We'll go into this aspect a little further in the section dedicated to the interaction layer, but it is important to remember that loosely coupled systems are a requirement in the B2B chain. Before interacting with the world, you must first enable integration and communication between all your in-house systems. This is a truly difficult task that requires many different skills. Indeed, integrating SAP using its Business API is very different from integrating SAP with Cobol CICS programs. The first aspect that has to be considered is connectivity between systems.
Connectivity requires that each system to be integrated have dedicated bricks.
However, at the top integration layer, all the connectors plugged into your heterogeneous systems must provide a unified view so as to allow the next step which is building business processes. Performance impact and transition integrity are the two main issues that need to be addressed when creating live back-end interaction. Although transaction integrity can be tricky, it is manageable. The main reason behind this difficulty is that it is very hard to predict what kind of load you will have to handle. Caching technologies such as GemStone's Shared Object Cache could be used to address this problem because they limit access to back-end systems.