Chapter 1
Introduction
1.1 What is a social network?
As humans, we form relationships with other humans. Although not all relationships
are pairwise (for example, a newborn baby acquires relationships with both parents
and siblings at the same time), it turns out to be useful to model most relationships
as structures between two participants.
The creation of such pairwise relationships is usually intentional — the two
participants decide to create a mutual relationship. When the creation process is
not intentional, it is typically the result of biological, social, or legal forces. The
adjective “social” in the phrase “social networks” reflects the property that pairwise
relationships occur because of underlying properties of humans and human society.
The networks that we build to connect computers, for example, have quite different
structures and properties.
Although each individual connects to another individual as the result of a
choice (or something like it) made locally, the aggregate of all of these choices is
a network, a spider web of connections among many individuals. The overall structure of this network has many intriguing properties that do not obviously follow from
the choices made by the individuals. The collection of local, individual choices create a structure that has global regularities. We say that a social network has emergent
properties. Looking at these emergent properties enables us to understand something about the large-scale drivers that motivated (mostly unconsciously) the choice
of each pair of individuals to create a relationship.
In other words, large-scale, mostly invisible, forces act to cause pairs of individuals to form relationships; the resulting structure can be analyzed to detect emergent properties; and these properties can, in turn, be used to understand the invisible
forces, which might be difficult to see and interpret in any other way. Social networks, therefore, are a kind of lens that we can use to discover properties of society,
of particular groups, and sometimes particular individuals.
1
Introduction
1.1 What is a social network?
As humans, we form relationships with other humans. Although not all relationships
are pairwise (for example, a newborn baby acquires relationships with both parents
and siblings at the same time), it turns out to be useful to model most relationships
as structures between two participants.
The creation of such pairwise relationships is usually intentional — the two
participants decide to create a mutual relationship. When the creation process is
not intentional, it is typically the result of biological, social, or legal forces. The
adjective “social” in the phrase “social networks” reflects the property that pairwise
relationships occur because of underlying properties of humans and human society.
The networks that we build to connect computers, for example, have quite different
structures and properties.
Although each individual connects to another individual as the result of a
choice (or something like it) made locally, the aggregate of all of these choices is
a network, a spider web of connections among many individuals. The overall structure of this network has many intriguing properties that do not obviously follow from
the choices made by the individuals. The collection of local, individual choices create a structure that has global regularities. We say that a social network has emergent
properties. Looking at these emergent properties enables us to understand something about the large-scale drivers that motivated (mostly unconsciously) the choice
of each pair of individuals to create a relationship.
In other words, large-scale, mostly invisible, forces act to cause pairs of individuals to form relationships; the resulting structure can be analyzed to detect emergent properties; and these properties can, in turn, be used to understand the invisible
forces, which might be difficult to see and interpret in any other way. Social networks, therefore, are a kind of lens that we can use to discover properties of society,
of particular groups, and sometimes particular individuals.
1