This .NET class wraps the AcDbXrefGraph ObjectARX class. 

XrefGraph is a derived class for representing xrefs, using the XrefGraphNode class to represent one xref database at each node. 

An XrefGraph is a representation of the relationship between a host drawing, its xref'ed drawings, and any nested xref drawings. Each database or xref block table record is represented by an XrefGraphNode in the graph. The host drawing is always the rootNode. Each reference (between databases) is represented by an edge in the graph, and can be queried by calling GraphNode.in(idx) for what is referencing this node, and GraphNode.out(idx) for what this node references. 

While there can be more than one BlockReference referencing an xref BlockTableRecord, only one corresponding edge is created between each XrefNode.

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

Public Class XrefGraph
Inherits Graph

public class XrefGraph : Graph;