Editing Software maintenance (section)

==Alternatives to maintenance==
In software engineering, the term [[legacy system]] does not have a fixed meaning, but often refers to older systems which are large, difficult to modify, and also necessary for current business needs. Often legacy systems are written in obsolete [[programming language]]s, lack documentation, have a deteriorating structure after years of changes, and depend on experts to keep it operational.{{sfn|Tripathy |Naik|2014|pp=187-188}} When dealing with these systems, at some point so much technical debt accumulates that maintenance is not practical or economical.{{sfn|Tripathy |Naik|2014|p=89}} Other choices include:
*Freezing—do no more work on the legacy system.{{sfn|Tripathy |Naik|2014|p=188}} This option may be chosen if the vendor wants to continue to extract revenue as long as possible while avoiding maintenance costs.{{sfn|Tripathy |Naik|2014|p=89}}
*[[Outsourcing]] functionality of the legacy system to a different company, especially if it is not considered a core business function.{{sfn|Tripathy |Naik|2014|p=188}}
*Discarding the existing legacy system and redeveloping a new application from scratch to fulfill the same purpose as the legacy system.{{sfn|Tripathy |Naik|2014|p=188}} However, this approach is inefficient due to discarding a working system, and with this approach there is a danger that the new system will not fulfill changing business requirements.{{sfn|Tripathy |Naik|2014|p=188}}
*Wrapping the legacy application in an [[abstraction layer]] to simplify outdated interfaces.{{sfn|Tripathy |Naik|2014|p=188}} The source code is not modified but the new interface allows a tried and tested component to be accessed by newer applications. This approach does not fix any of the issues with maintaining a legacy system.{{sfn|Tripathy |Naik|2014|p=189}} Databases, functions, and entire applications may be wrapped in this way.{{sfn|Tripathy |Naik|2014|p=191}}
*Migrating the legacy system to a new platform, which can reduce the expense of new software development by reusing the  implementation, design, specification, and requirements of the legacy system.{{sfn|Tripathy |Naik|2014|pp=188-189}} Migration can take 5 to 10 years, but results in greater flexibility and long-term savings in software maintenance.{{sfn|Tripathy |Naik|2014|p=195}} As much as 80 percent of the expense is in testing; that is, ensuring that the new system has the same output as the old system.{{sfn|Tripathy |Naik|2014|p=196}} After the new system is finished, there needs to be a transition from the old system to the new system with minimum disruption to business functions.{{sfn|Tripathy |Naik|2014|p=196}}