Legacy System

Annals of Software Engineering 9 (2000) 293–313

293

Encapsulation of legacy software: A technique for reusing legacy software components
Harry M. Sneed
Prellerweg 5, D-82054 Arget, Bavaria, Germany E-mail: [e-mail]

The following paper reviews the possibilities of encapsulating existing legacy software for reuse in new distributed architectures. It suggests wrapping as an alternative strategy to reengineering and redevelopment. It then defines the levels of granularity at which software can be encapsulated before going on to describe how to construct a wrapper and how to adapt host programs for wrapping. Some wrapping products are discussed and the state of the art summarized. The advantage of wrapping over conventional reengineering is the low cost and even lower risks involved. This is the driving force in the search for improved wrapping technology.

1.

Motivation for encapsulation

Legacy software components can be jobs, transactions, programs, modules or procedures within existing application systems which are more than five years old. Usually these systems are running on a mainframe and are based on an outdated technology such as hierarchical or networked database systems and transaction-oriented teleprocessing monitors with fixed panels. Although the technology with which they have been implemented is out of fashion, the application systems themselves are performing critical business functions in an acceptable and reliable manner. It took a lot of time and effort to develop these systems and specially to test them. Therefore, it is irrational to discard them completely, just because they do not meet current technical requirements. Typical candidates for encapsulation as business objects are batch jobs, online transactions and user subroutines as depicted below. On the other hand, there is a definite need to reengineer existing systems in order to satisfy the needs of modern business practices. It is not possible to restructure

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