The function that uses MODIF A to evaluate absences in SAP is RAB1. This operation is part of the payroll process and is used to control access to the table Absence Valuation during absence valuation. MODIF A specifies which employee subgroup groupings in which table entries the system must take into account for absence valuation1.

The function WPBP (Import work center and basic pay data) in SAP HR is used to transfer master data on the work center and basic pay for the payroll period to internal table WPBP.The basic pay wage types are stored in the internal table IT. If all the fields of the table WPBP are same during the entire payroll period, this table will contain one record1. The infotypes imported by function WPBP are:
Infotype 0008 (Basic Pay)
Infotype 0007 (Work Schedules)
Infotype 0001 (Organizational Assignment)
References =
https://community.sap.com/t5/enterprise-resource-planning-blogs-by-members/understanding-functions-in-payro