Graph theory
 

is the study of graphs, which are mathematical structures used to
model pairwise relations between objects.

A graph in this context is made up of vertices
(also called nodes or points) which are connected by edges
(also called links or lines).

A distinction is made between
undirected graphs, where edges link two vertices symmetrically,
and
directed graphs, where edges link two vertices asymmetrically

Pairwise comparison generally is any process of comparing entities in pairs to judge
which of each entity is preferred, or has a greater amount of some quantitative property,
or whether or not the two entities are identical.

The method of pairwise comparison is used in the scientific study of preferences, attitudes,
voting systems, social choice, public choice, requirements engineering and multiagent AI systems.