Legacy integration aims to revitalize and extend the reach and lifetime of legacy systems by exposing existing functionality through the use of wrapping. It adds a front-end software layer to hide unwanted complexity and exposes modern interfaces to ease interoperability. The options for integrating legacy systems are:
User-interface wrapping or screen scraping, where legacy screens are mapped into modern graphical or Web service interfaces. Advances in the capabilities of Web-based, screen-scraping products make development of these interfaces easier with nominal development effort. However, this option makes sense only for applications that are user-interface intensive.
Data wrapping, where new interfaces are developed for the legacy data structures to allow direct access using standard SQL or XML technologies.
Business-logic wrapping, where legacy functionalities are wrapped and programmatically accessed through custom object-oriented wrappers, EAI adapters, or Web Services interfaces.
Legacy wrapping requires less up-front architecture and design, and it can reduce integration costs and provide a roadmap to incrementally reengineer and transfer legacy components to a new platform without having to go through a "big bang" type of replacement of the system. However, legacy wrapping can only provide a tactical, short-term solution because it addresses the integration and flexibility pain points without impacting the source code significantly. True flexibility will be achieved only by understanding the legacy source code repository and refactoring it to some extent.
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