effect of site-level phases on cultural transition boundaries

[norbu]

Hello everyone, I am new to OxCal, and apologise for a basic question.

I am currently modelling a cultural transition and would appreciate clarification on how OxCal estimates transition boundaries in hierarchical models.

My main question is: how does the incorporation of site-level phase boundaries influence the estimated transition boundaries between two cultural occupations? Specifically, are the transition boundaries between Culture 1 and Culture 2 derived solely from the combined distribution of all dates within each cultural phase, or are they indirectly computed by the start and end boundaries of individual sites nested within those phases? If so, how does this hierarchical structure affect the posterior estimates of the overall cultural transition interval? 

I would like to understand how this differs from a simpler model in which all radiocarbon dates are placed directly within cultural phases without explicit site-level structuring. 

Thank you so much! 

Here is a sample code: 

Sequence()
{
  Boundary("Culture 1 start");
  Phase("Culture 1")
  {
    Sequence()
    {
      Boundary("Site 1 start");
      Phase("Site 1")
      {
        R_Date(...);
      };
      Boundary("Site 1 end");
    };
    Sequence()
    {
      Boundary("Site 2 start");
      Phase("Site 2")
      {
        R_Date(...);
      };
      Boundary("Site 2 end");
    };
  };
  Boundary("Culture 1 end");
  Boundary("Culture 2 start");

  Phase("Culture 2")
  {
    Sequence()
    {
      Boundary("Site 3 start");
      Phase("Site 3")
      {
        R_Date(...);
      };
      Boundary("Site 3 end");
    };
  };
  Boundary("Culture 2 end");
};