<?xml version="1.0" encoding="utf-8" ?>
<productxml>
<product>
  <brand>
    <a>123</a>
    <a>456</a>
  </brand>
  <price>
    <a>111</a>
  </price>
</product>
</productxml>

static void Main(string[] args)
        {
            DataSet ds = new DataSet();
            FileStream stream = new FileStream(@"D:\My Projects\WindowsFormsApplication10\ConsoleApplication1\XMLFile2.xml", FileMode.Open);
            ds.ReadXml(stream);
          
            DataRelationCollection col = ds.Tables["price"].ChildRelations;
            foreach (DataRelation r in col)
            {
                Console.WriteLine(r.RelationName);
            }

            Console.Read();
        }