Virtual enterprise is typically one kind of information-based enterprise. The features of information system in virtual enterprise can be generalized as heterogeneous and distributed. Its organization and production management put an essential requirement on information integration. In this paper, we shall discuss the forms of conflict in schema integration of multiple databases in virtual enterprise, and give an approach to resolve the conflicts. In order to implement this approach in relational database, an extended relational data model is proposed and the notion of marked partial value is introduced. Based on this extended data model, some relational operations for data management are defined. A case study is discussed about query processing on relational database with partial values.