## Facts

Chapters > Graphs

Facts (edges) determine the content of a directed graph. They indicate a direct relation between two nodes (objects). Assume that we are given the following facts:

Joan is older than Bob, and Bob is older than Melanie

and we are asked to find out whether Joan is older than Melanie. This would be a trivial task if we knew the singers' birthdays. But even if we don't, we can accomplish the task.

We start by building a model (graph) to solve the problem using the commonsense definition of the notion of one person being older than the other, "person A is born earlier than person B". We define that the notation (Joan,Bob) denotes the fact "Joan is older than Bob".