Integration issues in information system reengineering

We address the problem of how to apply schema integration techniques in legacy system migration, since some issues in the legacy concept: legacy system migration and reengineering are closely related to schema integration methods. The importance of introducing integration issues to legacy system migration is two-fold. (1) To adapt legacy systems to a modern environment requires the integration (harmonization) of requirements for both legacy and modern systems. (2) Because a legacy information system is very large, it has to be decomposed into a number of smaller, relatively independent units in order to make migration easier to the target system. These decomposed units should be reintegrated again after the migration process. This situation becomes more complex and difficult when the legacy system was designed and modified using several requirements and data modelling methods. We pose the initial integration problems regarding these aspects: requirement and function schema integration, and database schema integration.