Is there any way to link the actual costs in PJI_FP_XBS_ACCUM_F back to the original expenditures?

Is there any way to trace the actual costs in PJI_FP_XBS_ACCUM_F back to the original expenditures?  I'm trying to find a way to get the appropriate RBS Element ID for individual expenditures.  Is there any table that actually stores the individual transactions that get used in the PJI summary table? Or, is there a function that would tell me what the RBS element id should be for a particular expenditure based on the budgeted amounts for that project?   I'm trying to avoid having to re-write the logic used in the summarization process to map actual costs to budgets.