pubic void FillDataSet(DbDataSet dataSet, string connStr) {
        // retrieving data from DEPT table
        PgSqlDataTable dept = new PgSqlDataTable("select * from dept", connStr);
        dept.FetchAll = true;
        dept.Active = true;
      
        // retrieving data from EMP table
        PgSqlDataTable emp = new PgSqlDataTable("select * from emp", connStr);
        emp.FetchAll = true;
        emp.Active = true;

        // adding data tables to PgSqlDataSet
        dataSet.Tables.Add(dept);
        dataSet.Tables.Add(emp);

        // linking tables to allow navigation from parent table rows
        // to corresponding child table rows
        DataColumn parentColumn = dataSet.Tables["DEPT"].Columns["DEPTNO"];
        DataColumn childColumn = dataSet.Tables["EMP"].Columns["DEPTNO"];
        DataRelation relation =        new System.Data.DataRelation("DeptsEmps",
                parentColumn, childColumn);
        dataSet.Relations.Add(relation);
}