1. Härder, T., Sauter, G., Thomas, J.: The Intrinsic Problems of Structural Heterogeneity and an Approach to their Solution.VLDB Journal 8:1 (1999) 25–43
2. Sheth, A.P., Larson, J.A.: Federated Database Systems for Managing Distributed, Heterogeneous, and Autonomous Databases. ACM Computing Surveys 22:3 (1990) 183–236
3. Hergula, K., Härder, T.: A Middleware Approach for Combining Heterogeneous Data Sources-Integration of Generic Queries and Predefined Function Access. Proc. 1st Int. Conf. on Web Information Systems Engineering, Hongkong (2000) 22–29
4. Leymann, F., Roller, D.: Production Workflow: Concepts and Techniques, Prentice Hall (2000)
5. ISO & ANSI: Database Languages-SQL-Part 9: Management of External Data, Working Draft (2000)