This .NET class wraps the AcDbXrefGraphNode ObjectARX class. 

XrefGraph is a derived class for representing an xref. Each XrefGraphNode represents one xref database. 

An XrefGraph is a representation of the relationship between a host drawing, its xref'd drawings, and any nested xref drawings. Each database or xref BlockTableRecord 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.GraphNode
    Autodesk.AutoCAD.DatabaseServices.XrefGraphNode

Public Class XrefGraphNode
Inherits GraphNode

public class XrefGraphNode : GraphNode;