What is a legacy system?

Legacy system: definition and charac­teris­tics

The word “legacy” means inheritance. It refers to software that a company has built up over the years and that still carries orders, invoices or production today, even though the technology, vendor support or developers’ knowledge are long outdated. Age alone does not make a system a legacy system; what matters is that it can hardly be developed further.

Typical characteristics are outdated programming languages or databases, missing documentation, no more security updates, hardly any automated tests, missing interfaces and dependence on individual people. Grown Excel solutions with many macros often fall into this category as well. They are especially common among mid-sized companies because they began as a quick fix and were never replaced.

Risks and options

The risk lies not in the age but in what follows from it: security gaps without updates, rising maintenance costs, the danger of failure when hardware or the operating system changes, and dependence on a few people who hold the knowledge. On top of that, new requirements such as a customer portal or e-invoicing can hardly be implemented.

There are several paths: keep the system and secure it, encapsulate it behind an interface, rework the code step by step, move to a new platform, or replace it completely. Another proven approach is to move functions into a new solution one at a time until the old system becomes redundant.

• Keep and secure: little effort, but the risk remains
• Encapsulate: put an interface (API) in front of the old system
• Refactoring: tidy up and update the code step by step
• Replatforming: move unchanged to a more modern platform
• Replace: new development with data migration

Real-world example: a supplier’s production control

A supplier has controlled its production orders for over twenty years with a self-written database application. The developer has retired, the software only runs on an old PC, and the connection to the new web store fails because there is no interface. If the computer fails, production stops.

Instead of replacing everything at once, an interface is first placed in front of the old application and the data is backed up. Then functions such as order creation and status display are moved one after another into a new web application. Operations continue in the meantime, and the risk stays manageable.

What companies should pay attention to

Start with an inventory: which functions are actually used, which data matters, who knows the system and what dependencies exist? Only then can you decide whether replacement, modernization or encapsulation is economical. Typical mistakes are waiting so long that a failure forces the decision, or rebuilding everything one to one instead of rethinking processes.

Nano Concepts analyzes legacy systems, documents functions and data model and plans the modernization in stages—including data migration and parallel operation, so that day-to-day business is not interrupted. Beforehand you receive a clear recommendation with an effort estimate, so you can compare the cost, benefit and risk of each option.