//when source 1 is changed, the associated objects and entities are added to their respective ddls
    protected void SourceDropDown_SelectedIndexChanged(object sender, EventArgs e)
    {
        // clears the drop down lists when the user changes the source
        // (OS)
        ObjectDropDown.Items.Clear();
        CounterDropDown.Items.Clear();
        ServerDropDown.Items.Clear();
        ResultsListBox.Items.Clear();

        // (TB)
        CorrelatorService service = new CorrelatorService();

        List<OCMObject> objects = service.getObjects(int.Parse(SourceDropDown.SelectedValue));
        // add items to 1st object list, dependent on source
        foreach (OCMObject obj in objects)
            ObjectDropDown.Items.Add(new ListItem(obj.name, obj.name));

           List<OCMEntity> entities = service.getEntities(int.Parse(SourceDropDown.SelectedValue));
        // add items to 1st entity list, dependent on source
           foreach (OCMEntity entity in entities)
        ServerDropDown.Items.Add(new ListItem(entity.name, entity.id.ToString()));
    }
    // When source 2 is changed, the associated objects are shown in the 2nd object ddl
    // (OS)
    protected void SourceDropDown2_SelectedIndexChanged(object sender, EventArgs e)
    {
        ObjectDropDown2.Items.Clear();
        CounterDropDown2.Items.Clear();
        ServerDropDown2.Items.Clear();
        ResultsListBox2.Items.Clear();

        CorrelatorService service = new CorrelatorService();

        List<OCMObject> objects = service.getObjects(int.Parse(SourceDropDown2.SelectedValue)); //using value from SourceDropDown2
        //add items to second Objects list
        foreach (OCMObject obj in objects)
        ObjectDropDown2.Items.Add(new ListItem(obj.name, obj.name));

        List<OCMEntity> entities = service.getEntities(int.Parse(SourceDropDown2.SelectedValue));
        //add items to 1st entity list, dependent on source
        foreach (OCMEntity entity in entities)
            ServerDropDown2.Items.Add(new ListItem(entity.name, entity.id.ToString()));
    }