IT: Legacy System (Definitions)

"A production system that was designed for technology assumptions that are no longer valid or expected to become invalid in the foreseeable future." (Atul Apte, "Java Connector Architecture: Building Custom Connectors and Adapters", 2002)

"Systems that have been inherited from languages, platforms, and techniques earlier than current technology." (Timothy J  Kloppenborg et al, "Project Leadership", 2003)

"A system in operational use that must be sustained. Sustainment is challenging for such systems due to obsolete technology, poor structure, outdated and incomplete documentation, and lack of people with the necessary knowledge and skills." (Richard D Stutzke, "Estimating Software-Intensive Systems: Projects, Products, and Processes", 2005)

"An existing data creation, management, and reporting system in a company generally still in use." (Sharon Allen & Evan Terry, "Beginning Relational Data Modeling" 2nd Ed., 2005)

"A database or application using an out-of-date database engine or application tools. Some legacy systems can be as much as 30, or even 40 years old." (Gavin Powell, "Beginning Database Design", 2006)

"A mature system that serves ongoing needs. Legacy systems are often old, monolithic systems, built using older design approaches and older technologies." (Bruce MacIsaac & Per Kroll, "Agility and Discipline Made Easy: Practices from OpenUP and RUP", 2006)

"An information system that has been developed and modified over a period of time and has become outdated and difficult and costly to maintain but that holds important information and involves processes that are deeply ingrained in an organization. Legacy systems usually are eventually replaced by a new hardware and software configuration." (J P Getty Trust, "Introduction to Metadata" 2nd Ed., 2008)

"Old computer applications on disparate platforms, supported by outdated database systems that are still in use in many companies, as legacies from the past." (Paulraj Ponniah, "Data Warehousing Fundamentals for IT Professionals", 2010)

"Term used to describe the original financial system when implementing a new financial system." (Janice M Roehl-Anderson, "IT Best Practices for Financial Managers", 2010)

"An application implemented outside of, or from a prior version of, an organization’s application architecture. Usually an older application that may be slated for eventual replacement. Legacy systems are often frustrating because they are difficult to change, few people know exactly what they do and how they do it, and/or the technology on which they are dependent is becoming obsolete and unsupportable." (DAMA International, "The DAMA Dictionary of Data Management", 2011)

"Application that has been used for a long period of time and that has been inherited from languages, platforms, and techniques used in earlier technologies." (Linda Volonino & Efraim Turban, "Information Technology for Management" 8th Ed., 2011)

"The older systems used to run the business of the corporation as it was defined 10 or 20 years ago" (Daniel Linstedt & W H Inmon, "Data Architecture: A Primer for the Data Scientist", 2014)

"A legacy system is a business solution that has a few common characteristics with current solutions in the market, such as being based on outdated technology or design, being incompatible or difficult and costly to integrate with current systems, and a potential inability of being purchased from vendors because it is unavailable and discontinued." (Microsoft Learning, "Migrate data and go live with Finance and Operations apps", 2020)

"An old system, technology or computer system that is not supported any more." (Analytics Insight)