Legacy system
Definition
A legacy system is business-critical software that is technically outdated but still runs core operations. It typically lacks modern interfaces, which makes it the main constraint — and often the main cost driver — in automation projects.
The pragmatic approach is encapsulation: leave the system in place, expose the data it holds through a controlled interface, and build the new workflow around it.
Full replacement is a separate, much larger decision and rarely a prerequisite for the first automation results.
In practice
- Encapsulate rather than replace as a first step
- Database or file interfaces are more stable than UI robots
- Migration is a separate project with its own business case
Related terms
- API integrationAn API integration connects two systems through their programming interfaces so data moves automatically and reliably. It is the stable alternative to manual re-entry, CSV exchange and interface robots, and it is the backbone of every serious automation.
- Robotic process automation (RPA)Robotic process automation uses software robots that operate existing applications through their user interface — clicking, typing, copying between screens. It automates rule-based routine work without changing the underlying systems, and breaks when those interfaces change.
- Custom softwareCustom software is built around a specific company's processes instead of forcing those processes into a standard product. It is chosen when the workflow is a competitive differentiator, when integration depth matters, or when licence and workaround costs exceed the build.