrounding a single person.” For example, it could be
“the subnetwork of my friends on Facebook,” who may also know one
another in certain cases. Studies have shown that people with higher
socioeconomic status have more complicated ego networks, and you
can infer someone's level of social status by looking at their ego
network.
Centrality Measures
The first question people often ask when given a social network is:
who's important here?
Of course, there are different ways to be important, and the different
definitions that attempt to capture something like importance lead to
various
centrality measures
. We introduce here some of the commonly
used examples.
First, there's the notion of
degree
. This counts how many people are
connected to you. So in Facebook parlance, this is the number of
friends you have.
Next, we have the concept of
closeness
: in words, if you are “close” to
everyone, you should have a high closeness score.
To be more precise, we need the notion of distance between nodes in
a
connected graph
, which in the case of a friend network means
everyone is connected with everyone else through some chain of mu‐
tual friends. The distance between nodes
x
and
y
, denoted by
d x
,
y
,
