This .NET class wraps the AcDbGraph ObjectARX class. 

This class provides a generic graph container implementation. One other class is also involved in the graph mechanism: GraphNode. 

Detection for circular references is done by internally creating a duplicate set of references in each node and then trimming away all leaf nodes, which terminate without circularity. If any nodes remain in the duplicate graph, those nodes exist in a cycle. Graph.FindCycles() is used to set up the internal cycle information and enable several query methods to return information about any cycles found.

Autodesk.AutoCAD.DatabaseServices.Graph
    Autodesk.AutoCAD.DatabaseServices.ObjectIdGraph
    Autodesk.AutoCAD.DatabaseServices.XrefGraph

Public Class Graph
Inherits DisposableWrapper

public class Graph : DisposableWrapper;

GraphNode, XrefGraph, XrefGraphNode