# 4 Relations

## A conceptual graph is a bipartite graph

It will be remembered that a conceptual graph is a bipartite graph with two different kinds of nodes:

1. Concept nodes
2. Relation nodes

We have already discussed concept nodes. Now we discuss the other kind, relation nodes.

## What are relations?

If concepts can be likened to bricks in a wall, then relations can be likened to the mortar that bonds the bricks together. Relations relate concepts to each other in all of the different ways that concepts can be related.

For example, in the following graph,

```   [Cat]->(On)->[Mat]
"A cat is on a mat"
```

the concepts "Cat" and "Mat" are related by the relation node "On". The concepts "Cat" and "Mat" are the "bricks" of the graph, while "On" is the "mortar" that binds the concepts together.

## Next

With this informal introduction in mind, we now gives some definitions that are useful when thinking and talking about relations.

Prev: 3.5 Quiz: Concepts
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Next: 4.1 Definitions for relations