Hi Roger,
The PRM files actually state the functions that are normally available in a database, including the standard format.
They are what drives the list of functions available when you build the SELECT definition or CONDITION definitions in Information designer... The fact that a function needs aggregation or/not is also determined in there.
For more info please refer the guide.
https://help.sap.com/businessobject/product_guides/boexir3/en/xi3_data_access_guide_en.pdf
Regards,
Siva