Conclusion

Legacy systems integration is a huge and complicated topic that merits a whole book of its own. In this chapter we've merely scratched the surface, but we've given you an overview of the more common issues surrounding legacy integration. Some of the issues stemmed from the fact that most legacy systems simply were not designed for the kind of availability and scalability demanded by today's applications. We also briefly discussed the different ways in which applications can interact with a legacy system, and we identified a few methods, including data-level, process-level, and API-level interfacing, and discussed their characteristics and problems. Finally we provided a description of an XML-based, layered architecture that can be used to implement extensible legacy integration solutions.