Ithaka Digraph

Ithaka Digraph provides a framework for directed graphs.

Features

• Simple digraphs (without edge weights)
• Weighted digraphs (with integer edge weights)
• Double-linked digraphs (to access reverse digraph and incoming edges efficiently)
• Map-based digraph implementation
• Basic algorithms (transitive closure, topological search, strongly/weakly connected components...)
• Hierarchical layout (Sugiyama) implementation
• GraphML and Dot language (Graphvis) export functionality

Survey

Here's a brief introduction the core interfaces and classes.

As a side note, the above image has been rendered from a layout computed by Ithaka Digraph.

Digraph Interface

The interface Digraph<V,E> is a generic type, where V denotes the vertex type and E denotes the edge type.

Vertices are added with

boolean add(V vertex); // add a vertex

When putting edges, nodes are lazily added.

E put(V source, V target, E edge); // put edge from source to target

Vertices and edges can be removed with

boolean remove(V vertex); // remove single vertex and adjacent edges
void removeAll(Collection<V> vertices); // remove several  odes at once
E remove(source, target); // remove a single edge

You can test if a graph contains a vertex or edge with

boolean contains(Object vertex);
boolean contains(Object source, Object target);

Getting an edge value is done with

E get(Object source, Object target);

The vertices can be iterated using

Iterable<V> vertices();

To iterate over edges starting at a given source vertex, use

Iterable<E> targets(vertex);

To serve basic graph properties, we have:

int getVertexCount(); // number of vertices in the graph
int getEdgeCount(); // number of edges in the graph
int getOutDegree(Object vertex); // number of outgoing edges
boolean isAcyclic(); // true if and only if graph is cycle-free

In addition, there are some methods producing new graphs:

Digraph<V,E> reverse(); // create graph with reverse edge direction
Digraph<V,E> subgraph(Set<V> vertices); // create subgraph of given vertices

MapDigraph Class

The MapDigraph<V,E> class implements the Digraph<V,E> interface, using nested maps to store vertices and edges (i.e. Map<V,Map<V,E>>).

Digraph<V,E> digraph = new MapDigraph<V,E>();

There are several constructors to allow control of the type of maps used to store vertices and edges.

SimpleDigraph Interface

The SimpleDigraph<V>interface extends Digraph<V,Boolean> (i.e. it doesn't care about edge values) and adds convenience method

boolean add(V source, V target); // add an edge from source to target

WeightedDigraph Interface

The WeightedDigraph<V> interface extends Digraph<V,Integer> (i.e. has integer weights) and adds convenience methods

void add(V source, E target, int weight); // add edge weight (atomatically inserts the edge if necessary)
int digraph.totalWeight(); // sum of all edge weights

DoubledDigraph Interface

The DoubledDigraph<V,E> interface extends Digraph<V,E> and internally maintains the reverse graph, providing additional methods

Iterable<V> sources(Object vertex);
int getInDegree(Object vertex);

DigraphAdapter Classes

The abstract DigraphAdapter<V,E> class implements a Digraph<V,E> by taking an existing Digraph<V,E> at construction time and delegating all methods to it. Class DigraphAdapter is extended by

SimpleDigraphAdapter<V> extends DigraphAdapter<V,Boolean> implements SimpleDigraph<V> { ... }
WeightedDigraphAdapter<V> extends DigraphAdapter<V,Integer> implements WeightedDigraph<V> { ... }
DoubledDigraphAdapter<V,E> extends DigraphAdapter<V,E> implements DoubledDigraph<V,E> { ... }

Digraphs Class

The Digraphs class provides static utility methods ala Collections. To name a few:

<V,E> DoubledDigraph<V,E> emptyDigraph(); // get an unmodifiable empty digraph
<V,E> Digraph<V,E> unmodifiableDigraph(Digraph<V,E> digraph) // wrap graph to make it unmodifiable 
<V> List<V> topsort(Digraph<V,?> digraph, boolean descending); // perform topological sort
<V> Set<V> closure(Digraph<V,?> digraph, V source); // compute transitive closure
<V> boolean isAcyclic(Digraph<V,?> digraph); // test for cycle-freeness
<V> boolean isStronglyConnected(Digraph<V,?> digraph); // test for strong connectivity
<V> boolean isReachable(Digraph<V,?> digraph, V source, V target); // test for existing path
<V> List<Set<V>> scc(Digraph<V,?> digraph); // compute strongly conntected components
<V> List<Set<V>> wcc(Digraph<V,?> digraph); // compute weakly connected components
<V> void dfs(Digraph<V,?> digraph, V source, Set<? super V> discovered, Collection<? super V> finished);
...

Layout Sample

SimpleDigraph<Integer> digraph = new SimpleDigraphAdapter<Integer>();
digraph.add(1, 2);
digraph.add(1, 3);
digraph.add(2, 3);

DigraphLayoutDimensionProvider<Integer> dimensionProvider = new DigraphLayoutDimensionProvider<Integer>() {
	@Override
	public DigraphLayoutDimension getDimension(Integer node) {
		return new DigraphLayoutDimension(String.valueOf(node).length(), 1);
	}
};
DigraphLayoutBuilder<Integer,Boolean> builder = new SugiyamaBuilder<Integer,Boolean>(1, 1);
DigraphLayout<Integer,Boolean> layout = builder.build(digraph, dimensionProvider);
for (DigraphLayoutNode<Integer> vertex : layout.getLayoutGraph().vertices()) {
	System.out.println(node.getVertex() + " --> " + vertex.getPoint());
}

prints

1 --> (1,0)
2 --> (0,2)
3 --> (1,4)

Ithaka Digraph does not contain code to render layouts.

Downloads

Add Maven repository

<repository>
	<id>ithaka</id>
	<url>http://beckchr.github.com/ithaka-maven/mvnrepo/</url>
</repository>

as well as dependency

<dependency>
	<groupId>de.odysseus.ithaka</groupId>
	<artifactId>ithaka-digraph</artifactId>
	<version>1.0</version>
</dependency>

or manually grab latest JARs here.

License

Ithaka Digraph is available under the Apache License, Version 2.0.

(c) 2012 Odysseus Software