GraphViz is a DSL (Domain Specific Language) for creating diagram visualizations as images, SVG (Scalable Vector Graphics), etc.

For installation information, see Graphviz: dot .

Many years ago, Microsoft (in Excel, etc.) emphasized that what had often been called graphs were now charts.

A graph is a collection of nodes with connections called edges.

In math, a graph is a collection of vertices with connections called arcs.

A graph is a collection of nodes and edges connecting those nodes.

Computer trees and graphs are collections of nodes (vertices) and edges (arcs) connecting those nodes.

The Facebook graph is a data structure of users and who they know, are friends with, etc.

A large graph is the Facebook graph, with hundreds of millions of nodes (people, groups, organizations, etc.) and billions of edges connecting those nodes.

Mathematicians often call nodes vertices and edges arcs.

Computer scientists often like when names (as in variables) have the same number of letters. The words "node" and "edge" each have four letters. And the letter "v" is often used for "variables" so it is already taken as an abbreviation.

An undirected edge (arc) connects two nodes (vertices) without a direction on the edge (arc).

In the Facebook graph, the "friend" relation goes both ways. Both sides need to agree or accept that relation. It is an undirected edge in the Facebook graph.

A directed edge (arc) connects two nodes (vertices) with a direction on the edge (arc).

In the Facebook graph, a "like" is a relation that goes one way. It is a directed edge. What is "liked" does not have to return the "like".

An undirected graph has no direction on each edge.

A directed graph has a direction on each edge.

A DAG (Directed Acyclic Graph) is a directed graph which has no cycles.

A connected graph with no cycles (directed or undirected) can always be represented as a tree structure. In such cases, one node can be designated as the root node. All other nodes with only one edge connection are leaf nodes.

Note that cross-edges in what looks like a tree is what is called a DAG.

A common type of DAG structure would be your family tree. What you think of as a tree going back in time is actually a DAG since, at some point, some of your ancestors would be the same person. This may be easier to visualize from the other end where, at some point, some descendant of an earlier ancestor would marry and have children to another descendant of an earlier ancestor.

Here is the GraphViz diagram. Here is the code that creates the diagram.
graph { node [fontname="Arial"]; #nodes node1 [label="Hello",shape=box]; node2 [label="world",shape=oval]; #edges node1 -- { node2 }; }

Here is the GraphViz diagram. Here is the code that creates the diagram.
digraph { node [fontname="Arial"]; #nodes node1 [label="Hello",shape=box]; node2 [label="world",shape=oval]; #edges node1 -> { node2 }; }

Here is the GraphViz diagram.

The diagram is a digraph where the tree has interior nodes as a symbol. Here is the code that creates the diagram.
digraph "" { node [fontname="Arial",shape=circle]; # nodes b [label="|"] ; a [label="&"] ; x1 [label="X"] ; y1 [label="Y"] ; d [label="&"] ; c [label="!"] ; x2 [label="X"] ; e [label="!"] ; y2 [label="Y"] ; # edges b -> { a d }; a -> { x1 y1 }; d -> { c e }; c -> { x2 }; e -> { y2 }; }

Here is the GraphViz diagram.

The diagram is a graph where the tree has interior nodes as a symbol. Here is the code that creates the diagram.
graph "" { node [fontname="Arial",shape=circle]; # nodes b [label="|"] ; a [label="&"] ; x1 [label="X"] ; y1 [label="Y"] ; d [label="&"] ; c [label="!"] ; x2 [label="X"] ; e [label="!"] ; y2 [label="Y"] ; # edges b -- { a d }; a -- { x1 y1 }; d -- { c e }; c -- { x2 }; e -- { y2 }; }

Here is the GraphViz diagram.

The diagram is a digraph where the tree has interior nodes as a variable. Here is the code that creates the diagram.
digraph "" { node [fontname="Arial",shape=circle]; # nodes b [label="a"] ; a [label="b"] ; x1 [label="X"] ; y1 [label="Y"] ; d [label="c"] ; c [label="d"] ; x2 [label="X"] ; e [label="e"] ; y2 [label="Y"] ; # edges b -> { a d }; a -> { x1 y1 }; d -> { c e }; c -> { x2 }; e -> { y2 }; }

Here is the GraphViz diagram.

The diagram is a graph where the tree has interior nodes as a variable. Here is the code that creates the diagram.
graph "" { node [fontname="Arial",shape=circle]; # nodes b [label="a"] ; a [label="b"] ; x1 [label="X"] ; y1 [label="Y"] ; d [label="c"] ; c [label="d"] ; x2 [label="X"] ; e [label="e"] ; y2 [label="Y"] ; # edges b -- { a d }; a -- { x1 y1 }; d -- { c e }; c -- { x2 }; e -- { y2 }; }