public class MyDS: DataSet
{
   Tables.Add("TestTable");
   Tables["TestTable"].Columns.Add("Id",typeof(int));
   Tables["TestTable"].Columns.Add("Name",typeof(string));
   Tables["TestTable"].PrimaryKey=new DataColumn[]{Tables["TestTable"].Columns["Id"]};

   Tables.Add("TestTableDetail");
   Tables["TestTableDetail"].Columns.Add("Id",typeof(int));
   Tables["TestTableDetail"].Columns.Add("SubId",typeof(int));
   Tables["TestTableDetail"].PrimaryKey=new DataColumn[]{Tables["TestTableDetail"].Columns["Id"],Tables["TestTableDetail"].Columns["SubId"]};

   ForeignKeyConstraint
     fk=new ForeignKeyConstraint("fk_Master_Detail",Tables["TestTable"].Columns["Id"],Tables["TestTableDetail"].Columns["Id"]);

   fk.DeleteRule=Rule.Cascade;
   fk.UpdateRule=Rule.Cascade;
   Tables["TestTableDetail"].Constraints.Add(fk);
   Tables["TestTableDetail"].Columns.Add("Name",typeof(short),"Parent(fk_Master_Detail).Name");
}

...
DataRelation
  rel=new new DataRelation("fk_Master_Detail",Tables["TestTable"].Columns["Id"],Tables["TestTableDetail"].Columns["Id"]);

Relations.Add(rel);
Tables["TestTableDetail"].Columns.Add("Name",typeof(short),"Parent(fk_Master_Detail).Name");

(Tables["TestTableDetail"].Constraints.["fk_Master_Detail"] as System.Data.ForeignKeyConstraint).DeleteRule=Rule.Cascade;