To develop a generic ERP(Enterprise Resource Planning) system which can accommodate various types of manufacturing enterprises, object-oriented methods are commonly applied from analysis to implementation. The objective of OO-ERP (Object-Oriented ERP) systems is the reusability of business objects(components). In practice, one of the critical features for the reusable OO-ERP system would be the capability of interfacing with distributed, heterogeneous data repositories. Consequently, it is essential to provide data repository transparency in OO-ERP systems - business objects do not take care of the locations and types of data repositories. In this paper, we propose Data Object Layer(DOL) that supports such transparency. DOL is a horizontal component through which OO-ERP systems can be seamlessly connected with diverse data repositories.