An electronic bill presentment and payment system including an extensible, customizable, data source independent data layer for accessing a business data repository for processing billing information. The business data repositories use one or more data source formats. A business logic module generating business data requests for data from the business data repository in order to carry out processing of billing information. The business data requests are independent of the one or more data source formats of the business data repository. A data layer descriptor repository stores customizable data source descriptions for generating the data layer. The data layer is generated from the customizable descriptors in the data layer descriptor repository. The data layer module receives the data source independent business data requests and based on the request, the data layer implements a data source specific method for fulfilling the request by accessing data in the business data repository. The data layer module further returns a result back to the business logic module in data source independent format. The data layer descriptor repository preferably includes top-level listings of data sources in the system. The data layer descriptor repository further includes customized data source specifications for the each of the data sources listed in the customized set of data sources.