A method and system for determining an updated data source from first and second disparate data sources. A first and second data list is received from the first and second data sources, respectively. The data elements in the first data list matching data elements in the second data list are written to a first aggregation data list. The data elements in the first data list not matching data elements in the second data list are written to an additions data list. The data elements in the second data list not matching data elements in the first data list are written to a first deletions data list. All data elements in the first aggregation data list and the additions data list are written into a second aggregation data list. All data elements matching the data elements in the first deletions data list are written into a second deletions data list.