Wilhelm Hasselbring INFORMATION SYSTEM INTEGRATION

or information systems, it is increasingly difficult to draw a line around an application system and say that you own and control it. For example, as value chains extend beyond enterprises, supplier and customer systems become part of each other's information architectures. Furthermore , in many application areas, data is distributed over a multitude of heterogeneous, often autonomous information systems, and an exchange of data among them is not easy. Figure 1 illustrates such a vertical fragmentation of organizational units. Each unit may be structured within three architectural layers, as described in the following. The business architecture layer defines the organizational structure and the workflows for business rules and processes. It is a conceptual level expressed in terms meaningful to actual users of application systems. The application architecture layer defines the actual implementation of the business concepts in terms of enterprise applications. At this layer, it is the central goal to provide the " glue " between the application domain described in the business architecture and the technical solutions described in the technology architecture. Research in information systems aims at filling the gap between business and technology, which requires interdisciplinary cooperation between the application domain and information technology. The technology architecture layer defines the information and communication infrastructure. At this layer, IT is challenged to achieve the business requirements. It is important to realize that Figure 1 does not adequately reflect the reality. In practice, the business architectures of the individual organizational units cannot be treated in isolation: the business processes of cooperating units are highly interrelated and should be handled as such. Figure 2 illustrates this situation. Certain kinds of interactions among computer systems resemble interactions among people; thus, it is important to consider all levels when integrating those systems. A horizontal integration of the layers is required to support the business processes effectively, as indicated here. Interorganizational processes. At this layer, business engineering [1] seeks to organize a commercial undertaking in a competitive way, whereby business processes cut horizontally through the traditional organization structure. Business process reengineering aims at continuously improving those processes. To support the intraorganizational business processes within organizations effectively, the existing